UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF LAND MANAGEMENT OREGON STATE OFFICE Minor revision in road standards, tests for surfacing rock, and other areas such as road terminology have been implemented in Bureau road programs since publication of this handbook. These changes are minor and do not effect the utilization of the handbook as A Guidebook for Logging Planning and Forest Road Engineering. BLM Library Denver Federal Center Bldg. 50, OC-521 P.O. Box 25047 Denver, CO 80225 1961 PREFACE This Handbook was prepared by J. Kenneth Pearce, Professor of Logging Engineering, University of Washington, while employed by the Oregon State Office of the Bureau of Land Management. It has been compiled to fill a need that is not, in its entirety, covered by any existing forestry or civil engineering literature. The technical problems confronting the forest engineer are numer- ous and each problem requires careful judgment in the application of sound logging and road engineering principles correlated with the objectives of multiple use forest management. This Handbook is for forest engineers and foresters engaged in the preparation of logging plans and all phases of road engineer- ing from reconnaissance through construction engineering. It is designed to be used as a reference handbook as well as a text for training and operation purposes. UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF LAND MANAGEMENT Oregon State Office FOREST ENGINEERING HANDBOOK A Guide For Logging Planning Forest Road Engineering DIVISIONS Page 100 Considerations in Logging Planning 4 200 Preparation of the Logging Plan 32 300 Gonsiderations in Road Engineering 50 400 Route Projection and Reconnaissance 78 500 Road Location Surveys 112 600 Soil Engineering 149 700 Road Design 183 800 Construction Engineering and Inspection 209 CONTENTS Page 100 CONSIDERATIONS IN LOGGING PLANNING .1 Introduction ^ 110 PHYSICAL REQUIREMENTS OF YARDING METHODS 111 High-Lead .1 Conditions to which adapted, .2 Yarding distance, .3 Yarding distance table. 112 Skylines .1 Conditions to which adapted, .2 Skyline systems, .3 Swinging distance, .4 Deflection. 113 .2 Crawler tractor roads, 114 .2 Wheel tractor roads. Crawler Tractor .1 Conditions to which adapted, .3 Yarding distance. Wheel Tractor .1 Conditions to which adapted. 115 Pre- logging and Salvage Logging .1 Methods used. 116 Logging Methods for Thinnings .1 Horse skidding, ,2 Tractor skidding. 117 Landings .1 Landing requirements, .2 High- lead landings, .3 Tractor landings, .4 Road gradient at landing. 120 ECONOMIC CONSIDERATION 5 7 8 9 9 9 10 121 Logging Costs 11 .1 Planning determines costs, .2 Cost classifications, .3 High-lead yarding cost factors, .4 High-lead yarding cost formula, .5 Tractor skidding cost factors, .6 Com- bined yardin*g methods, .7 Decking and swinging cost factors, .8 Loading cost factors, .9 Landing cost factors, .10 Road and trucking cost factors, .11 Evaluating an existing road. 1 122 Road Patterns 17 o .1 Road patterns, .2 Systematic con- tour road pattern, ,3 Ridge and valley road pattern, .4 Random road pattern. 123 Optimum Road Spacing 19 .1 Road spacing for high-lead yarding, .2 Road spacing for tractor skidding. 130 PROTECTION CONSIDERATIONS 131 Fire Protection 20 .1 Setting boundaries for fire control, .2 Fire buffer belts, .3 Size of clear-cut. 132 Protection from Wind Damage 20 .1 Physiographic factors in windthrow, .2 Edaphlc and biological factors in windthrow, .3 Selection of wlndfirm setting boundaries, .4 Progressive strip cutting. 133 Watershed and Stream Protection 23 .1 Factors in watershed damage, .2 Watershed protection-cable logging, .3 Watershed protection- tractor logging, .4 Stream protection. 134 Protecting Recreational Values 25 .1 Scenic strips 140 SILVICULTURAL CONSIDERATIONS 141 Clear Cutting 25 .1 Provision for regeneration, .2 Staggered settings, .3 Progressive strip cutting, .4 Contin- uous clear cutting. 142 Partial Cutting 26 .1 Partial cutting in pine. .2 Partial cutting in Douglas-flr. 143 Priority Sequence of Cutting 27 .1 Priority in clear cutting, ,2 Pri- ority in partial cutting. 2 150 OTHER CONSIDERATIONS 28 .1 Safety considerations, .2 Consideration of future cuts. BIBLIOGRAPHY 29 FIGURE 111-1 High-lead Profile 6 FIGURE 111-2 Yarding Roads 6 FIGURE 111-3 Setting Nomenclature 6 FIGURE 122-1 Road Patterns 18 FIGURE 123-1 Chart for Finding Optimum Road Spacing 21 FIGURE 132-1- •2-3 Windthrow 22 3 100 CONSIDERATIONS IN LOGGING PLANNING 100. I INTRODUCTION. Logging planning means determining how the timber on a given tract shall be removed. The logging plan is the "blue- print" for the logging operation. The plan embraces the logging methods, the location of landings and setting boundaries, the sequence of cutting and the entire forest road system for the tract. From felling site to log truck dump, logging is transportation. Moving the logs to the landing historically is termed minor transportation. Loading on trucks and haul- ing over the road system is major transportation. Even access roads, al- though constructed independently of timber sales, are a part of the logging plan. The primary purpose of the access road is to serve the logging. Administrative, protective and recreational uses, although im- portant, are secondary to log hauling. The logging planner is the "architect" of the logging plan. To arrive at the best plan, he must consider many factors. Given the basic data on timber and topography, logging planning requires the concurrent consideration of the following factors; 1, The physical requirements of the applicable logging methods, 2, The most economical combination of yarding costs, road construction costs and trucking costs, 3, The silvicultural system and the priority sequence of cutting. 4, Protection of the uncut stand and soil and water re- sources. 5, The safety of the men working on the landings and tra- veling the roads. Some of these factors may conflict. The final logging plan may be a compromise reached after weighing all factors. The relative weight to be given each factor is an administrative decision based on policy. The logging planning divisions of the Forest Engineering Hand- book are prepared to serve two purposes. The first is to fill some of the gaps in the education of the junior forester. The forest management cur- riculum of most forestry schools is deficient in instruction in logging planning. The second purpose is to serve as a reminder to the more ex- perienced planner of considerations which, in his pre-occupation with the more pressing ones, may be overlooked. 4 110 PHYSICAL REQUIREMENTS OF YARDING METHODS 111 HIGH LEAD 111.1 CONDITIONS TO i^HICH ADAPTED. The high-lead system is best adapted to yarding clear-cut settings. However, with the exercise of care by the yarding crew, the high- lead can also be used for pre-logging the smaller understory trees to save breakage, or for yarding tree selection or partial cuttings. The high-lead operates most efficiently yarding up the slope. When the mainline lead block is above the elevation of the turn of logs, a vertical component of force exerted on the mainline is available to lift the turn over obstacles (see Fig, 111-1), The yarding trails fanning out from the landing disperses the runoff and reduces erosion (see Fig. 111-2). Slash is also scattered. When high-lead yarding down the slope, there is no lift on the turn, above the elevation of the block, to free it from "hang-ups". Yard- ing trails converge at the landing with consequent concentration of runoff and slash. There is a hazard to the men on the landing from sliding logs or chicks. However, on very steep slopes where the bulk of the timber volume felled will come to rest on the lower part of the slope, yarding down-slope is indicated. Where a full circle around a spar tree is yarded, as is common practice on side slopes, it is preferable to have the longer yarding distance on the lower side and the shorter distance on the upper side. 111,2 YARDING DISTANCE, Economic high-lead yarding distance is determined by the following physical factors: 1. The height of the spar tree. The taller the spar, the greater the effective lift on the turn. Spar trees are usually "topped" at the point where the diameter is about 24 inches. Douglas-fir is the only species suit- able for a spar tree. 2. The size of the yarder. Yarder horse power, line speed and drum capacity, 3* The topography. An unobstructed line of sight between any point on the setting and the mainline block is essential for efficient operation. The high-lead cannot yard turns effectively from behind ridges or out of draws where the mainline bends in a vertical plane, 4. The volume per acre to be logged. Light stands generally call for a longer yarding distance than heavy stands in order to keep the combined "fixed per acre" costs of moving, rigging and road changing and the "yarding vari- ble" costs at a minimum 5 FIG. Ill-I HIGH LEAD PROFILE FIG. 111-2 YARDING ROADS FIG. IM-3 SETTING NOMENCLATURE O 6 o 111.3 YARDING DISTANCE TABLE. The following high-lead yarding distance table, representing the concensus of a number of efficient log- ging operators, is given as a general guide for average stands in the Douglas-fir region (see Fig. 111-3): Spar Heights Yarder H. P. Range Spacing Between Landings feet External Yarding Distance feet Long Corner Distance feet Tree 175 250-300 1200 800 1000 Tree 150 200-250 1100 750 950 Tree 125 175-200 1000 700 850 Tree or Steel Tower 100 130-175 1000* 600 800 Steel Tower 90 130-200 900** 600 750 Steel Tower 50 40-80 800 500 650 Mobile Logger SJ8 42 157 300 500 Mobile Logger SJ4 30 170 200 400 * Since less time and the landing spacing cost are is often required shorter. to move and rig up a steel tower **One operator spaces landings at 500 feet intervals 1 and yards only two quarters to each landing. In logging planning for sales of Bureau of Land Management timber where the successful bidder and his equipment is not yet known, the planning has to be based on the size of yarders most commonly used in the locality. The height of spar trees available can be determined from measurement of the dominant trees in the stand. 112 SKYLINES 112.1 CONDITIONS TO WHICH ADAPTED. Skyline systems are adapted to swinging from cold decks or hot decks where swing distances are too long for a high lead swing, where the swing is downhill, or the swing road is over rough or broken terrain. The skyline systems give more lift to the turn to free it from ground conditions and permit faster hauling speeds with consequently greater output. Skyline yarding systems are used to a limited extent in rough terrain where most of the yarding must be done down slope. The use of skyline systems on erosible soils instead of tractors is increasing in the pine region. 112.2 SKYLINE SYSTEMS. The skyline system most commonly used for swinging is the North Bend tight-skyline. For swinging down steep slopes the modified North Bend with a two-part mainline between fall block and carriage gives more lift and better control of the turn. In the pon- derosa pine region on erosible soils where tractor skidding is not per- mitted, the Swiss Wyssen system, the Berger interlocking skidder, and the Skagit slackline are being tested. The Skagit "radio-controlled sky carriage" is being tested in the Douglas-fir region. This is a gravity system as is the Wyssen. For diagrams of cable rigging systems. (1/) 7 o 112.3 SWINGING DISTANCE. Swinging distance is usually twice high-lead yarding distance or 1200 to 1600 feet. Distance is limited by deflection obtainable and the length of skyline available. Skyline yard- ing distance ranges from 1000 to 1500 feet for slackline and skldder, to 5000 feet for the radio controlled sky carriage and the Wyssen system. The Grabinski high-lead, sometimes called the ’’scab skyline", is a modification of the high-lead which enables a lift to be given to the turn to free it from hangups. The butt rigging is attached to a traveling block which is hung on the haulback line. The haulback runs directly from spar tree back to tail block and forward to the butt rigging. This system is useful yarding down steep slopes or across short draws. 112.4 DEFLECTION. The most Important factor in planning a sky- line location is to obtain adequate deflection or sag at the center of the span so the desired turn can be carried with an adequate factor of safety. See section 231 for methods of measuring deflection and computing tension in skylines. 113 CRAWLER TRACTOR 113.1 CONDITIONS TO WHICH ADAPTED. The crawler tractor with logging arch is adapted to logging selection or partial cut settings. In the Douglas-flr region the tractor-arch is adapted to yarding clear cut settings downhill on slopes under 35 to 40 per cent, on soils which do not present an erosion hazard. Since tractor yarding is usually cheaper than high-lead yarding, logging operators prefer to use tractors where topogra- phy permits. A combination sometimes used on sidehill settings is to high- lead the lower side uphill and tractor yard the upper side downhill to the same landing. This increases loader output and reduces the combined yard- ing and loading cost. In the ponderosa pine region, where the tractor is usually the only skidding equipment available, slopes up to 60 per cent or more are tractor logged. However, tractor logging on steep slopes is not a safe practice. 113.2 CRAWLER TRACTOR ROADS. In the Douglas-fir region tractor roads are bulldozed preferably prior to felling the timber. The maximum favorable gradient on tractor roads should be limited to 25 to 30 per cent. The optimum gradient which will result in the fastest round trip time is 15 to 18 per cent. Uphill hauls slow down production and adverse grades on tractor roads are usually limited to 5 or 6 per cent. Recommended prac- tice in locating a tractor road is to follow smooth curves. For safety avoid sharp bends or kinks which cause the rear end of turn of logs to swing wide. Tractor road spacing usually averages 150 to 175 feet. 113.3 YARDING DISTANCE. In the Douglas-fir region the usual external tractor yarding distance is 1200 to 1300 feet with long corners of 1500 to 1700 feet. In the pine region where volumes per acre logged are less, skidding distances are longer. However, the skidding distance should be determined by the optimum road spacing formula based on skidding cost, road construction cost and volume per acre (see Ch. 240). Recom- mended tractor logging references are Q/)and(2/). 8 114 WHEEL TRACTOR 114.1 CONDITIONS TO WHICH ADAPTED. The larger rubber-tired wheel tractor, with logging arch built in or attached, is basically a "roading" or swinging machine. Logs are bunched for the wheel tractor by crawler tractor or hot decked by high-lead. The high gear speed of the wheel tractor is two to three times that of a crawler tractor. Wheel trac- tors are especially well adapted to hauls too long for crawler tractors and too short to be economical for motor trucks because loading and un- loading time would be disproportionate to the hauling time. The possibi- lity of increasing truck road spacing and reducing the amount of road con- struction indicates increased use of wheel tractors in the future, parti- cularly in the pine region. As a sxv’ing system in the Douglas-flr region, the wheel tractor is not limited by distance or deflection as is the sky- line. However, the wheel tractor is best adapted to hauling logs down favorable grades. 114.2 WHEEL TRACTOR ROADS. To realize the advantages of the fast travel time of which wheel tractors are capable, wheel tractor roads should be engineered as carefully as spur truck roads. Studies of wheel tractor operations indicate the optimum gradient range to be between 20 and 30 per cent for favorable grades with a maximum of 40 per cent. Ad- verse grades should be avoided if possible. If unavoidable, adverse grades should be limited to short pitches and a maximum of 15 per cent. For steering control at maximum speed, curves should be limited to a minimum radius of 50 feet or 115 degrees. Experienced operators state that they prefer roads as straight as possible with more consideration given to alignment than to gradient, 115 PRE-LOGGING AND SALVAGE LOGGING 115.1 METHODS USED, Where topographic and soil conditions permit, crawler tractors are used for pre-logging to remove the smaller understory trees to save breakage when the large overstory trees are felled and yarded and to salvage wind thrown or dead trees from leave settings or seed blocks. Where condtt’ons necessitate moving cable methods, mobile steel spars or mobile combination yarding and loading machines are commonly used. Maximum external yarding distance for these machines is about 500 feet. Where the road spacing for the main logging does not permit coverage of the entire area by the pre-logging or sal- vage machines, intermediate temporary summer earth roads can be built midway between the regular turck roads. If short-log trucks are used, trees can be dodged to avoid felling and stump blasting and intermediate temporary roads built quite inexpensively. (4/ ) 116 LOGGING METHODS FOR THINNINGS 116.1 HORSE SKIDDING. Horses are well adapted to skidding small logs such as thinnings in second-growth Douglas-flr, They can work on narrow skid trails and with little damage to the residual stand. Capi- tal Investment in horse and equipment is low. Advantages of horse skiddings are low capital investment, narrow skid trails, and minimum damage to the residual stand. Disadvantages are care and feeding when not working and the difficulty of finding good teamsters. 