PUBLIC ROADS

A JOURNAL OF HIGHWAY RESEARCH U. S. DEPARTMENT OF AGRICULTURE

BUREAU OF PUBLIC ROADS

CERTIFICATE: By direction of the Secretary of Agriculture, the matter contained herein is published as administrative information and is required

VOL. 6, NO. 3

for the proper transaction of the public business

MAY, 1925 H. S. FAIRBANK, Editor

TABLE OF CONTENTS

The Maine Highway Transportation Survey A Preliminary Report

The Wagon and the Elevating Grader . : Part II.—The Influence of Design on Elevating Grader Costs

THE U. S. BUREAU OF PUBLIC ROADS Willard Building, Washington, D. C.

REGIONAL HEADQUARTERS, Bay Building, San Francisco, Calif.

DISTRICT OFFICES

DISTRICT No. 1, Oregon, Washington, Montana, and Alaska. Box 3900, Portland, Oreg.

DISTRICT No. 2, California and Nevada. Bay Building, San Francisco, Calif.

DISTRICT No. 3, Colorado and Wyoming. 301 Customhouse Building, Denver, Colo.

DISTRICT No. 4, Minnesota, North Dakota, South Dakota, and Wisconsin.

410 Hamm Building, St. Paul, Minn.

DISTRICT No. 5, Iowa, Kansas, Missouri, and Nebraska.

8th Floor, Saunders-Kennedy Bldg., Omaha, Nebr.

DISTRICT No. 6, Arkansas, Louisiana, Oklahoma, and Texas. 1912 F. & M. Bank Building, Fort Worth, Tex.

DISTRICT No. 7, Illinois, Indiana, Kentucky, and Michigan. South Chicago Station, Chicago, Ill.

DISTRICT No. 8, Alabama, Georgia, Florida, Mississippi, South Carolina,

and Tennessee. Box J, Montgomery, Ala.

DISTRICT No. 9, Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, and Vermont. Federal Building, Troy, N. Y.

DISTRICT No. 10, Delaware, Maryland, North Carolina, Ohio, Pennsylvania, Virginia, and West Virginia. Willard Building, Washington, D. C.

DISTRICT No. 12, Idaho and Utah. Fred J. Kiesel Building, Ogden, Utah.

DISTRICT No. 13, Arizona and New Mexico. 242 West Washington St., Phoenix, Anz.

Owing to the necessarily limited edition of this publication it will be impossible to distribute it free to any persons or institutions other than State and county officials actually engaged in planning or constructing public highways, instructors in highway engineering, periodicals upon an exchange basis, and Members of both Houses of Congress. Others desiring to obtain “Public Roads’ can do so by sending 10 cents for a single number or $1 per year to the Superintendent of Docu- ments, Government Printing Office, Washington, D. C

THE MAINE HIGHWAY TRANSPORTATION SURVEY

A PRELIMINARY REPORT

BY THE DIVISION OF HIGHWAY TRANSPORT AND ECONOMICS, U. S. BUREAU OF PUBLIC ROADS Reported by J. G. McKAY, Chief of Division, and O. M. ELVEHJEM, Highway Economist

PRELIMINARY analysis of the evidence ob- tained in the Maine highway transportation survey, conducted by the United States Bureau

of Public Roads in cooperation with the Maine State Highway Commission has developed a number of interesting and useful facts with regard to the traffic on the Maine highways, its growth over a period of years, present distribution over the State system, probable future density, and other matters of interest generally to all concerned with the planning and con- struction of highways. The evidence analyzed was recorded in the course of the field study which was begun July. 1, 1924, and lasted until October 31, 1924.

The rapid increase in the demand for highway service is indicated by the increase in motor vehicle registra- tion and in the traffic on the State highway system from 1916 to 1924. Between 1916 and 1920 the regis- tration doubled, it doubled again from 1920 to 1924, and it is estimated that it will double again from 1924 to 1930. Parelleling this increase, the traffic doubled between 1916 and 1919, it doubled again from 1919 to 1923, and it is estimated that it will double again in the period from 1924 to 1930. But while the demand for highway service in the State, considering the trans- portation of passengers and commodities together, has thus apparently doubled and redoubled in the past eight years, consideration of the motor-truck and passenger-car traffic separately suggests that there is a difference, so far as the State highway system is con- cerned, in the demands for motor-truck and passenger- car transportation. This is evidenced by the fact that truck traffic has increased at a slower rate than truck registration, while passenger-car traffic has increased at a faster rate than passenger-car registration; but, for total vehicles, the rates of increase of highwa traffic and vehicle registration have been nearly equal.

One of the most valuable results of the survey is the collection of data upon which future traffic may be forecast with reasonable accuracy. This makes pos- sible the development of a definite program of future improvement by determining the routes to be improved, the order of their improvement, and the type of im- provement required. The forecast of future traffic is of particular value in Maine since the State has reached the second critical stage in the development of its high- ways. Hitherto the highway commission has wisely constructed large mileages of gravel roads to make accessible the greatest possible area of the State with the funds available.

The concentration of motor-vehicle traffic around the centers of population on the principal State roads now makes necessary a definite improvement policy governing the selection of the routes to be recon- structed with surfaces of higher-type, and the deter- mination of the type of surfacing. The Maine experi- ence indicates that a gravel road will not successfully carry over 500 vehicles per 12-hour day without resort- ing to surface treatment.

Application of the most reliable available informa- tion with regard to the savings in operating costs of vehicles made possible by improvement in road sur- faces indicates that, on the basis of present traffic, the

45029—25},——1

300 miles of most heavily traveled roads in the State could be improved from an earth-road condition to a condition in which every mile would be surfaced with concrete, and the entire cost of the improvement, with interest at 4 per cent, would be repaid by the savings in operating costs of passenger cars only in slightly over four years.