9 Horses are best suited for skidding down the slope on gradients under 40 percent. Maxirauin skidding distance should not exceed 500 to 600 feet. Skidding up the slope should be avoided. If unavoidable, adverse skidding should be limited to 10 percent gradient and 300 feet skidding distance. (_5 / ) 116.2 TRACTOR SKIDDING. The same requirements given in sec- tions 113 and 114 apply to the small crawler tractors and rubber-tired wheel tractors used in yarding thinnings. External yarding distances are usually 600 to 900 feet. However, skidding distance should be deter- mined by optimum road spacing formula. Tractors are better adapted to adverse hauls since they do not tire as horses do. Man-hour production is greater with the tractor. Tractor roads should be kept as straight as possible to avoid damage to residual trees by scraping them with the tractor or with the turn of logs when going around sharp curves. Rubber- tired tractors are less damaging than crawler tractors. 117 LANDINGS 117.1 LANDING REQUIREMENTS. The landings to which logs are yarded for loading are of the greatest importance to the efficiency and safety of the operation. The side slope of the landing must be such that logs will not roll or slide when unhooked. They should be large enough that yarding output will not be restricted and logs will not have to be piled high, which would endanger men working on the landing. They should be well drained so mud does not accumulate and debris can be pushed away. Consequently, landings should be located on benches or ridges, not in draws. The yarding and leading method affect landing requirements. The larger shovel loaders require swing room of 60 feet between the center pin and the cut bank. Tree-rig booms may require more swing room. 117.2 HIGH-LEAD LANDINGS. The maximum side slope on a high- lead landing should not exceed 20 percent. The preferable landing circle radius is one and one-half the log length plus the road width. TiHiere the landing must be excavated on a steep slope, the minimum radius is the longest log length. Good guyline stumps must be available in a circle around the landing. If a satisfactory spar tree is not growing on the landing, a tree suitable for a ’’dummy’* for raising a spar tree is required. On steep slopes a stump above the landing can be used instead cf a dummy tree. Space for the yarder, clear of trucks and loader, with good visibility for the yarder operator is required. 117.3 TRACTOR LANDINGS. The side slope on tractor landings should not exceed 10 to 15 percent. The landing should be rectangular in shape and not less than 80 feet long and 40 feet wide on the side approached by the tractor roads. Efficiency in tractor logging is obtained only when the landing is wide enough that no tractor has to wait upon another to unhook the turn. The entering tractor road should be below the elevation of the unhook site so mud and water will drain off. 10 117.4 ROAD GRADIENT AT LANDING. The f»radient of the truck road at the landing should not exceed 5 percent. A gradient at 3 percent is preferable for truck maneuverability. The minimum gradient is 1 percent for drainage. 120 ECONOMIC CONSIDERATIONS 121 LOGGING COSTS 121.1 PLANNING DETERMINES COSTS. The primary objective of log- ging planning is to obtain the lowest logging cost consistent with other forest management objectives. Yarding and loading cost, spur road construc- tion cost and the off-highway portion of the trucking cost are directly af- fected by the logging plan. These items generally comprise 40 to 50 per- cent of the total logging cost. The importance of economic considerations Is evident when the work of the logging planner is reflected in activities which comprise half the logging cost. The most economical logging plan is that for which the combined yarding and loading costs and spur road costs per M board feet are a mini- mum. To achieve the most economical plan requires a knowledge of costs and the variable factors influencing cost elements. Road patterns and road spacing are also Important economic considerations. The costs given in Section H, Chapter III of the Timber Sale Procedure Handbook for stumpage appraisal are useful aids in planning. A file of output and cost data on local operations would be a helpful supplement. The logging planner should not neglect any opportunity to add to his file of local cost data. 121.2 COST CLASSIFICATIONS. Following are the standard classi- fications used in logging cost analysis. All costs are unit costs, l.e., cost in dollars and cents per unit of measurement, such as M board feet or cords. "Fixed per acre" costs are those which depend on the volume per acre and the acreage served. Examples are landing expense (moving and rig-up), high-lead road changing, and truck roads. "Fixed per turn" costs are those chiefly influenced by the size of the logs and the number of logs in the turn. "Yarding variable" costs are those chiefly Influenced by yarding distance and log size. This is the cost of the actual hauling- in of the turn of logs. Haul-back time is usually included with haul-in time for "yarding variable" cost even though the haul-back is affected only by distance. "Fixed per M" costs are chiefly Influenced by production over a period of time. Examples are overhead costs such as administration. Con- tract work at a rate per M board feet is a "fixed per M" cost, although the rate will be affected by log size. 11 121.3 HIGH-LEAD YARDING COST FACTORS. High-lead yarding costs in Che Douglas-fir region vary over a wide range of conditions of timber stand and topography. The following tabulation shows the factors influenc- ing the various elements of yarding cost for a given yarder and crew. Cost Classif ication Activity Factor Influencing Cost per M Increased by Fixed per acre Landing Expense Volume per acre Setting area Lighter volume Smaller area Fixed per acre Road changing Volume per acre Terrain Lighter volume Steep, brushy, etc. Fixed per turn Choker setting (hook) Turn size Log size Terrain Smaller turns Smaller logs Steep, broken, brushy, swampy Fixed per turn Chasing (unhook) Log size Turn size Landing Loading Smaller logs Smaller turns Poor landing Waiting on loaders (All of the above activities are influenced by labor efficiency. ) Yarding Mainl ine Turn size Smaller turns variable (haul-in ) Yarding distance Slope Topography Longer distance Steeper slope Broken Yarding variable Haul back (haul-out ) Yarding distance Longer distance "Fixed" costs are also Influenced by labor efficiency and "yard- ing variable” costs by yarder power and speed. In addition, as for all logging activities, the cost on net scale basis will depend on the differ- ence between net or ’’water" scale and gross or "woods" scale due to defect and breakage. The most important factors influencing yarding costs are log and turn size, yarding distance and volume per acre. The influence of steepness of slope is more noticeable with large logs or under-powered yarders. 121.4 HIGH-LEAD YARDING COST FORMULA. For the purpose of com- paring proposed settings, or the effect of changing boundaries of a set- ting, the following approximate formula for quickly estimating high-lead yarding cost is given. It is developed from the formula for estimating man-hours per M by Carow and Silen.C&Z) It is based on a labor cost equal to 70 per cent of the total current operating cost. Ownership costs are not included. 12 Yarding Cost per M 9 = L (1.07 + M ) VB Where L is the current labor cost in dollars per hour including social security, fringe benefits and industrial insurance; D is the average ex- ternal yarding distance in feet; S is the side slope in percent; V is M board feet per acre; and B is the size of the average log in board feet. The above formula is applicable only when the physical requirements of the high-lead method are adhered to in selecting setting boundaries. The "landing" cost per M (moving, rig-up and landing prepara- tion) must be added to ascertain the effect of the size of the setting. Landing Cost per M = Landing Expense Setting Area X Volume per Acre For more precise costs, see Section H, Chapter III, Timber Sale Proce- dure Handbook. 121.5 TRACTOR SKIDDING COST FACTORS. It is axiomatic that where conditions are suitable for tractors, tractor logging will be cheaper than high-lead logging. The factors influencing the various elements of tractor skidding cost per M for a given tractor are as follows; Cost Classif Icat ion Act ivlty Factor Influencing Cost per M Increased by Fixed per acre Bulldozing "cat" roads Volume per acre Slope Lighter volume Steeper slope Fixed per turn Hook Log size Turn size Volume per acre Smaller logs Smaller turn Lighter volume Fixed per turn Unhook Log size Turn size Landing Smaller logs Smaller turn Poor landing (delays) Variable skidding Haul -in Turn size Skidding distance Grade Smaller turn Longer distance Adverse grade Variable skidding Haul-out Distance Grade Longer distance Steeper grade (Costs are also influenced by labor efficiency and organization of the work to avoid losses in output due to delays.) 121.6 COMBINED YARDING METHODS. Where a steep slope adjoins a gentle slope, combined tractor and high-lead yarding to one landing will give a lower cost than the high-lead alone. The roads and landings are located along the lower edge of the gentle slope. The steep slope is high- lead yarded up and the gentle slope tractor yarded down. This combination of methods results in higher output by the loader and reduces loading cost. 13 9 The economic yarding distance of a high-lead may be extended and the output increased by "feeding” the high-lead with a tractor on suitable ground. The cost of the combined methods will be in proportion to the volume handled by each method and the respective yarding costs. 121.7 DECKING AND SWINGING COST FACTORS. Decking and swinging is economically justified only when the total cost per N of decking, swinging and loading is less than the combined cost per M of direct yard- ing and loading plus the cost of spur road construction to the landing at the deck site. When the deck site is inaccessible by road because of difference in elevation or other topographic obstacles, decking and swing- ing is the only alternative to leaving the setting. Increased use of rubber-tired tractors for swinging or roadlng in the future is anticipa- ted. Following are the possible decking and swinging combinations: high- lead cold deck and skyline swing; high-lead hot deck and tractor roading; tractor hot deck and wheel tractor roading; tractor hot deck and skyline swing. The high-lead may be used for short swings on favorable swing road profiles. Swings from hot decks are dependent on yarding output. Swings from cold decks are independent of yarding, so production will be greater. The fixed per turn costs of hooking and unhooking on skyline swings average about 85 per cent of high-lead fixed per turn costs. Swinging variable costs per station of skyline span average about one- third of high-lead yarding variable costs. The cost of rigglng-up a North Bend skyline is added to the swing landing expense. The expense of moving a tractor mounted triple drum, the machine commonly used for cold decking, plus the cost of bulldozing a tractor road to the cold deck site, is added to the cost of rigging a cold deck spar tree. In the absence of local cost data on tractor roading, it is suggested that 80 per cent of tractor skidding fixed per turn cost of hooking and unhooking be used for cost comparison purposes. Since tractor yarding is done on bulldozed roads, yarding variable cost may be used for tractor swinging variable cost. Variable roading cost per station will depend upon tractor travel time as determined by swing road gradient and alignment. This may be calculated by reference to handbooks published by tractor manufacturers. (3/ ) Otherwise, use available variable skidding cost per station for estimating comparative costs. The fixed per acre cost per M of bulldozing the tractor road will depend upon the amount of clearing and earth moving required and the volume on the hot deck setting. 121.8 LOADING COST FACTORS. The most important factor influ- encing loading cost per M board feet is log size. Since loading is a "dependent" activity, dependent on yarding, loading cost is also influ- enced by yarding output. Considerations in logging planning which affect loading cost are; yarder output as controlled by yarding distance; choice of landings to provide adequate log storage and boom swing room; landing side slope which will permit the loading crew to work efficiently and safely; and road gradient on which the truck can maneuver readily and safely. 14 From the formula for loading man-hours per M board feet in refer- ence (^/), the following approximate formula for loading cost is developed. It is based on a labor cost of 80 per cent of the total current operating cost . Loading Cost per M = L (22® - 0.47) B Where 1, is the current loading labor cost in dollars per hour and B is the average log size in board feet. The cost of loading from a skyline swing from a cold deck is less than the cost of loading on a yarder side due to the higher output. 121.9 LANDING COST FACTORS. The "landing" cost, also termed "rig-up" cost, is the sum of the costs per M board feet of the activities tabulated below together with the factors which influence them: Activity Factor Influencing Bulldozing landing Side slope (clearing and earthmoving) Size of landing Moving yarder or tractors and loader Distance to move Mobility of equipment Rigging spar tree Size of spar tree Raising or "jumping" spar tree Size of spar tree Distance to yard spar tree Placing brow logs Distance to move brow logs (Felling for guyline clearance generally is charged to felling and bucking.) The elements of landing expense over which the logging planner has control are the side slope and size of the landing (Section 118) and the spacing between landings which determines moving distance. Selecting a landing with a suitable spar tree has become unimportant with the preva- lent practice of raising spar trees to put them in the best position on the landing for efficient yarding. However, it is necessary to have a suitable "dummy" tree at the landing, except on steep slopes where the spar tree can be raised from a lead to a stump above the landing. Where port- able steel towers are used, no dummy is needed. The landing expense divided by the volume of timber on the set- ting gives the landing cost in dollars per M. The logging planner exer- cises the greatest influence on landing cost in the size of the setting. For this reason, in cost estimating for logging planning, the landing cost is allocated to yarding. 15 121.10 ROAD AND TRUCKING COST FACTORS. The factors influencing road construction and maintenance costs and truck travel time and log trucking costs are given in detail in Division 300, "Considerations in Road Engineering". Road construction costs per M board feet vary widely with topography and volume of timber tapped by the road. Determination of economical road standard is given in Section 312. Planning the logging roads on lands for which the Bureau of Land Management is responsible is often complicated by existing roads on adjacent private land. Many of the O&C sections alternate with private sections in a checkerboard pattern. In some cases the private sections have been logged. The existing roads require careful study and evaluation to ascertain whether they fit into the most economical road pattern for the BLM lands. Allowing existing roads on adjoining land to unduly Influence the logging planning for the BLM land may result in an inferior plan. Where an existing road is of a poor standard and inconsistent with the standard indicated for the BLM road from the standpoint of trucking cost and future maintenance, it is better to abandon the existing road. Where intermingled private lands have not yet been logged, every effort should be made to obtain coop- erative planning of the road system for the entire drainage. All owner- ships will benefit from such cooperation. 121.11 EVALUATING AN EXISTING ROAD. Following is a guide for evaluating an existing road to ascertain whether it is acceptable; 1. Standard of existing road for comparison with standard of proposed Bureau of Land Management road a. Width - surface and subgrade b. Gradient - maximum favorable and adverse c. Alignment - maximum degree of curve spacing d. Turnouts - on blind curves and turnout spacing 2. Condition of existing road a. Surfacing - depth sufficient (see Section 631); capable of being graded smooth b. Subgrade compacted - no further settlement anticipated c. Drainage - culverts and ditches adequate d. Bank slopes - angle of repose of soils reached e. Erosion - negligible 3. Volume of timber to be served by the road. If the volume is relatively small (under 2,500 M board feet) and the existing road is usable, it would be acceptable. 4. If the road is substandard, the feasibility of bringing it up to standard and the estimated cost. 16 9 An existing road may be considered to be "usable" if it does not exceed the following specifications: 1. Surface width 10 feet 2. Subgrade width 16 feet 3. Maximum degree of curve 95® 4. Turnout spacing 1000 feet 5. Drainage adequate to minimize danger of washouts 122 ROAD PATTERNS 122.1 ROAD PATTERNS. The road pattern which will give the least density of roads per section while maintaining optimum yarding dis- tance is the ideal to be sought. Keeping the density of roads to an eco- nomical minimum has initial cost advantages and future advantages in road maintenance costs and the acreage of land taken out of forest production. The road system for logging one side of a main drainage will usually be one of the following patterns: 1. A systematic pattern of regularly spaced parallel roads. On long side slopes they may be: a. Contour roads paralleling the main creek connected by a single climbing road on maximum grade. The contour road may follow a "grade-contour" of low per cent favor- able grade. b. Parallel climbing roads from a main road along the val- ley bottom. These roads usually switch-back from the main road but may take off in the same direction on steeper grades than the main road. 2. A systematic pattern of ridge and valley roads. This pat- tern is followed where side slopes are short and steep and the timber can be reached from two roads: one along the bottom of the valley and the other along the crest of the ridge. The connecting road is located where topography is the most favorable. 3. A random pattern of irregularly spaced roads. This pattern usually is the result of not planning far enough ahead to obtain' a systematic pattern. Road patterns are illustrated in Figure 122-1. 122.2 SYSTEMATIC CONTOUR ROAD PATTERN. The systematic parallel grade-contour road pattern is recommended where main drainage side slopes are long, requiring more than two levels of roads and are interspersed with benches or spur ridges suitable for landings. This is typical of the 17 FIG. 122-1 ROAD PATTERNS lA. PARALLEL CONTOUR ROADS. ONE CLIMBING ROAD 2. RIDGE AND VALLEY 3. RANDOM ROADS 18 Cascade Mountain range. Studies on 8807 acres of the H, J. Andrews Experi- mental Forest show that the systematic road pattern reduced the average density of roads per section from 5.59 miles of random pattern roads to 4.97 miles, a saving of 0.62 miles. The length of climbing roads in the 8 to 12 per cent range was reduced from 51.4 to 14.0 per cent. The area be- yond an external yarding distance of 900 feet was reduced from 19.0 per cent to 10.6 per cent. (7^/) A systematic road pattern requires long range planning of the road system for the entire drainage. 122.3 RIDGE AND VALLEY ROAD PATTERN. The ridge and valley road pattern is adapted to topography typical of areas of the Coast Range where side slopes of the main drainages are short and steep. Natural landings on the side slopes are lacking, and sandstone close to the surface of the steep slopes makes road construction expensive. The best landings and road construction conditions are on the ridges. However, to reach the ridges it is usually necessary to locate a road along the valley bottom until a point is reached where a climbing road can be located to a saddle from which ridge roads can branch out. Timber on the lower slopes has to be yarded to the valley road. 122.4 RANDOM ROAD PATTERN. The random pattern of roads is the least desirable since it usually results in greater road density, less optimum yarding, and complications in logging leave settings or other residual timber in the future. Random patterns are generally the result of short-range planning from setting to setting or from year to year. A random pattern tends to develop from a checkerboard pattern of land owner- ship. Coordinated planning between adjacent ownerships can avoid uneconom- ical random patterns. However, where natural landings are scarce or feas- ible road routes limited, the random pattern may be the only solution. 123 OPTIMUM ROAD SPACING 123.1 ROAD SPACING FOR HIGH-LEAD YARDING. Road spacing for high-lead yarding is determined by the applicable external yarding dis- tance and the topography. The position of suitable landings and setting boundaries will affect the spacing. The contour road pattern spacing usually is approximately twice the. external yarding distance, and logs are yarded downhill as well as uphill. Where the ridge and valley road pat- tern is used, the spacing is fixed by the topography. Random road pat- terns have little uniformity of spacing. Where the volume per acre to be yarded is lighter than usual, or road construction costs unusually heavy, it may be economical to increase yarding distance and road spacing. Al- though optimum road spacing computations ordinarily are not used in planning for high-lead yarding where unusual conditions are encountered, computing the optimum road spacing may furnish helpful guidance. 123.2 ROAD SPACING FOR TRACTOR SKIDDING. The optimum road spac- ing is achieved when variable skidding cost and spur road construction cost per M board feet are equal. For a given machine, skidding cost is affected principally by the size of the average log and the skidding dis- tance. The spur road construction cost per M varies with the volume per acre and the area served by a road, which is determined by the road spac- ing. The optimum road spacing for a given set of conditions may be found graphically by plotting a break-even chart. Figure 123-1 gives an example 19 of such a chart. The combined cost curve shows that costs are a minimum where variable skidding cost and road construction costs intersect, which is the break-even point. Other methods of computing optimum road spacing and instructions for their use are given in Chapter 240. 130 PROTECTION CONSIDERATIONS 131 FIRE PROTECTION 131.1 SETTING BOUNDARIES FOR FIRE CONTROL. For the control of slash fires or accidental fires in the clear-cut setting to protect the ad- joining uncut timber, the setting boundaries should be located where the fire line can be held best. Upper boundaries preferably are located along natural fire breaks such as ridge crests, rock ledges or outcrops, and roads. Natural fire breaks for lower boundaries include streams, valley bottoms, alder type lines and roads. Where natural fire breaks are not available for upper or lower setting boundaries, benches or the more gentle slopes offer a better chance for fire control than steep slopes. Side boundaries of settings on steep slopes should run at right angles to the contour. Fires tend to run up the slope parallel to such lines and are easier to control than where the cutting line angles across the contour. Draws are undesirable as side boundaries since slash tends to accumulate in the draws. 131.2 FIRE BUFFER BELTS. Where staggered settings are clear-cut along parallel roads, adjacent corners of such settings should be separated by a buffer belt of green timber. Such buffer belts should be wide enough to prevent fire from traveling diagonally from one clear-cut setting to another. The required buffer width will depend on slope and aspect and may vary from 150 feet in width on gentle north slopes to 500 feet on steep south slopes. If possible, the buffer belts should be situated so that they can be logged economically with the leave settings. Continuous clear cutting, leaving seed blocks as practiced on private land, requires special precautions to protect the seed blocks from fire. 131.3 SIZE OF CLEARCUT. The size of the clearcut area is relat- ed to the fire hazard. The larger the slash areas, the hotter the slash fire tends to become and the more difficult the fire control. Where the fire hazard will be high, as on slopes with southern exposure or where the road through the cut-over will be used by the public, smaller settings than would otherwise be cut are advisable. In planning the logging of a section of public timber adjoining a section in private ownership which has been clear-out to the section line, care must be taken to avoid developing large areas of contiguous slash. 132 PROTECTION FROM WIND DAMAGE 132.1 PHYSIOGRAPHIC FACTORS IN WINDTHROW. Serious losses from wind damage have occurred on the perimeter of leave settings adjacent to staggered clear-cut settings. Losses resulted mainly from breakage of trees. The storm winds which caused the greatest damage blew from the southwest quadrant (from S 20® W or S 33° W). Approximately 90 per cent of the wind- thrown trees were found on the north and east boundaries of clear-out set- tings. Windthrow was more severe on the ”lee" or sheltered side of a ridge 20 c FIG. 123-1 CHART FOR FINDING OPTIMUM ROAD SPACING SKIDDING DIRECT TO THE ROAD, FROM BOTH SIDES, FOR LOADING BY MOBILE LOADER. VARIABLE SKIDDING COST $0.40 PER M BD. FT. PER STATION ROAD CONSTRUC- TION COST $38.00 PER STATION. VOLUME PER ACRE CUT 12 M BD. FT. BREAK-EVEN POINT AT 11.8 STATIONS = OPTIMUM SPACING. 21 9 FIGURE 132-1 Relative Susceptibility to Windthrow: Medium @ Little ® Minimum ^ Maximum FIGURE 132-3 Distribution of Age Classes at the End of the First Rotation, Progressive Strip Cutting. 22 than on the "windward" or exposed side. This is accounted for by "lee flow" or the tendency of wind blowing across a ridge to follow down the slope with increased velocity. (Figure 132-2) The upper third of the lee slope is the most vulnerable. Trees on small ridges or flats in the lee of a higher ridge are susceptible to windthrow. Wind velocity is accelerated by funneling through saddles or gaps in ridges, through narrowing valleys and through constricted openings or indentations cut in the stand. Trees ad- joining and in the lee of such funnels are endangered. Relative suscep- tibility to windthrow of setting boundaries is shown in Figure 132-1. Study of the following windthrow references is recommended: Hunt (8/), Gratkowskl (9^/ ). 132.2 EDAPHIC AND BIOLOGICAL FACTORS IN WINDTHROW. Trees grow- ing on shallow soils overlaying rock or impermeable clay or on poorly- drained soils, are shallow-rooted and very susceptible to windthrow. Skunk cabbage is an indicator of a high water table. Flats or benches at the foot of steep slopes, while appearing dry in the summer, may be saturated in the rainy season. Trees infected with root rots or butt rots are pre- disposed to windthrow. Poorly stocked or open stands generally are more windfirm than dense stands. Young stands usually are more windfirm and develop windfirmness faster with exposure than old stands. Hardwood stands or mixed stands of hardwood and conifers generally are wind-resistant. 132.3 SELECTION OF WINDFIRM SETTING BOUNDARIES. Consideration of the factors in windthrow indicates that wind damage can be minimized by selection of windfirm north and east boundaries of clear-cut settings. Windfirm borders are found on the windward side of ridges, on well drained deep soils, and in sound trees. Type lines of hardwoods or mixed hardwood and conifers, younger stands or open stands also present windfirm borders. Boundaries running parallel to storm wind direction are relatively safe. Avoid cutting boundaries on the lee side or crest of a ridge, on poorly drained or shallow soils, or in stands showing evidence of root rot or butt rot. Setting boundaries in the lee of natural wind funnels and V-shaped indentations in cutting lines are to be avoided. Where feasible, start cutting in the northeasterly portion of the logging unit and proceed in a southwesterly (windward) direction. 132.4 PROGRESSIVE STRIP CUTTING. Where wind damage is an ap- preciable hazard, progressive strip cutting in the direction of the storm wind merits consideration. Ruth and Yoder (I0/)recommend a logging plan for progressive strip cutting in which the first cut is made in alternate clear- cut areas along the north boundary of the logging unit in the lee of the main east-west ridge. The second cutting sequence would take the leave areas, resulting in a long clear-cut strip. Strips would be cut in stag- gered settings along successively higher road levels up the lee slope of the main ridge and along successively lower levels down the windward slope. (Figure 132-3) 133 WATERSHED AND STREAM PROTECTION 133.1 FACTORS IN WATERSHED DAMAGE. Watershed damage embraces injuries to soil and water resulting from road building and yarding. Soil is disturbed by loosening and displacement or by compaction which decreases permeability. Increased surface runoff and erosion of the soil ensues. 23 Eroded soil carried into the streams is injurious to fish life and dimin- iches the water storage capacity of reservoirs. Logging slash in streams may be harmful to fish and cause downstream flood damage. The relative erosion hazard varies from "high" on light textured soils on steep slopes to "low" on heavily textured soils on gentle slopes. (Soil classifications are given in Division 600, Soil Engineering). Roads are the main factor in soil movement and stream siltation. The logging method is also a fac- tor in erosion. Tractor skid trails on steep slopes tend to become gul- lies. Steinbrenner and Gessel found that soils on tractor skid roads in southwestern Washington lost 93 per cent in permeability and 53 per cent in microscopic pore space and increased 15 per cent in bulk density. (11/) The location of landings is an important factor in watershed protection. (Section 117) 133.2 WATERSHED PROTECTION-CABLE LOGGING. Care during road con- struction and logging and post-logging treatment are the most important elements in watershed protection. However, protection begins with the choice of cutting system and logging method. Moving cable methods are pref- erable to tractor logging on erosible soils on steep slopes. Clear-cut setting areas should be smaller than settings on stable soils. High-lead yarding uphill disperses the runoff along the yarding-road trails which fan out below the landing. Downhill yarding trails converge and concentrate the runoff. Landings on dry ridges or benches cause less damage than land- ings in draws or valleys. Where the terrain necessitates downhill yarding, skyline methods are preferable to the high-lead. Where partial cutting is the prescribed silvicultural system and steep slopes and erosible soils make tractor skidding objectionable, the new skyline methods developed for the pine region are indicated. (Article 112.2) 133.3 WATERSHED PROTECTION-TRACTOR LOGGING. Where tractor skid- ding is unavoidable in areas of high erosion hazard, the main tractor trails should be planned and marked on the ground. Important points in tractor trail location to minimize erosion include; grade breaks at inter- vals to avoid long sustained grades; crossing streams on gravel or rock beds; and avoiding trails along the bottoms of ravines or draws. Since soil disturbance is proportional to intensity of cut, light partial cuts are advisable. In some cases restriction of operations to the dry season may be desirable. A valuable guide to erosion reduction in tractor logging is reference (12/) • 133.4 STREAM PROTECTION. It is becoming increasingly incumbent upon the logging planner to consider the protection of streams in the interest of downstream users. Downstream interests include fishing, recre- ation, water storage reservoirs for irrigation, hydroelectric power or mu- nicipal water supply, and riparian structures. They are adversely affected if logging results in sedimentation, flood debris and channel changes. Stream protection requires locating roads well back from main creek chan- nels. Landings and setting boundaries are selected so that logs will be yarded away from fishing streams, not across them, and slash will not accu- mulate in streams. Natural filter strips are left between creeks and roads or cutting lines to filter the sediment carried by water flowing from dis- turbed areas. Observation of creeks below existing roads during heavy rains will Indicate the width of filter strip required in a given locality. The width of strip required increases with steepness of slope. Trimble 24 and Sartz (13/) recommend 2 feet of width for each 1 percent of slope added to a base width of 25 feet in northern hardwoods. Other stream protection considerations in road location are given under "Forest Road Engineering." 134 PROTECTING RECREATIONAL VALUES 134.1 SCENIC STRIPS. Where recreation is an important forest use, consideration of the viewpoint of the recreationist is important from the standpoint of public relations. The sight of cut-over land and particularly of slash-burns is offensive to many people who do not appre- ciate the economic contributions made by the timber harvest. It may be advisable to leave a scenic strip of natural forest between a main road and a cutting line. The scenic strip should be wide enough so that the cut-over cannot be seen from the road. Spur roads should leave the main road on a curve so that the traveler on the main road cannot see along the spur road clearing into the logging area. The protection of fishing streams also contributes to the protection of a recreational resource. 140 SILVICULTURAL CONSIDERATIONS 141 CLEAR CUTTING 141.1 PROVISION FOR REGENERATION. Forest management in the Douglas-fir region begins with the conversion of the natural old-growth forest to a managed second-growth forest through the logging of the old- growth. The provisions made in the logging plan for securing regenera- tion of the cut-over land affect future forest management. The silvi- cultural systems applicable to the lands managed by the Bureau of Land Management in Oregon are covered in detail in the Forest Management Handbook. They are referred to here only briefly as a reminder to the logging planner and to Insure that silvicultural considerations are not overlooked. Generally the silvicultural system to be followed will be determined prior to the inception of planning as a matter of policy by the district manager, or unit forester. In some cases study of the log- ging unit may Indicate the desirability of recommending a change in the customary system. 