SEVEN PER CENT OF THE ROADS SERVE TRAFFIC

MORE THAN HALF THE

The survey has brought to light a number of in- teresting facts with regard to the traffic on the roads of the State. For example, it is shown that the primary highway system which embraces only 7.1 per cent of the total highway mileage carries 53.4 per cent of the total daily vehicle mileage. Furthermore, 18.4 per cent of the primary system carries 38.7 per cent of the total daily vehicle mileage on the system. From this it follows that, with respect to the entire highway sys- tem of the State, 1.3 per cent of the total mileage serves more than a fifth of the traffic, as measured in vehicle miles.

It is evident that the heavy concentration of traffic is confined to a relatively small percentage of the total highway mileage. For this reason it is advocated that traffic zones should be created to bring together for construction and maintenance purposes those sections of the highway system which serve approximately the same amount and type of traffic.

The traffic importance of the primary system as compared with the secondary system appears even greater when considered from the point of view of motor-truck traffic than when considered from the standpoint of passenger-car traffic. Practically all trucks using the Maine highways have capacities between one-half and 2% tons, and the number of trucks of 5 tons capacity or over is practically negli- gible. Over 80 per cent of the trucks observed were equipped with pneumatic tires, and from 55 to 67 per cent were loaded. Wheel loads in excess of 2,500 pounds were found to be very exceptional on trucks weighing less than 6,000 pounds gross, and the maxi- mum wheel load for trucks of less than 12,000 pounds gross weight (3 tons capacity) was found to be 5,000 pounds. Over 98 per cent of such trucks, however, aes wheel loads less than 4,500 pounds.

On a vehicle-mileage basis it is found that a con- siderable portion of the cost of providing highway service on the primary system is due to its use by foreign vehicles. But these vehicles pay into the State treasury through the gasoline tax a sum which the State would not receive if there were no gasoline tax, and the amount of the tax paid is proportional to their use | of the system. The use of the State’s roads by foreign motor trucks is much less extensive than its use by foreign passenger cars and, except near the State line and on a few major highways, is negligible.

As a result of the survey a forecast traffic map has been prepared which shows the anticipated density of traffic on roads of the State’s primary and secondary systems between July and November, 1930. Neglect- ing such factors as the effect of major mechanical im- provements of automobiles, it is believed that the

(45)

actual traffic in 1930 will closely approximate the estimated traffic as recorded on this map, and the map has therefore been used as a basis for a number of detailed suggestions with regard to the program of highway improvement up to 1930.

TRAFFIC ON PRIMARY, SECONDARY, AND THIRD-CLASS HIGHWAYS

There are 23,104 miles of highway in the State. Of this mileage 1,630 miles, constituting the State high- way system, is defined as the primary system. State- aid highways, consisting of 4,049 miles not included in the State highway system but serving as feeders to it, are defined as the secondary system. Third-class roads, comprising 17,425 miles, include all highways not included in the State or State-aid systems.!

This classification of the roads, it was one of the purposes of the survey to check by a more exact determination of the traffic served by them. At the same time the survey methods were designed to supply the information needed to decide upon the adequacy of the types of surfaces laid on roads of the three systems with respect to present and probable future traffic, and to serve as a paces for the equitable parti- tion of funds available for construction and main- tenance.

To serve these purposes it was necessary that the

survey supply four general classes of data, as follows::

(1) Density of traffic on all parts of each system; (2) the size and loading of motor truck traffic; (8) vehicle- mileage per year on each of the three systems; and, (4) the probable growth of traffic over a reasonable future period.

The traffic classification of roads and the selection of the most suitable type of highway surface to serve traffic depends upon the type of traffic units as well as the number of these units. The more important considerations are: (1) Density of present and future total traffic; (2) the ratio of trucks to total vehicles; (3) the proportion of trucks of large, medium, and small capacity, and the resulting gross loads; (4) the maxi- mum wheel loads; and, (5) the frequency of critical gross loads and wheel loads. In individual cases other factors must also be considered, but in general the more important considerations are those above men- tioned. ‘The final selection of type of highway surface depends upon certain physical considerations, such as availability and cost of materials, as well as upon traffic considerations.

Vehicle mileage involving, as it does, the factors of number of vehicles and mileage traveled serves as the basis for the equitable allocation of funds in propor- tion to the utilization of the three systems; and the extension of the curves of traffic and vehicle registra- tion makes possible a forecast of the growth of traffic which will enable those in charge of highway adminis- tration to make the necessary provision for future maintenance and construction.

Density of traffic on the three systems.—The density of traffic,’ which is one of the criteria determining the

1 Chap. 25, Sec. 5, Laws of Maine, 1917.

2 In this report certain terms, frequently used, have invariably the same meaning. ‘These terms and their definitions are as follows:

Vehicles refers only to motor vehicles (passenger cars and trucks) exclusive of horse-drawn conveyances.

Traffic is defined as the movement to and fro of vehicles over a highway.

Density of traffic is defined as the number of motor vehicles passing any given point on a highway in a unit of time. Unless a different unit of time is specifically stated it refers to the number of vehicles passing any given point on a highway during a day of 24 hours.

Daily refers to a day of 24 hours.

Vehicle-mile is defined as the movement of a vehicle 1 mile.

Vehicle-miles per mile is defined as the sum of the mileage traveled by all motor vehicles in passing over 1 mile of highway. Itis numerically equivalent to the average density of traffic on the mile of highway.

classification of roads and the types of surface needed, has been computed from the number of vehicles passing each of the survey stations during the observation periods corrected for each station to a 24-hour day.’

Computed in this way the average density of traffic on the three systems, as now designated, is shown in Table 1. Considering each of the systems as a whole the table indicates that the average density of traffic on the primary system is thirty-six times as great as on the third-class system and over four times as great as on the secondary system; and, as shown in Table 2, this same relation apples approximately to the truck and passenger-car traffic separately as well as to the total traffic, from which it follows, also, that the relative. density of motor-truck and passenger-car traffic on the three systems is approximately the same, the ratio in each case being about 1 to 10.

TABLE 1.—Average density of traffic on the primary, secondary, and third-class highway systems, July 1 to October 31, 1924

Index of relative density of traffic (third class= 100 per cent)

Average density

Highway system of traffic

Vehicles per day | Per cent

Primary: (16380 :mii1es) es 22 ees eee ee eee Se eee 1,044 3, 600 Secondary-(4,049 miles) foe ee ee eee ee ee ee ees 244 840 ‘Ehird:class (7442600 es)) eee: ee aa eee eee eee eee eer 29 100

TABLE 2.—Average density of motor-truck and passenger-car traffic on the primary, secondary, and third-class highway systems, July 1 to October 31, 1924

Other things being equal, these indices describe the relative average highway requirements of the traffic on the three systems and govern the average expendi- tures which may justifiably be made for the improve- ment of each mile of each system. ‘Thus, if the ratios of motor trucks to passenger cars is approximately the same, the fact that the average density of traffic on the primary system is thirty-six times as great as the aver- age density on the third-class system means that the average justifiable expenditure for the improvement of each mile of the primary system is thirty-six times as great as the average expenditure which can be justified for each mile of the third-class system.

Traffic served by the three systems.—These indices also indicate the relative transportation service afforded by each mile of the three systems, but by reason of the different extent of the systems they do not describe

3 The accuracy of the determination of density of traffic is influenced by the dis- tance between the survey stations. Exactness of method would require a density record for each point on the highway system where traffic varies. The cost involved in proportion to the relatively small gain in accuracy does not justify the location of recording stations at close intervals. The density computed for each station on the ene erat system is applied to sections of the system reasonably adjacent to each station.

the relative magnitude of the service rendered by the systems or their relative total utilization considered as

arts of the whole system of the State. This can only

e described in terms of the total daily vehicle mileage on the three systems, which is the sum of the distances traveled in a day by all vehicles on each system.‘

The importance of distinguishing between the total vehicle mileage on each system and the average density of traffic on each (which is numerically equivalent to the vehicle mileage per mile) is clearly indicated in Table 3. For, while the average density or vehicle mileage per mile on the primary system is thirty-six times the average density on the third-class system, Table 3 shows that the total traffic service rendered by the primary system, of 1,630 miles, as measured in vehicle-miles, is three and one-half times as great as the total traffic service rendered by the 17,425 miles of the third-class system. The latter relation should control the apportionment of available funds to the three systems; the former should control the justifiable expenditure per mile on each system.

TABLE 3.—Relative traffic service of the primary, secondary, and third-class highway systems

Portion Daily of total daily length ot) hgteny| istic | Saby | trattlo Highway system & Sway service poe service | system | mileage by each | Sebyice (third in each iis rendered Abee= | system y by each | 409 ner | system cent) | =~ = Se eee ee Vehicle Miles Per cent miles | Per cent | Per cent [plane ayes ee eee | 1, 6380 ad, 1, 702, 000 | 53. 4 340 POCOMMALV Resets kate loka 8 | 4, 049 17.5 | 986, 000 | 30.9 197 MEGsClasss fe 8 ey | 17,425 75.4 499, 000 | ae 100 } | |

The importance of the primary system to motor- vehicle users is evident from the fact that 53.4 per cent of the total daily vehicle mileage on all highways in Maine is found on the primary system, which includes only 7.1 per cent of the total highway mileage. The shght traffic importance of the third-class system is evidenced by the fact that only 15.7 per cent of the total daily vehicle mileage is found on this system, which includes 75.4 per cent of the total highway mileage.

In these analyses of the relations between the three systems in Maine it must be borne in mind that the re- lations both as to density of traffic and daily vehicle mileage depend upon two elements which restrict their application more or less closely to the existing situation in Maine. These elements are the existing density of

4 The daily vehicle mileage on any system is the product of the total number of vehicles operated over any part of the system during the day and the average trip mileage of those vehicles. But the total number of vehicles operated over any part of the system during the day is the sum of the densities observed at the stations on the system divided by the number of times each vehicle is counted. With any given number of stations the number of times each vehicle is counted is equal to the average trip mileage divided by the average distance between stations; e. g., if the average trip is 35 miles and the average distance between counting points is 1 mile, each vehicle will be counted on the average 35 times. : bats

The mathematical derivation of the approximate method of computing vehicle

mileage is as follows: ct , ‘ Q Dail hiel il _ (Sum of densities) (Average trip mileage) any velicle mleage= umber of times each vehicle is counted (Sum of densities) (Average trip mileage) = Average trip mileage _

Average distance between stations = (Sum of densities) (Average distance between stations)

2 .,,_., Highway mileage = (Sum of densities) Number of stations

Sum of densities . : Number of stations 1s>way mileage) = (Average density) (Highway mileage)

traffic on each mile of the Maine highways and the mileage of the three systems. Obviously, the expan- sion of the primary system by including 1,000 miles of highway now a part of the secondary system would materially change the relative daily vehicle mileage on the two systems. Similarly, a change in the mileage included in each system would also affect the average density of traffic on the three systems. The primary system, in general, now includes the more important highways of the State; the inclusion of a considerable mileage of less important highways would result in lowering the average density of traflic on the system.