141.2 STAGGERED SETTINGS. Clear cutting by "staggered set- tings," also termed "patch cutting" or "area selection cutting," is the system currently favored in the Douglas-fir region by the Bureau of Land Management. The areas of the clear-cuts vary from 20 to 80 acres and are commonly 30 to 40 acres. Current policy is to limit the size of setting to a maximum of 60 acres. Areas larger than 40 acres require two landings. One or more economic settings are left between clear-cuts. Advantages of the system include the following: the logged area is surrounded by seed source for natural regeneration; the seed trees are within seeding distance of any part of the setting; areas to be slash- burned or to be protected if slash is not burned, are isolated and rela- tively small. Disadvantages of staggered settings, as compared with contin- uous clear cutting include: the high road construction cost per M board feet for the first cutting cycle, since at least twice as much road is required for 25 the same volume of production; longer moves of yarding and loading equip- ment between settings; and more perimeter exposed to windthrow. Windthrow losses along the borders of staggered settings in some localities have been alarming. Natural regeneration has not always been entirely satis- factory, particularly on exposed south slopes. The patch cutting system is especially well adapted to forests where patches of over-mature, diseased, or heavily wlndthrown timber are intermingled with thrifty timber; or patches of older age classes alter- nate with younger age classes; or where the windthrow hazard is not high. The size of the clear-cut will depend upon the timber stand, the topog- raphy, the regeneration probabilities and the volume of timber necessary to obtain an economical road construction cost. 141.3 PROGRESSIVE STRIP CUTTING. Clear cutting successive set- tings in long strips along a road, leaving uncut belts of timber of setting width on both sides of the strip, appears to be gaining in favor where the windthrow hazard is high. (Section 132) The width of the strip is ordinar- ily the width of a setting or twice the external yarding distance. It has the advantages over the staggered setting system of reducing the perimeter subject to windthrow, having only one north or east boundary exposed to the wind, reducing the length of road required in the first cutting sequence by one-half, and shortening the moving distance between landings. Disadvan- tages Include large areas of slash and seed source on only two sides of the clear-cut. The progressive strip system is still experimental so far as the success of natural regeneration is concerned. This system is adapted to uniform stands over large areas; to relatively low volumes per acre where road construction costs are high; and where windthrow is a serious problem. The system is well suited to long slopes where the systematic parallel road pattern is feasible. Strips would be cut along alternate roads in the first cutting cycle. The width of the strip is determined by economic road spacing. A modification of this system is cutting alternate settings along the strip in the first cutting sequence and taking the leave settings in the second cutting sequence. (Article 132.4) 141.4 GONTINUOUS GLEAR CUTTING. Continuous clear cutting, leav- ing blocks of trees to provide a seed source for natural regeneration, is the system commonly used on private land in the Douglas-fir region. While this system is not used on O&C lands, it must be recognized that it is the prevailing system on intermingled private lands. This may affect logging plans on O&C lands. The success of the system depends upon the location of the seed blocks and their survival from slash fire and windthrow. 142 PARTIAL CUTTING 142.1 PARTIAL CUTTING IN PINE. Partial cutting or tree selec- tion is the accepted system in ponderosa pine and other uneven-aged forest types. The marking policy is usually specified prior to the inception of the logging plan. The volume per acre to be cut is an important consider- ation in planning the roads. For marking rules and further Information on partial cutting, refer to the Forest Management Handbook. 26 142.2 PARTIAL CUTTING IN DOUGLAS-FIR. Partial cutting in Douglas-fir is limited to thinnings in second-growth stands and to pre- logging and salvage in old-growth stands. Thinnings from immature stands may be "from the bottom" to remove suppressed, poorly-formed trees and dying trees for pulp-wood, small saw logs, smelter poles, etc. Thinnings "from the top" are made to obtain merchantable saw logs, poles or piling from the larger dominant or codominant trees. Such thinnings are more apt to pay for the roads, which is the major economic problem in thinning operat ions . "Pre-logging" is the removal from settings to be clear-cut of the smaller understory trees which would be subject to breakage if logged with the larger overstory trees. Pre-logging of trees attacked by in- sects has also been done. On ground unsuitable for tractors, pre-logging is done by high-leading with a portable steel tower or with a mobile com- bination yarder-leader . Salvage logging removes the scattered dead or dying trees and windfalls in old-growth stands, usually from the reserve settings which are accessible to roads. A detailed study of such logging on an experi- mental salvage sale has been published by Carow.(4/) Pre-logging of the white fir from a Chermes- inf ested forest has been successfully accom- plished with the use of portable steel towers. 143 PRIORITY SEQUENCE OF CUTTING 143.1 PRIORITY IN CLEAR CUTTING. An important consideration in the selection of clear-cut settings is the reduction of loss of mer- chantable volume from decay and mortality. It requires the annual growth of many acres of second-growth to make up for the loss of one old-growth tree. Where variation in conditions of health and vigor are found over an operations unit, settings should be selected so that cutting can pro- ceed in priority sequence as follows; 1. Dead or dying stands containing windthrown, fire-killed or insect-infested trees. 2. Over-mature, decadent or diseased stands. 3. Mature stands on the steeper slopes. The object is to leave the reserve settings on more gentle slopes where they can be more easily salvaged. 4. Other mature stands. The lesser-sCocked open stands are generally more windfirm and more apt to survive as leave settings than dense stands. In stands where conditions are uniform over large areas, the settings which will best facilitate construction of the permanent roads desired for fire protection, administration, etc. have priority for the first cutting sequence. 27 9 143.2 PRIORITY IN PARTIAL CUTTING. The basis of marking individ- ual trees in ponderosa pine is the chance of survival until the next cutting cycle. In addition to trees which have already been attacked by bark bee- tles or by mistletoe, the high-risk trees under Keen’s classification, which are susceptible to beetle attack, are marked. These are also likely to be the trees of slower growth rate. In selecting areas to be logged, those carrying the higher proportion of beet le- inf ested and high-risk trees have first priority. In thinning immature Douglas-fir, first in priority is the re- moval of the suppressed, stagnated and slow-growing trees and those which will probably die before the next cutting cycle. Salvage logging in old- growth Douglas-fir removes only the dead or dying trees, snags and wind- falls. 150 OTHER CONSIDERATIONS 150.1 SAFETY CONSIDERATIONS. By his selection of landings and setting boundaries and location of roads with the safety of the workers in mind, the logging planner can contribute to the safety of the logging oper- ation. Safety is an economic as well as humanitarian consideration because of the high cost of industrial Insurance in logging. Safety can be engi- neered into the logging operation. (1./) The logging plan which meets the test of all other considerations is still not the best plan if it can be changed to make the operation a safer place for men to work. 150.2 CONSIDERATION OF FIXTURE CUTS. In his preoccupation with the take settings for the first cutting sequence, the logging planner may neglect consideration of the logging of the "leave" settings of the staggered setting system. It can be argued that future changes in logging machines and methods may make the long-range logging plan obsolete. How- ever, this does not condone leaving settings which do not meet the physi- cal and economic requirements of present logging methods. Of particular importance is consideration of salvage of possible wlndthrow or slash-flre- killed timber on the borders of the leave settings. Even though actual landings may not be available, reducing the gradient of the road at inter- vals to permit salvage yarding and loading with mobile machines is desir- able. The long-range logging plan which considers the logging of the entire drainage is likely to obtain better results throughout the cutting cycle than the short range plan for the current cutting sequence. The ideal to be sought is to know how the last setting in a logging unit will be reached before the first setting is sold. 28 o BIBLIOGRAPHY 1. Pearce, J. Kenneth, Cable Logging Systems, Skagit Steel and Iron Works, Sedro-Woolley, Washington, 10 pp. gratis 2. "Tractor Logging," 16.30 - 16.41, Forestry Handbook, Society of American Foresters, Ronald Press, New York, 1955 3. Logging, Allis-Chalmers Manufacturing Co., Milwaukee, Wisconsin, gratis 4. Carow, John, Yarding and Loading Costs for Salvaging in Old-Growth Douglas-fir with a Mobile High-Lead Yarder, Research Paper 32, Pacific Northwest Forest and Range Experiment Station, Portland, Oregon, July 1959 5. Worthington, Norman P. , Skidding with Horses to Thin Young Stands in Western Washington, Research Note No. 138, Pacific Northwest Forest and Range Experiment Station, Portland, Oregon, February 1957 6. Carow, John and Silen, Roy R., "Using the Staggered Setting System What are Logging Costs?", The Timberman, 58(48) :48-53, 1957 7. Silen, Roy R., "More Efficient Road Patterns for a Douglas-fir Drainage," The Timberman, 56(6);82, 85-86, 88, 1957 8. Hunt, Lee 0., Analysis of Factors Causing Windthrow, Bureau of Land Management, Oregon State Office, Portland, Oregon, May 1, 1953 9. Gratkowski, H. J., "Windthrow Around Staggered Settings in Old-Growth Douglas-fir," Forest Science, 2(l):60-74, March 1956 10. Ruth, Robert H., and Yoder, R. A., Reducing Wind Damage in the Forests of the Oregon Coast Range, Research Paper 7, Pacific Northwest Forest and Range Experiment Station, Portland, Oregon, July 1953 11. Steinbrenner, E. C. and Gessel, S. P. , "Effect of Tractor Logging on Soils and Regeneration in the Douglas-fir Region of Southwest Washington," Society of American Foresters. Proceedings 1955, pp. 77-80. 12. A Guide to Erosion Reduction on National Forest Timber Sale Areas, California Region, U. S. Forest Service, San Francisco, California 13. Trimble, G. R. Jr., and Sartz, R. S., "How Far From a Stream Should a Logging Road be Located?", Journal of Forestry, 55(5), May 1957 29 CONTENTS Page <9 200 LOGGING PLANNING 210 PREPLANNING ACTIVITIES 32 211 Basic Data Acquisition 32 .1 Policy instruction, .2 Data to assemble, .3 Bureau of Land Management maps, .4 other maps, .5 Aerial photographs, .6 Land surveys, .7 Route surveys, .8 Timber data, .9 Reconnaissance notes. 212 Preplanning Reconnaissance 35 .1 Reconnaissance required, .2 Recon- naissance for photogrammetr ic planning. 220 LOGGING PLAN MAPPING 221 Logging Engineers Method 37 .1 Advantages, .2 Base lines, .3 Strip lines, .4 Topography, .5 Cruising, .6 Map compilation. 230 PLANNING FOR SKYLINES 231 Deflection and Tension 38 .1 Importance of deflection, .2 Deflec- tion chart, .3 Computing tension. 240 OPTIMUM ROAD SPACING 241 Methods of Computing 41 .1 Factor method, .2 Ratio method. 250 PLANNING ON LARGE SCALE MAPS 251 Douglas-fir Region Planning 44 .1 Planning procedure, .2 Priority areas, .3 Trial landings, .4 Trial roads to landings, .5 Road projection, .6 Cold decks and swings, .7 Setting boundaries, .8 Field checking, .9 Final plan. 252 Pine Region Planning 46 .1 Planning for tractor skidding, .2 Steps in planning, .3 Planning for cable logging. 30 9 260 PLANNING ON PRECRUISE MAPS 261 Douglas-fir Region Planning 47 ,1 Planning procedure, .2 Field check, ,3 Correcting the precruise map. 270 PHOTOGRAMMETRIC PLANNING 271 Douglas-flr Region 47 .1 Use of aerial photos, .2 Prepara- tion of photos, .3 Landings, .4 Roads, .5 Settings, .6 Field check. 272 Pine Region 48 .1 Utility of photos. 280 FIELD LAYOUTS 281 Setting layout in Douglas-flr 49 .1 Landings, .2 Setting boundaries. BIBLIOGRAPHY 49 FIGURE 231-1 Deflection Chart 36 31 200 LOGGING PLANNING 210 PREPLANNING ACTIVITIES 211 BASIC DATA ACQUISITION 211.1 POLICY INSTRUCTIONS. T■ ..* *>*'/*^* " •"iV • i <1 '*• V "f «r.’ c ( FIG, 3II.I U. S. DEPARTMENT OF THE INTERIOR BUREAU OF LAND MANAGEMENT CLASS m ROAD TYPICAL CROSS SECTION needed to keep spacing below 750' iO fi more then normal width require 1564 cubic yards per mile per foot of surfacing depth more than a Class III road. Apply rock costs from Chapter Ill-H, Timber Sale Procedure Handbook. 2. Road Maintenance Cost. The annual cost per mile of road maintenance is best obtained from local experience on com- parable roads. Maintenance cost tends to increase on steeper grades and sharper curves. It is also affected by volume of traffic. 312.2 LOG TRUCKING COST DATA. The average cost per round-trip of mile of hauling logs over the road is required. From the road design from a P-line, truck travel time may be calculated accurately using the data in reference (^/ 3. From the same reference, the cost of truck oper- ating time per minute plus the cost of tires per mile can be used to find hauling cost. Apply the current cost index to bring costs up to date. If the trucking cost estimate is based on a reconnaissance line or a route projection, the tables given in Section 331 will enable com- parative travel time on roads of various standards to be computed. For empty truck Increase travel time 1.5 percent for each five vehicles of traffic per hour for waiting at turnouts. Convert travel time to cost by applying the best available truck operating cost data. If it appears that travel time on a segment of road will be controlled by gradient, use Table 331-1 or 331-2. If curvature will control, use Table 331-3 or 331-4. 312.3 ANNUAL COST FORMULA. The determination of the most eco- nomical road standard is based on a comparison of combined annual costs of road construction, road maintenance and log trucking. The formula for annual cost is: A = R + I+ M + T Where A is total annual cost in dollars per mile; R is the annual cost of road construction for the amortization period; M is annual road mainte- nance cost per mile; and T is average log trucking cost per mile for the annual log volume to be hauled out over the road. Example: Assume the following costs have been estimated for three classes of road. Annual volume, 10 million board feet. ROAD CLASS I II III Construction Cost per Mile Maintenance Cost per Mile Trucking Cost per M Bd. Ft. per Mile Trucking Cost per Annum Per Mile $40,000.00 300.00 .25 2,500.00 $22JG00?00 400.00 .30 3,000.00 $15$000100 500.00 .35 3,500.00 Assuming an amortization period of 25 years, the annual rate R is 4 percent of construction cost. Assuming an interest rate of 3.5 percent, average annual Interest rate is 1.75 percent. 55 ROAD CLASS I II III R I M T $1,600.00 700.00 300.00 2.500.00 $ 880.00 383.00 400.00 3,000.00 $ 600.00 262.00 500.00 3,500.00 A $5,100.00 $4,663.00 $4,802.00 Therefore, the Class II is the most economical by a margin of $199.00 less than Class III, and over the period of 25 years the margin in favor of the Class II road is $4,975.00 per mile. If various segments of a road will serve differing volumes of timber, calculate the annual cost for each segment separately. 312.4 FORMULA FOR ANNUAL VOLUME FOR EQUAL COSTS. Another method of determining the most economical of two standards of roads is to calcu- late the annual volume "V” in M board feet at which the annual costs of the two roads will be equal. Then if the annual volume will be greater than "V”, the higher standard of road will be justified; if lower than ”V*', the lower standard is indicated. The break-even volume formula is: V = (Rh ^h ^h^ ^ ^^1 ^1 ^l) Where the subscript "h” Indicates the higher standard road and the subscript ”1" the lower standard road, T is in $ per M per mile, and the other symbols are those used in Article 312.3. Example: Using the same costs as in the example in 312.3 for Class II and III roads: (880 + 383 + 400) - (600 + 262 + 500) .35 - .30 = 1663 - 1362 = 301 = 6020 M board feet .05 .05 Therefore, for any annual volume exceeding 6,020 M board feet, the Class II road is the more economical, for the cost data used. For any lesser volume the Class III road is the more economical. If there is a difference in the lengths of two roads, multiply the costs per mile by the number of miles of road for use in the formula. 56 312.5 TRAFFIC DENSITY. The capacity of a given road may be computed from the following formula: Number of Vehicles per Hour = 5280 x Speed In Miles per Hour Interval between Vehicles In Ft. For a single-lane road with turnouts the capacity Is determined by the average speed of the empty truck which waits at the turnout for the loaded log truck to pass. The minimum Interval Is the turnout spac- ing. Application of this formula will show that the capacity of the single-lane road Is adequate to handle the volume of log truck traffic plus crew, supervisory, administration and service vehicles. In most slt- uat Ions . Whether a two-lane road Is required Is determined by the traf- fic from public use, l.e., recreatlonlsts, miners and farmers. If heavy public use of the road Is anticipated, a traffic count on a comparably situated existing road will serve as a guide to the number of vehicles per hour of non-logging traffic. In view of the Increasing pressure on forest recreation facilities. It would be well to count on recreation traffic Increasing In the future. 312.6 ECONOMIC ANALYSIS FOR CLASS III ROAD GRADIENT. The formulas given In Articles 312.3-312.4 may also be used In making the economic analysis required to justify Increasing the gradient of a Class III road above the standard maximum of 10 percent. (Article 312.1) In this case the subscript "h” represents the 10 percent maximum road, and the subsequent "1" the steeper gradient road. If the steeper road will be shorter than the 10 percent road, multiply ”R", "I”, ”M" and ”T” per mile by the length of each road In miles before entering In the formulas. The round trip travel time for each of the two gradients may be taken from Table 331-1 or 331-2 or reference (^Z). Note the effect of curvature on travel time and costs In Tables 331-3 and 331-4 and adjust **T” where controlled by curvature. 