It is evident, therefore, that the relationships be- tween the three systems are true only for these systems as they exist to-day, and that any change in the systems will modify the relationships; and they are applicable in other States only in so far as the factors producing highway traffic and the proportion of highway mileage in the several systems of such States is comparable with the existing conditions in Maine.

Moreover, these relationships apply only to the three systems in Maine considered as units. Analysis of the traffic on the roads included in the sytems shows that there are material differences in the traffic im- portance of roads within each system.

COMPARISON OF TRAFFIC eid Ae SECTIONS OF THE PRIMARY YST

In Table 4 traffic is analyzed on three sections of the primary system. Section | includes route 1, from Kit- tery to Belfast; route 20, from Brunswick to Fairfield; route 100, from Portland to Augusta; and route 196, from Brunswick to Auburn—a total of 300 miles. Section 2 includes route 1, Ellsworth to St. Stephan; route 15, Oldtown to Houlton; route 20, Fairfield to the north State line; and route 24, from Houlton to the north State line—a total of 467 miles. All other routes of the primary system are grouped under sec- tion 3.

TasLe 4.—Highway mileage and traffic on three sections of the primary system

From this analysis it will be seen that the average density of traffic on 300 miles of the primary system (section 1) is over four times as great as the average density on section 2, which includes 467 miles and over twice as great as the average density on the 863 miles which compose section 3. The entire primary system, which includes 7.1 per cent of the total highway mile- age, serves 53.4 per cent of the total daily traffic in vehicle-miles. But 300 miles, or 18.4 per cent of the primary system, serves 38.7 per cent of the total traffic served by the 1,630 miles of the primary system. With respect to the entire highway system of the State these 300 miles constitute on 1.3 per cent of the total highway mileage, but they serve 20.7 per cent of the total traffic.

The importance of section 1 is further illustrated by the comparison of the average daily gross tonnage per mile moved over each of the three sections of the primary system, which is shown in Table 5.

TABLE 5.—Average daily gross tonnage per mile moved over three sections of the primary system

Average daily gross tonnage per mile Section No. aie een ae Passen- | Motor r ger cars | trucks Total ase |

This table shows that in point of tonnage per mile, as well as density of traffic, section 1 of the primary system is over four times as important as section 2 and over twice as important as section 3.

Still another indication of the importance of the principal roads of the primary system is presented by Table 6, which shows the average maximum density of traffic on certain roads, as observed on panes dur- ing the period of the traffic survey, July 1 to October a1, 1924.

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Fia. 1.—Average density of all motor-vehicle traffic on principal primary and sec- ondary highways in Maine, July 1 to October 81, 1924

Taste 6.—Average maximum density of traffic on certain roads of the primary system (observed_on Sundays during the period July 1 to October 31, 1924)

Average maximum density of traffic (Sunday) Route and location of station ee Motor | Passen- trucks | ger cars Total Vehicles | Vehicles | Vehicles Route 1: per day | per day | per day South of Portland te. === ae aes Soe eee 213 | 9, 781 9, 994 Stateline (south) jes eee eee 68 6, 780 6, 848 North of Portland 2s sates ae eee ee eee 98 5, 367 5, 465 West of Brunswick____--- ae, 70 | 3, 673 38, 743 Southwest of Rockland __ 87 2, 695 2, 782 Route 20, north of Winslow _- 122 4, 357 4,479 Route 100, west of Augusta__- 82 3, 285 3, 367 Route 196: Southeast of Auburn_-- Jats 77 2, 335 2, 412 INorthsol Bruns wi Ck ese. eee ee eee 55 | 5, 182 5, 187

A recapitulation of all data indicating the utiliza- tion of the highways of the three systems is given in Table 7.

TaBLE 7.—Motor-vehicle utilization of Maine highways, July 1 to October 31, 1924

All high- Primary Secondary | Third-class ways system system system Highway mileage__________- 23, 104 1, 630 4, 049 17, 425 Percentage of highway mile- ARGe = Koh ee a Ce 100.0 | Vou 17.5 75. 4 Daily vehicle-miles: | All vehiclestasussete ses 3, 187, 000 | 1, 702, 000 986, 000 499, 000 Passenger cars_....-.---- 2, 904, 000 1, 548, 000 893, 000 463, 000 GMail aya Gang ON! 283, 000 154, 000 93, 000 36, 000 Average density of traffic:! (Aulinvehiclesuaseseaeeee 138 1, 044 244 29 Passenger cars__......-- 126 950 221 27 ED TUCKS See San = saan 12 94 23 2 Total vehicle-miles, July 1 to Oct. 31, 1924: Auli eli clesaaees ats eee 392, 001,000 | 209, 346,000 | 121,278,000 | 61,377,000 Passenger cars---.._---- 357, 192,000 | 190, 404,000 | 109, 839,000 | 56, 949, 000 RrUcks Sale eee 34, 809, 000 18, 942, 000 11, 439, 000 4, 428, 000 Percentage of vehicle miles: | Aliviehiclesies-.==—s ee 100. 0 53. 4 30. 9 15.7 Passenger cars. -..-.--=- | 100. 0 53. 3 30. 8 15.9 TUCKS oe eerie see 100. 0 54. 4 32.9 12) 7 Average daily gross tons per mile: AWivehicles: 2 = 22 en 201 T, 621 356 42 Passenger cars__--..-_-- 176 1, 330 309 38 URTUCKS Ses. see ees 25 191 47 4

1 The average density of traffic is the weighted average density per day reduced to the nearest whole number. These average values were obtained by weighting the average daily number of vehicles at each station, or group of similar stations, by the

number of miles of highway on which the daily traffic was approximately equal to °

this average, and therefore approximates the exact average obtained by summing the vehicles per day on each mile of highway and dividing the total by the number of miles of highway. ;

RELATIVE TRAFFIC IMPORTANCE OF PRINCIPAL ROADS

The relative traffic importance of the principal roads of the Maine highway system, as determined by the average density of traffic, is shown clearly in Figure 1, in which the density of traffic on roads of the primary and secondary systems is represented by the width of the lines. The chart shows at a glance which roads require the largest outlay of construction funds to provide adequate highway service.

The greatest density of traffic is found near the centers of population—Portland, Auburn, Lewiston, Augusta, Brunswick, Waterville, Bangor—and the summer-resort. district. Clearly the 300 miles pre- viously defined as section 1 of the primary system con- stitute the backbone of the entire system. These roads from Kittery to Belfast, from Brunswick to Fairfield, from Portland to Augusta, via Auburn, and from Brunswick to Auburn have, markedly, a greater den- sity of traffic than any others in the State.

Excluding ©

these and the roads from Fairfield to Bangor and from Bangor to Ellsworth and Oldtown, the average den- sity of traffic on the balance of the Maine highway system will not exceed 1,000 vehicles per day. ,

On a considerable mileage of the primary system and a large mileage of the secondary system the average density of traffic was less than 300 vehicles per day during the four months of the survey. It is anticipated that the density on these routes will not exceed 600 vehicles per day by 1930. No large expenditures will be required for high-type improvements on these roads for some years. They should receive only a sufficient amount of the construction and maintenance funds each year to meet their actual traffic needs, and the major portion of such funds should be devoted to ae immediate improvement of the heavy-traffic roads.

Clearly, there is need for the creation of traffic zones bringing together for construction and maintenance purposes those sections of the highway system which serve approximately the same amount and type of traffic and to distinguish between those routes which require constant supervision and policing to insure satisfactory service and safety to traffic and those which do not.

In the main it is evident that the primary system includes the principal traffic arteries of the State and is therefore well selected. On the basis of their traffic density, however, some roads now included in the secondary system could more properly be included in the primary system than some that are included. The roads which could well be transferred to the primary system are those from Wells to Sanford, from Portland to Standish, from Auburn to Mechanic Falls, and from Oakland to Norridgewock.

The density of motor-truck traffic on the principal roads of the primary and secondary systems is shown in Figure 2. Obviously, the principal motor-truck routes in the State are those from Kittery to Portland, Portland to Augusta via Auburn, Portland to Bruns- wick, Lisbon Falls to Auburn, Auburn to Mechanic Falls, Waterville to Fairfield, Thomaston to Camden, Bangor to Ellsworth, Bangor to Oldtown, and Port- land to Naples.

In general it will be recognized that these routes which have the largest daily motor-truck traffic are, with few exceptions, identical with those which have the greatest density of total traffic. The link of the primary system from Houlton to Van Buren via Easton and Presque Isle shows a relatively higher proportion of trucks to total traffic than is to be found on the pri- mary system as a whole. So, also, does the route from Bangor to Ellsworth, a highway urgently in need of improvement. The motor-truck capacity analysis of the road from Portland to Naples, which also shows a heavy proportion of trucks to total traffic, indicates that this road carries an unusually large proportion of the heavier trucks.

_ The general use of motor trucks on the principal traffic routes indicates the need for highway improve- ment of a type adequate to provide service for truck traffic. The fact that the highway between Bruns- wick and Waldoboro is surfaced with gravel may be, in part, responsible for the small density of, motor-truck traffic on this route. But the chart of motor-truck traffic density confirms the conclusion drawn from the discussion of the density of total traffic that high-type improvement of a considerable mileage of the primary

and a large mileage of the secondary system can safely be deferred for some years.

Sections of the secondary system which have a con- siderable density of truck traffic are the roads from Portland to Standish and from Auburn to Mechanic Falls. These roads were shown to be eligible for trans- fer to the primary system by the analysis of total traffic.

STATUS OF ROAD IMPROVEMENT IN RELATION TO TRAFFIC DENSITY

The free flow of traffic on the principal sections of the primary system is hindered by gaps of unimproved highways or sections surfaced with gravel. Between Kittery and Portland, as shown in Figures 3 and 4,

RANGELEY

FARMINGTON 52

LI} 400 TRUCKS —@IODEFOR

PRIMARY ROAD - SOLID BLACK SECONDARY ROAD-OPEN SPACE

gg hitreRY Fic. 2.—Average density of truck traffic on principal primary and secondary high- ways in Maine, July 1 to October 31, 1924

there are sections of concrete, macadam, and gravel. Sections of gravel road on a heavy-traffic route such as this do not provide adequate service to traffic and the yearly maintenance costs are excessive.

Between Auburn and Augusta, on one of the most heavily traveled routes in the State, approximately 16 of the 31 miles are gravel. Between Fennemich and Belfast there is a large mileage of gravel that undoubt- edly does not give satisfactory service to the dense traffic. Between Brunswick and Augusta, also, there are sections of macadam, gravel, and unimproved road. After improvement the density of traffic over this route can be expected to increase materially.