312.7 IMPROVEMENT OF EXISTING ROAD. Where a sub- standard existing road on Intermingled private land Is to be made a segment of a permanent Bureau of Land Management road, the problem arises of deter- mining the economics of Improving the existing road to a higher standard. If time does not permit traversing and leveling to obtain a plan and pro- file, drive over the road taking odometer and altimeter readings at breaks In grade. Note any curves which reduce speed below that limited by the gradient . Following Is a rapid method of measuring the degree of curve. Lay off a chord of 62 feet by stretching a 100 foot tape along the edge of the road surface with the zero and 62 foot marks, touching the edge of the surface. Measure the middle ordinate In Inches from the 31 foot mark to the surface edge. The middle ordinate In Inches equals the degree of curve. A folding carpenter’s rule Is a convenient tool for measuring the middle ordinate. Note other conditions outlined In Article 121.11, "Evaluating an Existing Road." If possible, make a stop-watch time study of log truck travel time over the road. Otherwise draw a 57 9 rough profile of the existing road from the odometer-altimeter readings and calculate the log truck travel time. Estimate the cost of improving the existing road to the standard of the road to be built on federal land. Compute the comparative annual costs of using the existing road and the improved road by the formula in Article 312.3. Another approach is to use the break-even formula in Article 312.4 to determine how much can be expended in improving the road to maintain annual costs at the same level as with the unimproved road. With this expenditure the benefit would accrue to public use rather than to the timber. Any less expenditure would benefit the timber. Set up the break-even formula in the following form; h + «h • + V (T^ - T^) Allowable Expenditure = Rj^ - Mj^ If the construction cost for the higher standard is less than the allowable expenditure, savings will accrue. 320 CONSIDERATIONS IN ROUTE SELECTION 320.1 COST. The basic consideration in selecting the route for a road, as in all phases of road engineering, is cost. The cost of initial construction, the cost of future maintenance and the cost of operating ve- hicles over the road are dependent on the route. In this chapter are given the broader considerations which the road planner should bear in mind in seeking the route which will best serve the purposes for which the road is to be built. Most of the considerations affect costs. By "route" is meant a road line such as is projected on a map or aerial photograph or a recon- naissance or grade line run in the field. It represents a narrow belt of land within which minor variations in gradient or alignment may be made during the preliminary or final location survey. The more detailed con- siderations for the road engineer to bear in mind in locating the road on the ground after the route has been selected are given in Chapter 330, "Considerations in Road Location." Parts of Chapter 330 are also germane to route selection. 60 9 321 SECONDARY ROADS 321.1 TliE LOGGING PLAI>. The routes of the secondary roads con- sisting of the spur roads to landings and the lateral or branch roads con- necting the spurs with the main road are dictated by the logging plan. Road patterns and road spacing are covered in Chapter 120, "Economic Con- siderations." It cannot be over-emphasized that the roads and the yarding are Interdependent and must be integrated. The logging plan must be feas- ible for economical road construction and log truck operation. The roads must serve the landings and economical yarding distances. Compromise is often necessary to arrive at the minimum total combined cost of yarding, trucking and roads with due regard to protection and silvicultural con- siderations. (Chapters 130, 140) 322 MAIN ROADS 322.1 THE SECONDARY ROAD PATTERN. If a main forest road is to be built primarily for hauling logs, then the first consideration in selecting the route of the main road is to serve the secondary branch and spur roads. The main road route should reach suitable junction points where there is room for the branch roads to turn off from the main road. Such junction points include flats, benches, and saddles where there is space for the double width required for grade separation without exces- sive excavation. If the branch road gradient is steeper than that of the main road, adequate length is required for an easy vertical curve. The junction should be staked and constructed to the point where the branch road subgrade clears the main road at the time the main road is built. The route which will give the minimum combined hauling distance over secondary and main road from the center of gravity of the timber volume will generally be the most economical route. 322.2 THE TOPOGRAPHY. The topography often will determine the selection of the route for a main road. Since the main road usually fol- lows up the main drainage paralleling a sizeable stream, the route possi- bilities which may he encountered with their relative advantages and disadvantages follow: 1. Wide valley bottom. This condition affords the advantages of a water gradient, good alignment and relatively low earthwork yardage. Good landings are available for set- tings to be logged along the route. Disadvantages are flood hazard and the cost of bridges to maintain good alignment and to avoid rock cuts if the stream meanders. Protection of recreational resources, such as camping sites and fishing streams, requires special considera- tion. Stream channel changes are objectionable to fisheries agencies. 2. Narrow valley bottom. This condition offers a water gradi- ent and advantages over a hillside route of less excavation and better alignment, since the mouths of side streams usually can be crossed on tangents with fills. Fewer but larger culverts may be needed. Disadvantages are flood hazards, bridges when it is necessary to cross the stream 61 to avoid rock cuts or sharp curves, and the difficulty of avoiding interference with the stream channel. 3, Hillside route. Locating a main road on the hillside well away from the creek will eliminate flood hazards and creek damage. Bridges are usually eliminated since side streams can be crossed with fills and culverts. Steeper and more variable gradients are often required. Alignment on the hillside route is poorer since the route following the grade contours around ridges and draws. This also makes the road longer. Excavation is heavier as the side hill is steeper than the valley bottom. Take offs for branch or spur roads are more difficult. Higher cut banks expose more soil to erosion. 4. Ridge crest. A ridge crest route offers the advantages of good alignment, light excavation, good drainage and few cul- verts. If the ridge profile is uneven, more adverse pitches are encountered, although the possibility of making them momentum grades is good. (Article 331.3) The principal disadvantage is that a main road above the bulk of the timber necessitates adverse grade spurs. A hillside segment of road is required to reach the ridge, and total length of haul may be longer. 322.3 TWO- DIRECTIONAL HAULS. The possibility of the main road being used to haul timber in opposite directions should be considered. The successful bidder on a timber sale may haul up the valley and over the divide to a log market in the opposite drainage. In this case the favor- able grade down-valley becomes an adverse grade for up-valley hauls. If the possibility of two-directional hauls exists, all grades should be limited to the allowable adverse grade for the road class. 322.4 EDAPllIC CONSIDERATIONS. Geology and soils are important factors in road construction and maintenance costs. All available geolog- ical and soils information along routes under consideration should be col- lected. An example of the value of geology in route selection is in the angle of the strata in deciding which side of the valley will give the most stability. Cut slopes paralleling the strata will be more subject to slides. The route which encounters more of the granular soils is the preferable route from the standpoint of construction and maintenance. The route which results in the least soil disturbance and which avoids the more eroslble soils will minimize erosion and water damage. Slide or slump areas and swamps are to be avoided. Routes through shallow or poorly drained soils will be subject to the hazard of windfalls from the trees along the edges of the road right-of-way clearing. Soils in road design and construction are covered in detail in Division 600, "Soil Engineering." 322.5 MA.I0R CONTROL POINTS. The major control points are very important considerations in route selection. Following are possible control points to look for; 62 c 1. Terminal Control Points a. The beginning of the route, usually the junction with an existing road. b. The end of the route. This may be the last point from which spur roads will branch off, the pass at the head of the valley, or a junction with another existing road. Or it may be the end of the current project from which the road can be continued as a later project. The feasibility of the continuation route must be assured. 2. Intermediate Control Points a. Saddles or passes in ridges. b. Stream crossings where streams narrow, suitable for bridges or fills and culverts. c. Benches suitable for branch or spur road junctions or for landings. d. Points to safely cross above or below cliffs or rock outcrops, slides and swamps. e. Recreational sites such as camping sites, parking sites, and scenic viewpoints. f. Crossings of county roads, railroads or farms out- side the forest. 322.6 ASPECT. A road along a slope with a southerly aspect will get more sunshine and dry out faster after a rain. Consequently, it will be subject to less damage from traffic and result in lower main- tenance cost. Other factors being equal, a route on the north side of an east-west valley is preferable to one on the south side. On a north-south valley, the side which will get the most sunshine is pre- ferred. 322.7 TRUCK PERFORMANCE. The person engaged in the selection of road routes should be cognizant of the effect on truck travel time of gradient and curvature. Tables 331-1 and 331-5 give speeds and round trip travel time for conventional highway trucks. If off-highway trucks or trucks with other horsepower -weight ratios are to be used, their performance can be obtained from the charts in reference (^/). Among practical points to remember, the following are suggested: Flatten the grade at intervals on a long sustained favorable grade to allow release and cooling of the brakes. Avoid frequent changes of grade on adverse grades which necessitate changing gears with consequent shock to the truck power train. When changing to a steeper grade, reduce the lesser grade 1 or 2 percent for a station to facilitate gear shifting. 63 In running a tag line or projecting a grade line on a map for the maximum permissible adverse gradient, keep 1 or 2 percent under the maximum to allow for slackening of grade on curves. 322.8 ALTERNATE ROUTES. The best route will seldom be selected if the road planner stops with the first and, to him, most obvious route. Particularly in running reconnaissance lines in the field there is a temp- tation to give up too easily and accept the first or second trial as "good enough." The high investment in a main road and the years it will be used warrants taking the time to study alternate routes. The planner should be able to substantiate his final selection by comparison with alternate routes he has considered. The comparison should Include truck travel time as well as construction cost. The Bureau of Land Management policy of making a timber sale acces- sible to more than one market outlet, wherever possible, makes it incumbent on the road planner to consider alternate routes to alternate marketing centers as well as alternate routes to any one market. 322.9 ECONOMIC ANALYSIS OF ALTERNATE ROUTES. The formulas given in Articles 312.4 - 312.5 may also be used for comparison of the annual cost of two or more routes. One common alternative is that of a road with good alignment and truck travel speed but more costly construction than an alter- nate road with poorer alignment and slower travel speed. Another common alternative is that of a longer route on a gentle favorable grade, as around the point of a ridge, versus a shorter route Involving an adverse grade and a steeper favorable grade, as over the ridge. Example ; 1. Longer route segment 3.67 miles of 3 percent favorable grade. Trucking cost 56.2 cents per M board feet. Construction cost $55,050 at 6 percent amortization plus interest = $3,303. Annual maintenance at $300 per mile = $1,101. Total annual cost $4,404. 2. Shorter route segment 2.0 miles at 8 percent favorable, 1 mile at 5 percent adverse. Trucking cost 81 cents per M board feet. Construction cost $41,000 at 6 percent = $2,460. Maintenance at $400 per mile (steeper grades, sharper curves). Total $3,660. Then the annual volume of haul "V" at which the two routes will be equal in cost is: V = = 3,000 M board feet .81 - .562 .248 Thus, the longer route will be the more economical if the annual volume hauled exceeds 3 million board feet. 64 330 CONSIDERATIONS IN ROAD LOCATION 331 TRUCK PERFORMANCE 331.1 TRUCK TRAVEL TIME. The forest road engineer is con- stantly faced with making decisions as to what degree of curve to locate. He is prone to decide on the basis of what he sees before him--the grade line and the topography--and what he can visual ize--the road prism and the earthwork. In his concentration he is apt to forget to consider the effect of his decision on the vehicle which will travel the road. When making a decision on gradient or curvature he should ask himself, *’What effect will my decision have on truck travel time?" To help the forest road engineer to achieve the best balance between gradient and curvature. Tables 331-1 to 331-6 are given. They were derived from formulas and graphs in the 1956 edition of reference(^Z). Table 331-1, "Effect of Gradient on Truck Spped," gives the loaded, empty and average round trip speed in miles per hour and travel time in minutes per round trip mile on favorable and adverse grades for a vehicle of 150 H.P. and 70,000 lb. G.C.W. (Gross Combination Weight of loaded log truck and trailer). Table 331-2 gives the same data for 200 H.P. trucks. Note that the speeds for gradient are on tangents not af- fected by curves. •'Minutes per round trip mile" is the sum of the travel times of the loaded and empty truck on a one mile segment of road. Table 331-3, "Effect of Curvature on Truck Speed" gives the speed in M.P.H. and the round trip travel time on blind curves on one-lane roads from 3 to 70 degrees of curvature. The same data is given for open curves on one-lane roads and for all curves on two-lane roads from 8.6 to 70 degrees. Note that these speeds are on curves not affected by gra- dient. A top speed of 40 M.P.H. on gravel-surfaced roads is assumed. Table 331-4, "Truck Speed Controlled by Curvature," gives for one-lane roads and 10, 15, 20 and 25 curves per mile the average round trip M.P.H. and minutes per mile for average degrees of curvature from 5 to 70 degrees. In using this table average only the curves of degrees greater than one-fourth the largest degree of curve (sharpest curve) in the mile. For example, if the sharpest curve is 60 degrees, average only curves of more than 15 degrees. Table 331-5 fives the "Gradient on Which Round Trip Speed Equals Speed on Curves," for blind curves from 3 to 75 degrees and open curves from 5 to 75 degrees for 150 H.P. 70,000 lb. G.C.W. vehicles. Table 331-6 gives similar data for 200 H.P. 70,000 lb. G.C.W. vehicles. The road locator should also note the practical points mentioned in Article 322.7 with regard to slackening gradient for gear shifting. To avoid gear shifting on curves on adverse grades, to overcome curve re- sistance, reduction in gradient of 0.04 percent per degree of curve is recommended. For example, reduce the gradient on a 25 degree curve by (25 X 0.04) or 1 percent, on a 50 degree curve by 2 percent, on a 75 degree curve by 3 percent. 65 o EFFECT OF GRADIENT ON TRUCK SPEED Gravel Surface TABLE 331-1 TABLE 331-2 150 HP 70, 000 lb. G.C.W. 200 HP 70,000 lb. G.C.W. Per Round Per Round Trip Mile Trip Mile Grade Loaded Empty Average Min- Grade Loaded Empty Average Min- 7. MPH MPH MPH utes % MPH MPH MPH utes Adverse Down Adverse Down 10 4.8 18.5 7.6 15.75 10 6.3 18.5 9.4 12.70 8 5.8 21.8 9.2 13.10 8 7.6 21.8 10.7 10.60 6 7.3 26.7 11.5 10.50 6 9.4 26.7 13.9 8.60 4 9.8 34.3 15.2 7.90 4 12.9 34.3 18.7 6.40 3 11.7 40.0 18.1 6.60 3 15.6 40. 0 22.5 5.35 2 14.5 40.0 21.3 5.60 2 19.0 40.0 25.7 4.65 1 19.0 40.0 25.8 4.65 1 24.4 40.0 30.0 3.95 0 27.9 40.0 32.9 3.b5 0 33.3 40.0 36.3 3.30 Favorable Favorable 1 33.3 40.0 36.3 3.30 1 40.0 40.0 40.0 3.00 2 40.0 37.5 38.7 3.10 2 40.0 40.0 40.0 3.00 3 40.0 33.0 36.2 3.30 3 40.0 40.0 40.0 3.00 4 34.3 28.6 31.2 3.85 4 34.3 40.0 36.8 3.25 6 26.7 22.6 24.5 4.90 6 26.7 40.0 32.1 3.75 8 21.8 18.5 20.0 6.00 8 21.8 34.2 26.6 4.50 10 18.5 15.6 16.9 7.10 10 18.5 30.0 22.9 5.25 12 16.0 13.5 14.6 8.20 12 16.0 26.4 20.0 6.00 14 14.1 11.8 12.8 9.30 14 14.1 23.0 17.6 6. 