The routes from Bangor to Ellsworth, one direct and the other via Orland, iulustrate the need of improve- ment in proportion to the density of traffic. The direct route is gravel, although it is an important trucking

The daily variation in the number of horse-drawn conveyances was found to be much greater than the variation in motor vehicles. At different stations the proportion of horse-drawn traffic to total traffic varies

route and is also of considerable importance as a pas-

from less than 1 to 20 per cent. In general the greatest senger-car route. On the Bangor-Orland-Ellsworth

density of horse-drawn traffic was recorded at the stations at which the motor-vehicle traffic was light, although heavy horse-drawn traffic was found at some heavy motor-vehicle traffic stations which were located near towns. Extremely light horse-drawn traffic was found at some of the outlying stations which are located in undeveloped sections of the State.

| The heaviest proportion of horse-drawn traffic was |

7 te / A 7 !

i anal) He N Saatoe \FORT KENT

/ Ns

es L/ observed at stations located in well-developed agri- : Prsan see] | cultural areas which are off the main lines of motor- vehicle travel and which therefore have little motor- vehicle traffic. The horse-drawn traffic during Sep- tember and October was considerably higher at the majority of stations than it was during the months of July and August. This increase was undoubtedly due to the crop marketing movement during the early fall months.

‘ \ ‘ x or Ni 4 yi ‘f ie Sy an, x © GREENVILLE oS Bog \ of - > "4 B ee * ToPsFIELoY § ‘ al ? SS f Se vA : ee Va / Q . CALAIS) y Af QRANGELEY } ip renay G i 5 e )\ i fi & f) | UPTON \ an a a ! fe rami : rie es / Vo, LIVERMORE re, ¥ ( we a = Ps \ 2 | \ “ALLS : 2 ecurss Se Lp c Parca EE ’ 2D ie Ry q “FF ISUND FALLS | J \ a) ( 99 (2 } ) ( i C ve A 1 : \ ~ ne: ¢ n i a — y \ % 2 : \ / oo) %, oe is %, 9 GREENVILLE f \ Cc y & Or) ; d» TOPSFIELD) | ca , 4 ’ We My y te f G B ~ GORHAM | v) a IRTLAND | = 4 aa = 5000 VEHICLES | VERS ee ‘ h LEGEND oe | Xs HE concrete | Ln FES] MACADAM jqurton eas oe GRAVEL \ SAX [3] UNIMPROVET [__] secompary

Fic. 3.—Average density of motor vehicle traffic and road types on the primary sys- tem of Maine

route there is large unimproved mileage. The pas- senger-car movement and the surprisingly large motor- truck traffic over a large part of the route justifies at least a gravel surface.

In the northern part of the State the heavy trucking

is caused largely by the transportation of potatoes. | oc Aeon RES k , The average density of motor-truck traffic in this part a a “nu of the State exceeds that on a large mileage of the pri- ‘ff b ~~ Ofronruno mary system in the southeastern part of the State and | ge [__] |=400 rrucrs

Fair teny . — pine Fone

apparently justifies a higher type of highway.

LEGEND WRG concrete EEBB macapam GRAVEL [=] unimproveo 3

Fia. 4.—Average density of motor-truck traffic and road types on the primary system of Maine

MOTOR-BUS AND HORSE-DRAWN TRAFFIC

Motor-bus traffic was recorded at very few stations, and even on the routes on which busses were operated their number was negligible.

SECONDARY

ANALYSIS OF MOTOR-TRUCK CAPACITY AND WHEEL LOADS

Motor trucks in use on the Maine highway system are predominantly of the smaller capacities, from one-half to 144 tons. Even on the heavily traveled sections of the primary system practically all the trucks fall within the capacity group of one-half to 21% tons, as shown by Table 8.

TABLE 8.—Motor-truck capacities on the primary system

| Section 1 |

Table 9 presents a summary, in greater detail, of the percentages of trucks of the various capacities observed at each weight station.

TaBLe 9.—Summary of the distribution of loaded trucks by capacity groups at weight stations

| Distribution by capacity groups

Station | l

| 42 to 144 2to 244 | 3to4 | 5to5% | 6to7%

| tons tons tons tons tons

| Per cent | Per cent | Per cent | Per cent | Per cent 11) eee Berne oe oe Ss | 87. 5. 5 VERE | Sea cpee 5 ealeee se oe ra UUVAn= Sea) a pe ee eee 89. 7.6 OT Al eremee aoa eee ees GS) oat. Se ee ee ere 93. 9 5.9 PYG Cee eyelet aes So A) eee Se Rees Se 86.8 10.3 gO | Ree Senn eee ee ae LU 9 a) nt ie | 95.0 3h YF ila 0% 2h Bee AG oo SRE es ee ee 84, 3 12.3 2.8 {Oja<- pee ee AN) socers Rote te ee | 78.3 13.0 12 once eee HOS rt ee ed 81.6 12.7 4.9 35) ie ee ee AOR ose ne ak 86. 6 10.0 hil <0) ecm ee OS wy 358 Rae ae eee 89.3 9.4 OD brs Le Feel ERE ne “ilo 2 Mpa ot A ae a se a | 82.3 13.1 3.0 .5 eal CBD = | at ee ee ae 92.1 1.4 5.8 a fal aa es (OR) oS 88 nats a 93.1 6. 4 SRN see oe el ee ee EI 2 eens? bie Pa ee ee Sa 86.6 10.8 2.5 Sle) eee ee Ae eee ree LOO}(0 3 |e seen | eee eo eee 1h ae eee ee I psa ie ee Se ee 87.5 LDPE (eae = or IC Bes Cae ee See HON = «co eacepeh Ry ee | 85.9 10.0 EL |e ee renee es | ne eee I (VAs) 2) 2 Se ee ee ee eee 81.5 10.9 (UR oes eae Re eee ee i) ee SA nee oes oe aes | 92.4 4.8 QB) (areas a elles ore Os (UD = 350 ee ee re | 91.5 4.0 ONE ee oa ee

At every weight station but one (station 407) more than 80 per cent of the truck traffic consists of trucks of less than 2 tons capacity. At 7 of the 20 stations over 90 per cent of the traffic is composed of trucks of less than 2 tons capacity. Five-ton trucks are found at only 8 of the 20 stations, and the highest proportion of 5-ton trucks at any station is 1.5 per cent (station 407). Trucks larger than the 5 to 5% ton group are found at only one station (station 421), and this is undoubtedly an exceptional movement. At allstations over 90 per cent of the truck traffic is made up of trucks of less than 3 tons capacity. Station 406, although having a smaller percentage of large trucks than some of the other stations, actually has a larger number of heavy trucks per day than does any other station. For use in the control of design of pavement to meet traffic requirements these percentages should be applied to the average daily truck density.

Except at stations 407 and 408 over 90 per cent of the loaded trucks at all weight stations were under 12,000 pounds gross weight. Trucks weighing over 24,000 pounds gross were found at only two stations (stations 407 and 408), and the percentages of such trucks at these stations was very small, 0.3 per cent at station 407 and 0.1 per cent at station 408. Trucks weighing between 12,000 pounds and 18,000 pounds gross were

found at 11 of the 20 stations, but the highest per- centage of such trucks at any station was 3.4 per cent (station 407). The percentage of loaded trucks weighing less than 12,000 pounds gross agrees quite closely with the percentage of trucks of less than 3 tons capacity, as shown in Table 10.

TABLE 10.—Comparison of the percentages of trucks under 8 tons capacity and under 12,000 pounds gross load by stations

| |] Trucks || Trucks oe | epee _ Trucks under ‘ | under | 12,000 ren under 12,000 Station 3tons | pounds | Station | 3tons | pounds capacity gross | capacity gross weight | weight | Percent | Per cent Per cent | Per cent 401___ | 92. 6 93.6 || 421_ 95. 4 | 96. 5 A) De ee ene 97.3 95. 5 || 422_ 93. 5 95. 0 403 eae 99.8 98.3 || 423_ 99. 5 99. 5 404___ 97.1 96.0 || 424_ 97.4 97.2 405 scae seers 98. 7 98.9 || 425_ 100. 0 100. 0 406_ 96. 6 OSes WAGs ey ee oes see 100. 0 99. 6 A Tie Sie ae oe 91.3 | EVAN hz by feta US MT Seay 95.9 95.8 AOR ES ee eee tert 94.3 SONOMA 28 cater Le aes oe 92. 4 100. 0 400 2 te ees 96. 6 95. 5 || 470 ee ee 97.2 99. 5 410° Sa ee | 98. 7 Oonon | 450 eae sae, oe 95. 5 100. 0

A comparison of the percentages in Table 10 indi- cates that for roads in Maine where truck traffic con- sists exclusively of trucks of less than 3 tons capacity it is fairly safe to select a type of pavement which will carry a maximum load of 12,000 pounds.

Over 80 per cent of the trucks on Maine highways are equipped with pneumatic tires. Practically all trucks weighing less than 6,000 pounds gross are so equipped, and although the percentage of pneumatic- tired trucks weighing between 6,000 and 12,000 pounds gross varies considerably with location it will average approximately 75 per cent of the total.

The observations indicate that the maximum wheel load of trucks whose gross load is under 6,000 pounds is 3,000 pounds, that wheel loads over 2,500 pounds are very exceptional, and that 95.9 per cent of the trucks under 6,000 pounds gross weight have rear-wheel loads of less than 2,000 pounds. For gross loads of less than 12,000 pounds 5,000-pound wheel loads are the maximum, and of all gross loads less than 12,000 pounds 98.5 per cent have wheel loads of less than 4,500 pounds.

PROPORTION OF LOADED TRUCKS OVER 50 PER CENT

The ratio of loaded to total trucks varies from 54.8 to 66.6 per cent. The lowest percentage is found at station 425 and the highest at station 401. Of the four stations at which less than 60 per cent of the trucks observed were loaded three are located on out- lying routes—station 425 near Columbia Falls, station 423 south of Mattawamkeag, and station 402 east of Rumford. The fourth, station 403, is on route 100 be- tween Auburn and Augusta.

The average net weight per loaded truck varies from 760 pounds at station 405 to 2,060 pounds at station 407, and the average gross weight from 3,420 pounds at station 425 to 6,180 pounds at station 407. Only two stations, 407 and 408, have an average net weight in excess of 1,600 pounds per loaded truck. These are also the only stations that show an average gross weight in excess of 5,000 pounds per loaded truck. Several of the stations of relatively heavy traffic density show very low avapee net and gross weights per loaded truck because of the ea i: of one-half-ton trucks. This is especially true of sta-

tion 406, which has a larger number of 3 to 4 ton trucks and also a larger number of 5-ton trucks per day than stations 407 or 408, but because of the large number of small trucks the average weights are low. The average trip mileage per vehicle depends very largely upon the location of the station. Stations 407, 410, 421, and 425 show average trip mileages in excess of 35 miles; stations 402, 403, and 429 show average trip mileages below 20 miles.

USE OF MAINE HIGHWAYS BY FOREIGN MOTOR VEHICLES

When it is considered that 21.4 per cent of all motor vehicles on the primary system are of foreign registra- tion, that the foreign vehicles account for an average density of traffic on the primary system amounting to 223 vehicles a day, and that these vehicles travel each day 364,000 vehicle-miles, it becomes evident that the cost of providing and maintaining adequate highways in Maine is increased by the usage of the roads by foreign vehicles.