80v 16 12.3 10.5 11.3 10.60 16 12.3 20.7 15.4 7.80 18 10.6 9.6 10.0 12.00 18 10.6 18.7 13.5 8.90 TABLE 331-3 - EFFECT OF CURVATURE ON TRUCK SPEED Safe Speed on 1-Lane Blind Curve Road Safe Speed on Open Road - All Curves Curve 1-Lane 2-Lane Road Degree Per Round Trip Mile Degree Per Round Trio Mile Curve Speed Minutes Curve Speed Minutes 0.0 40.0 3.0 8.6 40.0 3.0 3.0 34.0 3.5 10.0 37.0 3.2 5.0 28.6 4.2 15.0 28.3 4.2 10.0 22.2 5.4 20.0 26.2 4.6 15.0 18.7 6.4 25.0 23.4 5.2 20.0 16.0 7.5 30.0 21.4 5.6 25.0 14-.7 8.2 40.0 18.4 6.5 30.0 13.8 8.7 50.0 16.4 7.2 40.0 12.1 9.9 60.0 15.1 7.9 50.0 11.5 10.5 70.0 14.0 8.6 60.0 10.8 11.1 70.0 10.2 11.7 66 TABLE 331-4 TRUCK SPEED CONTROLLED BY CURVATURE Average 10 Curves 15 Curves 20 Curves 25 Curves Degree Per Mile Per Mile Per Mile Per Mile Curve Ave . Min- Ave. Min-r-.' Ave. Min- Ave. Min- MPH utes MPH utes MPH utes MPH utes 5 32.0 3.7 30.8 3.9 30.5 3.9 30.1 4.0 10 23.8 5.0 22.4 5.3 22.0 5.4 21.6 5.6 15 19.9 6.0 18.5 6.5 17.8 6.7 17.3 6.9 20 19.1 6.3 17.7 6.8 16.9 7.1 16.4 7.3 25 18.1 6.6 16.4 7.3 15.6 7.7 15.0 8.0 30 17.1 7.0 15.4 7.8 14.5 8.3 13.9 8.7 40 15.9 7.5 14.0 8.5 13.0 9.2 12.6 9.5 50 15.2 7.9 13.4 9.0 12.3 9.8 11.5 10.5 60 14.7 8.2 12.7 9.4 11.7 10.3 10.9 11.0 70 14.3 8.4 12.5 9.6 11.2 10.7 10.3 11.6 TABLE 331-5 GRADIENT ON WHICH ROUND TRIP SPEED EQUALS SPEED ON CURVE 150 HP 70,000 lb. G.C.W. Bl ind Curve Degree Favorable Grade % Adverse Grade o/ /o Open Curve Degree Favorable Grade % Adverse Grade “V /«» 3 3.25 5 4.70 0.60 5 1.30 10 6.95 1.80 10 2.45 15 8.70 2.80 15 4.80 0.65 20 10.80 3.70 20 5.45 0.95 25 12.00 4.20 25 6.45 1.55 30 12.95 4.70 30 7.30 2.00 35 14.00 5.20 35 8.10 2.50 40 15.00 5.65 40 8.95 2.90 45 15.40 5.90 45 9.60 3.20 50 15.80 6.10 50 10.25 3.50 55 16.40 6.40 55 10.90 3.80 60 17.00 6.60 60 11.60 4.00 65 17.40 6.80 65 12.20 4.30 70 17.80 7.00 70 12.70 4.60 75 18.20 7.20 75 13.20 4.90 67 TABLE 331-6 9 GRADIENT ON WHICH ROUND TRIP SPEED EQUALS SPEED ON CURVE 200 HP 70,000 lb. G.C.W. B1 Ind Favorable Adverse Open Favorable Adverse Curve Grade Grade Curve Grade Grade Degree % 7, Degree 7o % 3 5.7 0.6 5 7.1 1.3 5 10 10.5 3.1 10 3.9 15 13.0 4.0 15 7.2 1.4 20 15.5 5.1 20 8.3 2.0 25 16.8 5.7 25 9.7 2.7 30 17.6 6.1 30 11.0 3.4 35 18.6 6.5 35 12.1 3.7 40 19.7 6.9 40 13.3 4.1 45 7.2 45 14.1 4.4 50 7.5 50 14.9 4.8 55 8.0 55 15.6 5.1 60 8.4 60 16.4 5.5 65 8.6 65 16.9 5.7 70 8.8 70 17.5 6.0 75 9.0 75 17.8 6.2 331 • 2 LOG TRUCKING COST. Log trucking costs for economic analy- sis of roads may readily be obtained by applying the current machine rate to the "minutes per round trip mile," for the relevant conditions, in Tables 331-1 to 331-6. The applicable machine rate is the current cost of owning and operating a log truck and trailer for one minute, excluding tire cost. Tire cost is computed on a mileage basis. The machine rate is com- posed of the following cost elements: Current operating cost, including labor, fuel, lubricants, main- tenance and repairs. Ownership cost. Including depreciation. Interest, taxes and in- surance. Then '•minutes per round trip mile" multiplied by machine rate per minute, plus tire cost for two miles, gives hauling cost in dollars per mile of haul. This cost divided by the average log load gives the unit cost in cents per M board feet per haul mile. Example: Given 15 curves per mile, average curve 30 degrees, per- cent favorable grade. In Table 331-1 read 7.1 minutes per round trip mile for 10 percent grade. In Table 331-4 read 7.8 minutes per round trip mile for 15 curves per mile averaging 30 degrees. Therefore, travel time is con- trolled by curvature. If current machine rate for 150 HP log truck and trailer is 20 cents per minute, and tire cost is 20 cents per mile, or 4C 9 68 cents per round trip mile, then cost per mile haul = 7.8 minutes X $0.20 per minute = $1.56 plus $0.40 tire cost = $1.96 per mile. If average load is 6 M board feet, then $1.96 divided by 6 = 32.7 cents per M board feet per haul mile. 331.3 MOMENTUM GRADES. The use of "momentum" or "veloc- ity" adverse grades offer opportunity to decrease curvature or length of road with consequent savings in construction cost and travel time. The momentum of the vehicle at the bottom of the grade is utilized to help overcome grade resistance. The approach to the momentum grade and the grade itself should be on a tangent so that speed is not restricted by curvature. Momentum grades are adapted to ridge-crest routes and to crossing draws on tangent to avoid curving into and out of the draw on a grade contour, thus eliminating three curves. Following is a formula for computing the length of a momentum grade: Distance = Initial Momentum - Final Momentum (Grade + Rolling Resistance) (GCW)-(Net Tractive Effort) Net Tractive Effort = lorpue x Total Gear Reduction x .72 Tire rolling radius in feet For example, given a 200 HP, 70,000 lb. GCW truck, 584 ft. lb. torque at 1800 RPM, tire rolling radius 1.6 ft. Total Gear Reduction in direct drive 8.1. Rolling resistance, compacted gravel, equivalent to 1.8 percent grade. Net Tractive Effort = 584 X 8 X .72 ^ 2100 lbs. 1.6 Assume that an 8 percent momentum (adverse) grade is approached by a 6 percent favorable grade on which the speed will be 26.7 MPII or 39.2 feet per second. What distance will the truck travel up the 8 percent grade in direct drive before the speed slows to the speed on an 87. adverse grade of 7.6 MPH or 11.1 feet per second? (Grade + Rolling Resistance) (GCW) = (.08 + .018) (70000) = 6860 lbs. Momentum = (GCW) (Velocity ft. per sec. ^) 64.4 Initial Momentum = (70,000)(39.2^) = 1,670,210 ft. lb. 64.4 Final Momentum = (70,000)(11.1 ) = 133,920 ft. lb. 64.4 Distance = l.o70«210 = 133,920 = 1,536,290 = 323 feet 6860 = 2100 4760 Thus any distance less than 323 feet on the 8 percent momentum grade can be made in direct drive without shifting gears. The difference in eleva- tion is 323 X .08 or 25.8 feet. Any momentum grade with a difference in elevation of 25.8 feet would have the same effect. For example on a 69 10 percent grade the momentum distance would be 258 feet; on a 6 percent grade 430 feet. If a shift were made to a lower gear with greater gear reduction and net tractive effort a longer momentum grade could be used. In the above example the distance the truck would coast up without power until the speed dropped to 7.6 MPH would be; 1 , 536,290 or 224 feet. 6,860 332 CONSTRUCTION METHODS 332.1 CONSTRUCTION MACHINERY AVAILABLE. The construction method which will be used Is an Important economic consideration In road location. A timber sale road to be built by a logging operator, whose only grading equipment Is a bulldozer, requires different design than an access road to be built by a contractor equipped with scrapers and power shovels as well as bulldozers. Table 332-1 gives a comparison of produc- tion and costs of excavation and haul. Economy in grading with the bulldozer will be achieved If the road Is so designed that: 1. Earth is side cast and wasted rather than end hauled. 2. End hauls are kept short. (Table 332-2) 3. Earth is moved down-grade with the aid of gravity, not up. 4. Fill material is borrowed rather than hauled farther than economic limit of bulldozer haul. 5. Cuts In rock requiring blasting before bulldozing are mini- mized. 6. Soft or swampy ground and blue clay is avoided. The advantages of balanced sections In reducing soil disturbance and exposure to erosion should be weighed against the increased cost of grading balanced sections of excavation and embankment with a bulldozer. In designing for power shovel excavation; 1. Rock cuts can be heavier in rock which the power shovel can excavate without blasting. 2. Long end hauls are economical with power shovel and dump trucks. 3. Therefore, balanced sections can be used. 4. The power shovel can work on mats in soft or swampy ground where a bulldozer could not operate. In designing for scraper grading: 70 1. Balanced sections are economical. 2. End hauls up to 1,000 feet can be planned. This is the customary free haul distance in road construction contracts. 3. Rock and swamp is to be avoided. TABLE 332-1 COMPARATIVE PRODUCTION AND COSTS PER HOUR CLAY SOIL, BANK CUBIC YARDS, 50 MINUTE HOUR Haul Bulldozer (185 HP) Scraper (7- 9 Cu. Yd. ) Feet Output Cents per Output Cents per Cu. Yd. Cu. Yd. Cu. Yd. Cu. Yd. 50 240 5.6 100 130 10.3 150 100 13.4 200 75 17. » 250 60 22.3 300 50 26.8 350 40 33.5 112 12.4 400 30 44.8 107 13.1 600 90 15.5 800 78 17.9 1000 68 20.6 POWER SHOVEL Size Output in Cu. Yd. Cents per Cu. Yd. Cu. Yd. Digging Digging Easy Medium Hard Easy Medium Hard 3/4 125 84 60 9.2 13.7 19.2 1 168 112 80 8.9 13.3 18.6 U 238 160 110 8.3 12.3 17.9 Dump truck haul, 30 cents per cu. yd. first mile. TABLE 332-2 BULLDOZER EARTH MOVING PRODUCTION IN PERCENTAGE OF PRODUCTION ON 10% FAVORABLE GRADE FOR 100 FT. HAUL Horizontal lines indicate approximate economic limit ot haul for various grades. Haul Adverse Grade % Level Favorable Grade % Feet 10 5 0 5 10 15 20 50 54 72 90 126 161 198 234 75 43 100 "33 44 56 76 100 122 144 125 47 150 38 54 70 86 102 200 42 54 65 77 250 33 1 43 52 62 300 35 43 51 350 36 43 71 332.2 CONSTRUCTION COST FACTORS. The construction cost factor over which the road engineer exercises the most control, through location and design, is earthwork yardage. Any increase in depth of cut or height of fill at center line increases the yardage of earthwork and the clearing and grubbing acreage, with consequent increase in costs. Culvert length Increases with Increase in fill height. In fitting a grade line to a pro- file at a class III road, Calders’ Table 18 is a useful guide to the effect on yardage of raising or lowering the grade line. (4/) Actual yardage will be greater, since Calders' Table 18 is for a half-base in excavation of 11 feet, whereas the corresponding half-base of a class III road is 10 feet plus (3 X surfacing depth in feet). Calders' Table 17 is helpful in find- ing the cut on steep side slopes to obtain the desired width of subgrade on solid ground. Where surfacing rock is scarce and surfacing costs high, saving in length of road, even at an increase in earthwork, is desirable. Whether rock can be ripped is an important cost factor. Rock which can be ripped with a tractor-drawn ripper can be excavated at much lower cost than rock which requires blasting. The use of the Reflecting Seismograph makes it possible to determine whether rock is rlppable, as well as measuring the thickness of the overburden and the thickness of rock layers of differing densities down to the top of the hardest layer. The instrument is also useful for finding depth to bed rock for bridge pier foundations. The development of tractors of 335 horsepower has greatly extended the range of rippable rock. (8/) 332.3 ECONOMIC KAXIMUll DEGREE OF CURVE. The road engineer is frequently faced with making a decision on the degree of curve to locate around sharp ridges where a large central angle is involved. Table 332-1 gives factors for determining the maximum degree of curve, based on sav- ings in trucking cost compensating for increase in construction cost, for various side slopes. The central angle divided by the factor equals the degree of curve. Side slope percent is measured at the mid-point. Fac- tors are given under column headings at million board feet per annum to be hauled the first line being for a blind curve and the second line for an open curve. The table is derived from a study by Nelson. (^Z) Excavation yardages are based on common up to 35 percent side slope 50 percent rock on 50 percent side slope, and 100 percent rock on 70 percent and steeper side slopes. Unit costs are 40 cents per cubic yard for common and $1.20 per cubic yard for rock. Annual amortization rate is 4.5 percent: truck machine rate is 46.8 cents per minute for a 6 M board feet payload. Since the annual haul required to pay for con- struction is equal to amortized construction cost divided by the saving in hauling cost, annual volume for any other unit costs is proportional. For example, its excavation rates are 20 and 60 cents per cubic yard, or one-half the rates used in compiling the table, trucking rate unchanged, annual volume tor a given factor will be one-half the volume shown in the column heading. 72 TABLE 332-2 FACTORS FOR DETERMINING DEGREE OF CURVE BASED ON SAVINGS IN TRUCKING COST COMPENSATING FOR INCREASE IN CONSTRUCTION COST Blind Curve: Open Curve: Mill ion 1 1.5 Board 2 3 Feet per 3 4.5 Annum 5 7.5 10 15 20 30 30 45 Side Slope 7. 10 2.42 3.10 4.16 5.00 6.67 5.94 20 1.65 2.14 2.94 3.58 4.63 5.94 30 1.21 1.61 2.16 2.65 3.49 4.51 5.33 40 0.89 1.21 1.60 2.03 2.73 3.52 4.17 50 0.70 0.96 1.23 1.60 2.20 2.84 3.51 60 0.57 0.79 1.00 1.31 1.83 2.41 2.87 70 0.45 0.64 0.84 1.10 1.54 2.10 2.55 80 0.39 0.54 0.71 0.93 1.33 1.89 2.29 90 0.35 0.46 0.63 0.81 1.17 1.73 2.09 100 0.33 0.41 0.60 0.73 1.04 1.64 1.93 Degree of Curve = Central Angle factor Example: If side slope Is 50 percent, annual haul 5 million bd. ft., for a blind curve, the factor is 1.60, If the central angle I is 90° then the maximum degree of curve = 90 / 1,60 = 56°. For an open curve interpolating in the table, f = 1.29 and degree of curve = 90 / 1.29 = 70°. 333 SOIL AI3D NATER RESOURCE PROTECTION 333.1 DRAINAGE AND EROSION CONTROL. As provisions for drain- age and erosion control are carried out during design and construction, they are covered in detail under divisions 700 ’’Road Design” and 800 ’’Construction Engineering.” However, they are mentioned here as a remin- der that much can be done to minimize drainage and erosion problems in the location of the road. The location which results in the least soil disturbance, with the lightest cuts and fills, is the best location from the standpoint of erosion control, as well as grading cost. Breaks in long sustained grades, to permit ditch water to be carried by a cross drain to the lower side of the road, will help drainage as well as truck performance. Streams and draws should be crossed at the best sites for culverts. Switchbacks and their approaches create drainage problems as well as trucking problems. Avoiding slide, slump, sheet erosion, poorly drained, and other such problem areas in location will avoid construction and maintenance problems, and erosion due to them. Locating a road on the lowest possible gradients will reduce maintenance cost as well as trucking cost. The erosive effect of water increases with Increase in gradient. Road surfacing wear from tire action depends upon truck speed. The relation between road gradient and water action, tire action and the two combined is shown in the following tables by Nelson. (^/) Data are expressed as the ratio to action on a 6 percent grade. 73 Road Water Tire Combined Grade Action Action Action Percent Ratio Ratio Ratio 0 0.06 2.26 1.00 2 0.13 2.26 1.04 4 0.45 1.61 0.95 6 1.00 1.00 1.00 8 1.91 0.67 1.38 10 3.20 0.48 2.03 12 4.92 0.36 3.05 14 7.09 0.28 4.16 16 9.65 0.22 5.59 18 17.73 0.18 7.33 333.2 recreational considerations. Locating a road tnrough potential recreation areas requires special consideration of the protec- tion ot recreational values* These include camp sites, fishing streams, and scenery. The safety of the traveling public is also a consideration. Since the sight of logging slash or slash burns is objectionable to re- creationists, screening is desirable. In locating a road through a re- creational area the following measures are recommended; 1. Locate the road well back from the main stream to avoid Interference with the stream channel or siltation of the water. 2. Preserve camp ground sites by following the contour around the foot of the slope, instead of crossing the flat. 3. Provide ample turnouts and access to parking spaces. 4. Leave a fringe of timber between the road and the stream, if this can be done without creating a windthrow hazard. Provide for felling all danger trees. 5. Locate landings on spurs off of the main road. A spur to a landing should leave the main road on a curve, so the traveling public cannot see the logging slash. 6. Leave a scenic belt of timber between the road and the clear-cut setting boundary. 7. Minimize cuts and fills and resulting scars. 8. Locate gravel pits and borrow pits out of sight of the road so far as possible. 9. On a ridge crest or hillside road which will be used by the public, flatten the gradient at scenic vista points and provide ample turnout and parking apace. 7A The relative weight to be given to recreational considerations as opposed to economic and other considerations is a matter of admin- istrative policy decision. BIBLIOGRAPHY 1. Region 6 Forest Road Standards, Surveys and Plans, Division of Engi- neering, U. S. Forest Service, Portland, 1958 2. Byrne, J. J., Nelson, R. J., Googins, P. H. ,”Cost of Hauling Logs by Motor Truck and Trailer." Pacific Northwest Forest and Range Experi- mental Station, May 1956. New edition revised by Walters, William T. , to be published by U. S. Government Printing Office, Washington, D. C., 1960 3. Stenzel, George, "The Natural Resource Road Program of the Pacific Logging Congress." The Pacific Logging Congress, 616 American Bank Building, Portland, Oregon, 1958 gratis 4. Calders* Forest Road Engineering Tables, Calder, Lester S, and Douglas G. , 1828 Ililyard Street, Eugene, Oregon 5. Nelson, Roger J. , "Al ignment of Logging Roads" U. S. Forest Service Region 6 mimeo 1955 6. Nelson, Roger J., "Effect of Gradient on Surface Replacement " dittoed 1956 7. Pearce, J. Kenneth. ’’Economic Log Truck Sizes," Loggers’ Handbook, Volume XVII, Pacific Logging Congress, Portland, Oregon, 1957 8. Cat D-9 No. 9 Ripper Performance Chart, Caterpillar Tractor Company, Peoria, Illinois, November 1959 9. Instruction Manual. Refraction Seismograph Model MD. Geophysical Specialties Company, 4206 Longfellow Avenue, Minneapolis, Minnesota, 1959 75 CONTENTS Page 400 ROUTE PROJECTION AND RECONNAISSANCE 78 410 ROUTE PROJECTION 411 Route Projection On Large Scale Maps 78 .1 Introduction, .2 Selecting control points, .3 Plotting grade contour, .4 Plan projection, .5 Trial profile, .6 Cost comparison of alternate routes, .7 Final check. 412 Route Projection On Aerial Photos 81 .1 Introduction, .2 Determining differ- ences in elevation by parallax measurement, .3 Correction of paral- lax measurements for photo distortion, .4 Distance between points by radial line plot, .5 Plotting grade line on photos, .6 Meas- uring elevation differences by templet method, .7 Bureau of Public Roads method of photogrammetr ic route projection, .8 Slope measure- ment for cost comparison. 420 FIELD RECONNAISSANCE 99 421 Introduction 99 .1 Definition, .2 Objective of the recon- naissance, .3 Importance of the reconnaissance, .4 Seasons for reconnaissance. 422 Reconnaissance For Unprojected Route 100 .1 Extensive reconnaissance, .2 Jeep roads. 423 Reconnaissance for Projected Route 101 .1 Field check, .2 Intensive reconnais- sance, .3 Running grade line, .4 Running grade line for curves, .5 Grade separation and vertical curves BIBLIOGRAPHY 108 FIGURE 411-1 Plan of Projected Roads 82 FIGURE 411-2 Profile of Projected Road, Class 111 83 FIGURE 411-3 Curve Templet 84 76 FIGURE 412-1 Difference In Elevation by Parallax Measurement Theory 85 FIGURE 412-2 Radial Line Plot 90 FIGURE 412-3 Elevation Difference by Templet Method 93 FIGURE 423-1 Plan and Profile 105 FIGURE 423-2 Grade Separation 107 FIGURE 423-3 Landing Profile 107 77 400 ROUTE PROJECTION AND RECONNAISSANCE 410 ROUTE PROJECTION 411 ROUTE PROJECTION ON LARGE SCALE MAPS 411.1 INTRODUCTION. "Route projection” is the laying out of a route for a road on a topographic map or aerial photo. The route de- fines the narrow strip of land within which the field preliminary sur- vey is made. "Large scale maps” are the 400 feet to the inch, 20 feet contour interval maps made by the Cartographic Section, Oregon State Office, Bureau of Land Management, or maps made by the method given in Chapter 220. Route projection on small scale maps, such as enlarge- ments of U.S.G.S. quadrangles, is similar but less detailed. Prior to starting the route projection, ascertain the proposed standard of the road. Assemble other pertinent basic data listed in Section 211, any logging plans which have been made, and soil or geo- logical maps of the area served by the road. For economic analysis, collect data on timber volumes, annual cut, and road construction and log trucking costs. Obtain the aerial photos covering the routes for study for tone indications of granular soil and poorly-drained ground. Review of Chapter 320 "Considerations in Route Selection," and Chapter 330 "Considerations in Road Location” before starting the route projection is recommended. The consecutive steps to follow in making a route projection are given in ensuing Articles 411.2 to 411.5. This procedure is also followed in paper location on strip topography (Section 522). 411.2 SELECTING CONTROL POINTS. 1. Determine the terminal control points: where to begin from an existing road or location survey, and where to end the present project. If the road may be extended in the future, the upper terminal should be at a point suitable for contin- uing the road. This may necessitate projecting the road beyond the present project, to insure that it does not "dead end.” The lower terminal is usually the more flex- ible, and subject to change when Intermediate control points are found, and the grade contour projected. 2. Look for major control points between the terminals. Pos- sible control points are listed in Article 322.5. These are usually saddles or passes, benches for spur road junc- tions, and suitable crossings of large streams, where bridges or large plate culverts are required. If a log- ging plan is involved, landings along the road route may be control points. If projecting a main road from which stub spurs to landings will take off, suitable junction points for the spurs are controls. Work from the top down, as the valleys and control points tend to constrict at the higher elevations and to widen out at the lower elevations. 78 c 3. Look for minor control points along the probable route be- tween major control points. These include points at which obstacles can be passed, such as above or below cliffs, rock outcrop or slides, and either side of the swamps. Mark these points with a red pencil for "danger”. Look for evi- dence of soft or poorly drained ground, and the best places to cross or avoid them, and for the best crossings of side streams. Mark these with blue pencil for "water". 4. Where the route will follow a water grade along a main creek, study both sides of the valley to determine whether to pro- ject alternate routes paralleling the creek on each side of the valley, or, in the case of a meandering stream or a val- ley with cliffs or steep side slopes alternating from one side to the other, to project a route which would cross the creek at Intervals. It may be necessary to project all three alternate routes and compare costs to determine the preferable route. 411.3 PLOTTING GRADE CONTOUR. 1. The next step is to plot a grade contour between control points. A grade contour is the line which follows the ground surface at the uniform grade between two control points. The grade contour is drawn as a guide to the pro- jected route. Measure the approximate distance between control points. If the line is not reasonably straight, step off the distance with dividers or measure with a Hamilton map measurer. Interpolate the control point ele- vations, and compute the grade between them. Set dividers- at the distance for one contour Interval at this grade. Example: Difference in elevation between control points 160 feet. Distance 2,000 feet, grade 8%. Set dividers at 20/. 08 = 250 feet for 20 feet contour interval. Starting at one control point, step off successive contours with the dividers. If the trial grade contour does not hit the elevation of the other control point, recompute distance and grade, re-set dividers and step off a second trial line. 2. When the required grade has been found, set pencil draw- ing compass at the correct distance for one contour inter- val. Step off the grade contour line, ticking each con- tour crossed on the map with the pencil point. In going around sharp ridges or narrow valleys, take care not to exceed the maximum degree of curve for the standard of road. Make a plastic curve templet with a radius at map scale equal to the radius of the maximum curve. Lay it on the map and step off around it with the compass. Keep track of the distance and compute the contour which the grade will hit at the estimated end of the curve. If the topography is broken, or the grade percent low, it is 79 preferable to set the compass at one-half the grade dis- tance for one contour interval and mark every other tick half-way between the contour lines. 411.4 PLAl^ PROJECTION. Draw a plan of the road following the grade contour as a guide. In plan view a road consists of a series of straight lines, "tangents,” connected by curves. The curves are geomet- rically tangent to the straight lines, the radii being perpendicular at the beginning and ends of the curves. With a transparent drafting tri- angle, draw a series of tangents through two or more tick marks which are in line. Fit curves to the tangents by trial. Curve fitting is facilitated by using a transparent plastic curve templet with curves at 5° or 10° intervals, to the scale of the map. Recommended templet design is shown in Figure 411-3. 411.5 TRIAL PROFILE. A profile is desirable as a check on the gradients as well as to indicate where heavy earthwork is involved, for use in construction cost estimating and locating culverts. Set the dividers at a convenient distance to map scale, as one-half inch or two stations for 400 feet to the inch scale, and step off along the projec- tion line. Read off and tabulate the station and elevation at each divider point. Elevations can be easily Interpolated to k contour, or 5 feet on the 200 foot contour interval map. Number every 5th divider point, or every 10 stations. Plot the profile on profile paper. A con- venient scale is 1 inch = 400 feet horizontal scale and 1 inch = 40 feet vertical scale. Plot the grade line on the profile. If the grade between any two control points exceeds the allow- able maximum, due to the projection line being shorter than the grade contour, revise the projection to increase the length, if possible. Plot a trial profile of the revision, and check the grade line. If it is not possible to develop sufficient length of road to keep within the maximum grade limit, then new control points and a new route must be found. Plot the trial profile for the most critical segments first. This may obviate waste of time in plotting other sections which have to be abandoned if the critical section proves to be unusable. 411.6 COST COMPARISON OF ALTERNATE ROUTES. If alternate routes are projected, a comparative cost estimate is made to determine the most economical route. 1. Construction cost estimate. Divide the road plan into sec- tions of uniform side slopes to the nearest 10 percent. Scale the distance between contours adjacent to the pro- jection line at sample points and divide into the differ- ence in elevation to obtain slope percent. Estimate clear- ing and grubbing and grading costs. Figures 5 and 6, ref erence(^/5, Division 300 are useful for estimating quan- tities. Estimate the culverts needed and culvert costs. If sections of heavy grading are Involved, such as deep cuts through ridges, or high fills, a rough estimate of the earthwork can be made by reading off cuts or fills from the trial profile, scaling side slopes, and 80 obtaining cubic yards per 50 feet from Calders* Tables 18 or 19. For cuts exceeding 13 feet or fills exceeding 5 feet, the limit of the tables, sketch cross sections and compute volumes. The costs of temporary bridges may be estimated from local experience. Cost estimates on permanent bridges should be obtained from the state office, since they will usually be designed by Bureau of Public Roads bridge engineers. The relative availability of surfacing rock may be an important cost consideration. 2. Transportation cost estimate. Comparative truck travel tires may be found from the tables given in Section 331. Log trucking costs may be computed by using cost data in reference(^Z) Division 300. 3. Maintenance cost estimate. No comparison of alternate routes is complete without considering maintenance costs. A road which is cheaper in initial construction cost may be the more costly over a period of years, when mainten- ance is Included. As maintenance costs vary with surfac- ing material and traffic, as well as gradient and curva- ture, local experience is the best guide to maintenance cost estimating. 4. A comparison of the totals of construction, maintenance, and trucking costs weighted by the volume of timber to be hauled over the road will indicate the economlpal route. Other factors such as recreational use may deter- mine the preferable route. 411.7 FINAL CHECK. Transfer the projected route to the road key map or overall transportation plan map. Note whether the route fits in with the overall road system for the area. All work on maps and photos should be cross-referenced with field notebooks of reconnais- sance and survey. All field books should be indexed as the work pro- gresses. 412 ROUTE PROJECTION ON AERIAL PHOTOS 412.1 INTRODUCTION. In the open pine forests, road routes may be satisfactorily projected on aerial photos. In dense Douglas-fir forests, routes cannot be projected in as much detail. However, photo- projection may eliminate unfeasible routes and reduce the time spent in field reconnaissance. The consecutive steps in route projection are similar to those given in Section 411. Visible control points are located. The differ- ence in elevation between each two control points are determined. The horizontal distances between the control points are measured. The aver- age gradients between control points are computed. In dense forest cover, some control points may not be visible, and must be found by reconnais- sance in the field. Control points which are usually visible on aerial photos are the terminals, saddles, benches, and crossings of the larger 81 Q r r 00 FIG. 411-3 DIAGRAM FOR CURVE TEMPLET SCALE I INCH = 100 FEET 84 FIGURE 412-1 DIFFERENCE IN ELEVATION BY PARALLAX MEASUREMENT THEORY I 85 9 streams in the open. Crossings of smaller streams are often obscured by the trees. Rock outcrops and slides may be visible or hidden. Where forest cover obscures the ground, it is necessary to know the a average height of the trees in order to obtain ground elevations. The experienced photo-interpreter can detect swamps and poorly-drained soils which should be avoided. Gravel deposits suitable for embankment or surfacing may be detected by their light color tone and well-drained appearance. When verified on the ground, mark them with the symbol ^ on photo and map. Since most foresters have had a course in forest photo-inter- pretation, but not in photogrammetry , methods of determining differences in elevation are given in detail in ensuing articles. To make parallax measurements requires skill, but skill can be acquired with practice. The methods given in Articles 412.2 and 412.3 were developed by Profes- sor Hiram Chittenden at the University of Washington and are used by students. 412.2 DETERMINING DIFFERENCES IN ELEVATION BY PARALLAX MEASUREMENT. 1. Preparation of stereo pair of photos. a. With a drop pen mark the principal points, PPj and PP2 on the centers ot the photos, 1 and 2 at the intersection ot lines connecting the fiducial marks on the edges ot the photos. b. Mark the conjugate points CP2 on photo 1 and CPj^ on photo 2. (Figure 412-1) c. Mark the flight line connecting the principal point and the conjugate point on each of the photos. d. If the elevations of any points on the photos are known, or any distances between two points, as along existing roads or between pin-pointed section or quarter corners, mark them on the photos or on a transparent overlay. Note any tree heights for which data are available. e. Tape down the photos under a mirror stereoscope so that the flight lines and the principal and conjugate points coincide precisely. 2. Photo-measurements required. The following measurements (Figure 412-1), are made made with either a parallax bar to 0.01 MM or a 50 or 60 engineers scale. One-half divi- sion on the 50 scale = 0.01 inch. a. Separation distance "D" between principal points PP, and PP2 86 b. Distance "Da", measured parallel to the flight line between the images of one of the two control points, the elevation of which is known or assumed. c. Distance"Db", measured parallel to the flight line between the images of the other of the two control points. Control points "A” and "b” must appear in the common overlap of the stereo pair. 3. Computation of flight altitude. To compute difference in elevation between two points by the parallax measure- ment method, "H*’, the flight altitude above datum (usu- ally sea level) and "ha" the elevation above datum of point "a", are required. Flight altitude may be calcu- lated from a known distance and elevations on the photos. The terminal photos of each flight made for the Bureau of Land Management show the average scale R.F. for the flight and the focal length "f" of the lens. Flight height above the ground = flight altitude - ground elevation = (H-h), then R.F. = f (H-h) The Bureau of Land Management photos are usually 1 : 12,000 scale taken with 12 inch lens, or 1 ; 15,840 scale taken with 8^ inch lens. The latter scale is preferable for road projection due to greater relief displacement. Then aver- age flight height is 1 = 0.6875* (H-h) = 10,890 15840 (H-h) Flight altitude H = (H-h) + h. If the average ground ele- vation was, say, 500 ft., it would be 10,890 + 500 = 11,390 ft. Since the photo scale varies with the elevation, it is desir- able to calculate H for the stereo-pair of photos from a known distance and elevation. R.F. = Photo distance ground distance Average elevation h = hj + hjj 2 (H-h) = f R.F. Example; Distance between A and b 1762 feet or 21,144 inches. Photo distance a to b = 1.524 inch. Elevations; hg 395, hb 536 average 465 feet. f = 8^ inches = 0.6875 feet . R.F. = 1.524 = 1 21,144 13,870 (H-h) = f_ = (0.6875) (13870) 9535 ft. R.F. 87 H = 9535 + A65 = 10,000 ft. 9 *4. Computation of difference In elevation. The parallax equation for dh, the difference In elevation between two points "a” and ”b” (H-h^) (Da - D^) D-D, dh = A positive value for (Dg - D^) Indicates a rise In ele- vation; a negative value, a drop In elevation. Example; Given H = 10,000 feet, hg = 395 feet, Dg = 51.96 MM, Dfe = 50.90 MM, D = 127.50 To find eleva- tion of ”b" dh = (10,000 - 395) (51.96-50.90) ^ (9605) (1.06) ^ 127.50 - 51.96 75.54 hb = hg + dh = 395 + 135 = 530 feet The parallax equation may also be used to compute II, If the elevation of two points are known. For example, using above data to find II: 134.8 = (H -395) (1.06) ^ = 10,000 75.54 412.3 CORRECTION OF PARALLAX MEASUREMENTS FOR PHOTO DISTOR- TION. The difference In elevation as computed In Article 412.2 Is cor- rect only If the photos are free from distortion due to tilt or proces- sing, or to Incorrect orientation In mounting the stereo pair. Correc- tion for a warped datum plane can be made using the following formulas; Difference In parallax measurement. dPx = (D-Dx) hx II Parallax measurement to datum, Dd - Dj^ + p^ Example; Given parallax measurements for three points of known elevation; a dPa = dpb = dpc = .96, Dg = 50.90, Dc (127.50 - 51.91) = 51.20, 395 D = 127.50, II = (75.54) 10,000 395 = 2.98 10,000 10,000 (127.50 - 50.90) 536 = (76.60) 536 = 4.11 10,000 10,000 (127.50 - 51.20) 472 (76.30) 472 = 3.60 10,000 10,000 88 D at datum for a = 51.96 + 2.98 = 54. 9A D at datum for b = 50.90 + 4.11 = 55.01 D at datura for c = 51.20 + 3.60 = 54.80 The computed parallax measurements at datura are not constant, indicating a warped datum plan. Select an assumed Dd. This is acceptable since it is the correction for parallax differences between two points that is required. Differences will be the same regardless of the Dd used. CORRECTION TABULATION FORM H = 10,000 ft. D = 127.50 MM Point Dx D-Dx hx+H dpx Com- outed As- sumed Correc- t ion Correc ted a 395 51.96 75.54 0.0395 2.98 54.94 55.00 +0.06 52.02 b 536 50.90 76.60 0.0536 4.11 55.01 55.00 -0.01 50.89 c 472 51.20 76.30 0.0472 3.60 54.80 55.00 +0.20 50.40 The correction (Column 9) can be applied to the of any other point ”x” in the vicinity of a corrected point to correct for a warped datum plane. If a number of points of known elevation are distributed over the photo overlap, a correction Isogram can be made on a transpar- ent overlay. Interpolated correction lines are drawn in the same man- ner as isobars on a weather chart. 412.4 DISTANCE BSTI7EEN CONTROL POINTS BY RADIAL LIME PLOT. If a Kail or other mechanical plotter is available, the distances be- tween control points may be found by plotting the control points and scaling the distances. Otherwise the following radial line plot method is suggested: 1. Orient a stereb-palr of photos so that flight lines are in perfect alignment and the distance from CP2 to CPi = tPPl to C^^_+ (CPi to PP2) 2 2. On a sheet of detail drawing paper or a transparent overlay, draw radial lines from PPj through road control points. 3. Draw radial lines from PP2 through the same control points, intersecting the radial lines drawn from PPj. The inter- sected points win then be in their correct relationship to each other, as on a map. 4. Scale the distance between the plots of adjacent control 89 points. The plot scale Is three times the average photo scale, computed at principal points, (because PPi to PP2 = 3 times CP2 to CPi). The photo scale R.F. measurement . lens focal length flight height above ground in the same units of The focal length of the lens is shown on the terminal photos of the flight strip. If a ground distance is known, compute R.F. from Photo distance . ground distance FIGURR 412-2 RADIAL LINE PLOT 90 The photo scalo in feet to the Inch = flight height above ground f 5. If the route between control points is not an approximately straight line which can be scaled, measure the distance under the stereo- scope with a '”tap Measure” (which has a measuring wheel and dial) or step off the route distance with dividers, follovrine the approximate grade contour. Than, by proportion, the approximate route distance between two control points = radial plot distance x photo route distance photo straight line distance The radial line plot method is Illustrated in Figure 412-2. 412.5 PLOTTING GRADE LINE ON PHOTOS, If it is desired to plot points along a grade line between control points, compute the parallax measurement ”Dx‘* for the elevation of each intermediate point ”x”. Example: Using the data given in example under 412.3, the dis- tance between control points ”a” and ”b”, which are 141 feet, the difference in elevation is measured as 2,800 feet, then the grade between control points is 141+2,800 = 5%. The elevation on grade at a point ”x”, halfway between control points, would be (395+536)/2 = 465 feet. The ”Dx” for point ”x” = (52.02 + 50.89)/2 = 51.45 131. The point between control points is found by trial to have a distance of 51.45 1?M between the Images of the point at 465 feet elev^atlon. If a long grade line, such as a maximum sustained grade along a hillside, is to be plotted, the Bureau of Public Roads method of photo- gramraetrlc route projection (Article 412.7) is preferable. 412.6 MEASURING ELEVATION DIFFERENCES BY TEMPLET METHOD. Goodale(3 /) gives a rapid method by which parallax measurement to 0.1 MM give height differences within a range of + 10 percent.* *It does not require photo scale, flight height, or any known elevation. It does require a map distance measurement, ”Bm” between principal points apd the focal length ”f” of the lens. 1. A templet is prepared by placing a sheet of transparent ma- terial, such as Dupont ’*Mylar”, over the right-hand photo. With a fine-pointed needle, mark on the templet the prin- cipal points, and the two points for which difference in elevation is desired. Trace the base line between principal and conjugate points. 2. The templet is then placed over the left photo with the lower elevation point on the templet coinciding with the same point on the photo. Pivoting on the lower point, the templet is swung so that the base line on the templet is either superimposed or parallel to the base line on the photo. (If tilt or difference in photo scale due to dif- ference in flight height, the base lines will not coin- cide and so are swung parallel.) 91 3. The principal point of the left photo is marked on the base line on the templet. The distances, "bj*' between the two principal points on the templet is measured. This is the photo base adjusted to datum of lower elevation point. 4. The upper elevation point on the left photo is marked on the templet. 5. Operations 2, 3, and 4 are repeated with the upper eleva- tion points in coincidence. This gives a new principal point position of the left photo along the base line, and a new position of the lower elevation point. The parallax difference, ”dp*', between all three points is measured on the templet; (a) between the two principal point posi- tions of the left photo along the center line, (b) be- tween the two upper elevation points, and (c) between the two lower elevation points. If there is no tilt or error, the three measurements will be equal. If tilt exists, the **dp" least affected by the tilt (perceivable in stereo view) is used. 6. The difference in elevation "dh” is computed from the form- ula: dh = (dp) (f) (Bm) bj (bj^ + dp) Example; Given dp = 0.05”, f = 8.25", bi = 3.33" dh = 0»03 X 8.25 x 4,400 3.33(3.33 + 0.05) Bm = 4 , 400 = 1.815 11.25 feet and = 161 feet If differences in elevation between a number of points are de- sired, the point of lowest elevation, is used as the datum. A single measurement of "b", serves for allppoints, and all dif- ferences in elevation are computed from the lowest point. 412.7 BUREAU OF PUBLIC ROADS METHOD OF PHOTOGRAMME TRIG ROUTE PROJECTION. The accompanying "Photograrametr ic Work Sheet" is the form used by the Bureau of Public Roads for making compu- tations for projecting road routes on aerial photos. The formulas used are; h = ™ p = hh h = b + p H-h b Scale in feet per inch, S = f where "H" = flight height above datum in feet "h" = image point elevation above datum in feet "b" = distance between principal point and conjugate point on each photo (air photo base) in millimeters "d" = parallax distances between two images of the same point . in millimeters 92 FIGURE 412-3 ELEVATION DIFFERENCE BY TEMPLET METHOD x= Elevation Point on Photo 0= Elevation Point on Photo L= Lower Elevation Point U= Upper Elevation Point PHOTO 1 PHOTO 2 X L, PP, CP2 CP| PPo -1 (- + + X U, X U2 PHOTO 1 Templtf 0 L|L2 0 Lg -t- ft-*- U — b,--? U20*U| 0 U2 PHOTO 1 L| X OL2 Templet ■H »o ® U| U2 93 9 9 DEPARTMEKT OF COMMERCE BUREAU OF PUBLIC ROADS PHOTOGRAMMETRIC WORK SHEET h P H b ♦ p p(H-h) h «= b H - h S » = (ft. per in.) f Photographs No. _ Flight Altitude _ Flight Height (H) b to P. O. BOX MOO POK1XAND a. OR Sheet of Sheets Date Project - — _ No. Section Instruments Location Engineer IMAGE POUT d FOR PARALLAX PARALLAX P h FROM DATUM H - h SCALE FT. TO 1 IN. (8) DISTANCE BETVEEN IMAGE POINTS GRADE t STATION ELEV. REMARKS VERTICAL HORIZONTAL IN. FT. ON V "p" = difference in feet between "d" for base point of known ele- vation and ”d” for point of unknown elevation. A positive sign for ”p" and "h” indicates a higher point of unknown elevation, a negative sign a lower elevation. Computations for "h" or "p" are based on the larger of the two photo bases ”b”. The procedure followed by the Bureau of Public Roads photogram- metrist is to lay out the photos by flights and study them for possible routes and control points. An approximate route between control points is then marked by a dotted line by eye under the stereoscope. Computations for grade line are customarily made by one inch increments ofophoto dis- tance and the grade points plotted. After about five elevation points have been computed, a check back to the base elevation is made. If the grade elevations are starting to diverge, the ensuing projection is modified accordingly. To "turn" the route projection to an adjacent flight, the last elevation point is transferred to the side-lapped photo of the adja- cent flight. This elevation point is used as the starting point for pro- jection on the adjacent flight photos. It is preferable to make the pro- jection downgrade, for the same reasons that a reconnaissance grade line is run downgrade. (Article 423.2) The route connecting grade points is marked with a solid line. Example: Given: Flight altitude = 19,000 ft., flight height H = 14,000 ft. known elevation h = 5,000 ft. and b = 158.2. Elevation of starting point "0" is com- puted as follows (slide rule precision). Parallax distances measured with 50 scale. Parallax distance for point "0" 460.1 Parallax distance for 5000* elevation 451.9 h = P H b+p -8.2 x 14,000 -1148 P = -8.2 = -765 158.2 + (-8.2) 150 H - h = 14,000 -(-765) = 14,765 S = __ II - h = 14, 765 = 2,460 ft. per inch f 6 Elevation of point "0" = 5,000 - 765 = 4,235 Computations for point "1" for 1 inch photo distance on a + 6% grade. Since elevation will be higher, scale "S", in feet to the inch will be smaller. Assume S = 2,440 ft/lnch. Then 67. x 2,440 = rise of 146 ft., say 145 to nearest 5 ft. Elevation of point "1" = 4,235 + 145 = 4,380 h = 5,000 - 4,380 = -620 H - h = 14,000- (-620) = 14,620 95 bh H - h 158.2 X (-620) 14,620 -98,000 14,620 -6.7 P = d = 451.9 - (-6.7) = 458.6 Check on scale S = = 2,437 vs. 2,440 assumed. Correct 6 to nearest 10 ft. distance. The point at 1 inch photo distance which has a parallax distance of 458.6 will have an elevation of 4,380 and will be on a 6% grade line. Computations for point "2” at 1" distance on a +6% grade. Assume S = 2,420. Then 67. x 2,420 = 145 ft. elevation at point "2" = 4,380 + 145 = 4,525. h = 5,000 - 4,525 = -475. H - b = 14,000 - (-475) = 14,475. Check on scale S = 14,475/6 = 2,410. 6% X 2,410 = 144.6 = 145 ft. elevation OK 158.2 X (-475) _ -75200 ^ , P " T47475 14,475 d = 451.9 -(-5.2) = 457.1 412.8 SLOPE MEASUREMENT FOR COST COMPARISON. An approximate cost comparison of alternate photo-projected routes can be made by deter- mining side slopes on the photo and estimating quantities and construc- tion costs in the same way as given in Article 411.6. Side slopes may be determined by computing horizontal distances and differences in elevation between points on each side of the route by any of the previ- ously described photogrammetr Ic methods, or by use of special instru- ments such as the ’’Stereo Slope Meter.” Choate(l^^ gives a rapid method of determining slope percent with a parallax bar and a table of ’’Differential Parallax Factors.” The photo scale is not required. A lower point and an upper point on the slope are selected. The photo distance in thousandths of feet between the two points is measured. The parallax distance between two points is measured to 0.01 mm. with the parallax bar. This measure- ment is converted to feet elevation difference (to the nearest .001) by using the table of ’’Differential Parallax Factors.” Then, Slope 7. = Parallax Difference in feet x 100 •pPhoto distance in feet between points If elevation differences exceed 200 ft. the parallax formula should be used. If the points fall outside of the range of elevations of the principal point and the conjugate point, use the average of the distances between the elevation points and their conjugate images, measured parallel to the flight line, as the photo base, instead of the distance between principal and conjugate points, when entering the table. 96 Example; Given parallax distance 1.27 ram.; photo distance 0.25 inch = 0.021 feet; distance PP to CP 3.30 inches; f = 8^ inches. Differential parallax factor, from table 127 X 0.000082 = 0.0104 Slope 7o = = 49.5, say 507. 0.021 0.000082 The Differential Parallax Factor Table may also be used to ob- tain elevation differences when photo scale is known. Example; Scale R. F. = 1 ; 15,840 Elevation difference = .0104 x 15,840 = 165 ft. 0.25 in. at 1 ; 15,840 = 3,960 in. = 330 ft. Slope = ^ = 0.50 = 507. Study of Problem 12--Measuring slope percents, and Problem 13-- Road planning on photos, in reference (2^/) is recommended. This reference was supplied to all district offices June 7, 1960 by the Director, Bureau of Land Management . 97 DIFFERENTIAL PARALLAX FACTORS (1/) Elevation Differences in Feet per .01 mm of Parallax Difference RF = 1 ; 1 Distance between PP & CP 00 11 f = 12*» 2.0 •’ .000135 .000197 2.1 .000129 .000187 2.2 .000123 .000179 2.3 .000118 .000171 2.4 .000113 .000164 2.5 .000108 .000157 2.6 .000104 .000151 2.7 .000100 .000146 2.8 .000097 .000141 2.9 . 000093 .000136 3.0 . 000090 .000131 3.1 .000087 .000127 3.2 .000085 .000123 3.3 .000082 .000119 3.4 . 000080 .000116 3.5 .000077 .000113 3.6 .000075 .000109 3.7 . 000073 .000106 3.8 .000071 .000104 3.9 .000069 .000101 4.0 .000068 . 000098 4.1 . 000066 .000096 4.2 .000065 .000094 4.3 . 000063 .000092 4.4 . 000061 .000089 4.5 .000060 .000087 4.6 .000059 .000085 4.7 .000057 .000084 4.8 .000056 .000082 4.9 .000055 .000080 98 420 FIELD RECONNAISSANCE 421 INTRODUCTION 421.1 DEFINITION. By reconnaissance is meant the reconnoiter- ing of the terrain in the field to determine a road route or to check a projected route. It includes all the field work preceding the preliminary or location survey in which angles or bearings are measured, distances taped and stakes set. Reconnaissance implies thorough investigation and analysis. The reconnaissance is completed when the final route has been determined, within narrow limits, and the grade line marked between con- trol points. The major decisions affecting the route have been made and only minor adjustments may be required during the survey. The reconnais- sance generally is made in two stages: 1. The extensive reconnaissance. This is a reconnaissance of area and major controls, embracing a relatively wide belt of land. The extent of the extensive reconnaissance will depend upon how much reliable information is available from maps and aerial photos. 2. The intensive reconnaissance. This is a reconnaissance of a selected route and minor control points. It embraces a narrow belt of land and establishes the line for the road survey. 421.2 OBJECTIVE OF THE RECONNAISSANCE. The objective of the extensive reconnaissance is to eliminate unfeasible routes and to decide upon the best route. The best route is the most economical route which serves the purposes for which the road is to be built. It is the route which will result in a road neither above or below the standards estab- lished for the class of road. If the route has been projected on large scale maps or aerial photos the initial reconnaissance will check the validity of the projected route. Control points may be encountered which did not show on the map or photo, necessitating changes in the projected route. Finding gravel deposits or pit-run rock for surfacing is another objective of the extensive reconnaissance. The objective of the intensive reconnaissance is to mark on the ground the line which the survey is to follow. Usually a tagged or flagged grade line is run between control points. 421.3 IMPORTANCE OF THE RECONNAISSANCE. The importance of the reconnaissance cannot be overemphasized. It is during the reconnaissance that the major decisions should be made. The construction and maintenance costs, the transportation costs and the utility of the road are all af- fected by the reconnaissance. Good reconnaissance will avoid changes having to be made during the location survey, at greater cost than if made during the reconnaissance. Mistakes made during the reconnaissance are often difficult and expensive to correct later on. Reconnaissance is hard work. The successful forest road engineer does not ’’give up” easily. He does not accept the first and most obvious route as ’’good enough” and fall to investigate all possible alternate routes. There is nor, substitute for ”leg work” on reconnaissance. 99 Experienced forest engineers generally consider the reconnais- sance to be the most Important part of their work. The subsequent survey and design is viewed as relatively routine. Ample time should be scheduled for the reconnaissance. Saving reconnaissance expense is unimportant compared with the savings in road costs and vehicle operating costs obtainable by allowing enough time to determine the best route. A21.4 SEASONS FOR RECONNAISSANCE. Weather conditions permit- ting, the best seasons of the year to make the reconnaissance are late autumn, after the deciduous leaves have fallen, winter, and early spring before the brush is in leaf. Visibility is greater and a wider belt of terrain can be seen. Tag lines can be run more efficiently as longer Abney sights can be taken and less time is wasted trying to find the sighting mark. A background of experience in road location and construction is highly desirable for the reconnaissance engineer. Such experience will enable him better to visualize the constructed road along the route and avoid mistakes. The ideal program for the forest road engi- neer would be to spend the late spring, summer and early autumn on loca- tion and construction engineering, the periods of winter when weather precludes field work on route projection, and the other seasons on recon- naissance. A22 RECONNAISSANCE FOR UNPROJECTED ROUTE 422.1 EXTENSIVE RECONNAISSANCE. When the road route has not been first projected on large scale maps or aerial photos, an extensive reconnaissance precedes the Intensive reconnaissance. Prior to going into the field, assemble all available small scale maps such as U.S.G.S. topographic quadrangles, and geological maps, and such maps of adjacent or intermingled private lands as are obtainable. Study these maps and the aerial photos of the reconnaissance area to find possible routes to investigate, and to plan the field work. Plan the extensive reconnaissance so as to cover the belt of land embracing the possible routes in a systematic manner. Take the map and photos into the field. Whenever an identifiable section line is crossed, run a hand compass and pacing tie to a corner to fix your posi- tion. Keep track of direction by hand compass, of distances by pacing, and of elevations at identifiable points or at possible control points by aneroid barometer or altimeter. Mark them on the photos. Do not depend upon memory to compare alternative routes. Keep notes on the left hand pages of Field Book Form 301 and strip map sketch with form lines on the right hand pages. It is helpful in making the decision on the route for the intensive reconnaissance to build up a sketch map on 10 x 10 cross-section paper. The high cost of surfacing of roads in some districts points to the desirability of keeping a sharp lookout for rock suitable for sur- facing. 100 If the reconnaissance is for timber sale roads, keep the lo"<»inrr plan in mind. The road reconnaissance must be correlated with the lo