Foreign passenger cars constitute 21.2 per cent of all motor vehicles on the primary system. They pro- duce 23.3 per cent of the total passenger car-miles on the primary system, 9.9 per cent on the secondary system, and 6.5 per cent on the third-class system. ~

Foreign motor trucks are of much less importance. They account for only 2.1 per cent of the motor- truck-miles on the primary system, 1.6 per cent on the secondary system, and on the third-class system their influence is negligible.

Detailed data on the use of the Maine highways by foreign vehicles are given in Tables 11, 12, and 13.

Foreign passenger cars form a very important part of the total passenger-car traffic at stations near the State line and also at points a considerable distance from the State line on the principal traffic routes. As distance from the State line increases the proportion of foreign passenger cars decreases. On route 1 near Kittery (station 407), 68.2 per cent of the passenger cars carry foreign licenses. Near Wells (station 1B) the percentage is 43.5, and south of Portland the per- centage is 34.5 (Table 14). North of Portland foreign passenger cars decrease to 29.2 per cent on route 1 (sta- tion 409) and 18.1 per cent on route 18 (station 408).

On route 1 the percentage of foreign passenger cars near Bath (station 405) is 27.6 per cent and near Rock- land (station 429) 18.2 per cent. On route 20, south of Augusta (station 430), foreign passenger cars are 19.1 per cent of the total traffic.

Other routes in the State do not carry as large a pro- portion, but some foreign passenger cars were found at every station located on the primary and secondary system.

Trucks of foreign registration are of less importance. Foreign trucks make up over 10 per cent of the total truck traffic at only four stations, and these are all located near the State line. Only three stations (sta- tions 406, 407 and 1B) show an average of more than 10 foreign trucks a day; only seven have an average of more than five foreign trucks a day; and a large num- ber of stations have no foreign truck traffic. The differ- ence in importance of foreign trucks and foreign passen- ger cars is indicated in Table 14, which presents data for three stations on route 1, south of Portland.

The comparative use of the Maine highway system by Maine and foreign vehicles is further evidenced by the average mileage of Maine and foreign passenger

TasLe 11.—Utilization of Maine highway systems by all Maine and foreign motor vehicles

: Total Percent- a) ae Daily vehicle- age of ot traffic vehicle- giles by, . : : State *! miles by tate an System Registration | and for- oak State and | foreign eign ve- BP K foreign vehicles, hicles | “rice | Vehicles | July 1 to oD Oct. 31, 1924 Vehicles Vehicle- Vehicle- Per cent | par day miles miles Primaryss <ss2- see Maine_-____- 78.6 821 | 1,338,000 | 164, 546, 000 ee ee ee ee Foreign ____- 21.4 223 364, 000 | 44, 800, 000 Total sates & Ree alee ele 100. 0 1, 044 1, 702, 000 | 209, 346, 000 Secondary-..--_..-..-- | Maine--___-- 91.0 222 897, 000 | 110, 363, 000 1) O23 ae eee | Foreign _-___- 9.0 22 89,000 | 10, 915, 000 TOCA. ae oe ee ee 100. 0 244 986, 000 | 121, 278, 000 Third class.....-------- Maine_--__- amass 27 471,000 | 57,879, 000 1) OS 22 ea ere aren | Foreign --_-- 5.7 2 28, 000 3, 498, 000 Total somes Se Ya i nie Rs 100. 0 29 499,000 | 61,377, 000 i}

TaBLe 12.—Utilization of Maine highway systems by Maine and foreign passenger cars

Total Percent- Wi Daily vehicle- age of of tra ffie eos ae Pe ae s ‘ State area ill pach (c ions tate an System Registration | and for- tie State and | foreign eign ve- erences foreign vehicles, hicles “a jee vehicles July 1 to c Oct. 31, 1924 Vehicles Vehicle- Vehicle- Per cent | per day miles miles Primary ses =e area Maines. sae 76.7 729 | 1,187,000 | 146, 040, 000 DO. se ee oe Foreign ____- 23.3 221 361,000 | 44, 364, 000 Motalacasa=S2 ose ess. aa eee 100. 0 950 1, 548, 000 | 190, 404, 000 Secondary__.--..-.._-.- Maine. —..-- 90. 1 199 805, 000 | 98, 965, 000 Dott. Seas 2 ae MOLelgn ase 9.9 22 88, 000 | 10,874, 000 Total ze eae St A ee eee 100. 0 221 | 893, 000 | 109, 839, 000 Third class.......-.---- Maine_____- 93.5 25| 433,000| 53, 247, 000 foe ar See a cars Foreign ____- 6.5 2 30, 000 3, 702, 000 0) fs ee Sell mee ee 5 so! 100. 0 27 463,000 | 56, 949, 000

TaBLe 13.—Utilization of Maine highway systems by Maine and foreign motor trucks

Total Percent- oe | Daily vehicle- age of of traffic Lh iioae ae by Ley es pcre State ’|! miles by ate an System Registration and for- ee State and foreign eign Ve- | Gion ve- foreign vehicles, hicles hi Alec, vehicles July 1 to Oct. 31, 1924 Vehicles Vehicle- Vehicle- . Per cent | per day miles miles Primanyone eer Maines =---- 97.9 92 150,800 | 18, 544, 000 D0 eee ee SEAS Foreign ____- 2 2 3, 200 398, 000 Totalcetse: Sones Bene 2 eee 100.0 | 94 154,000 | 18, 942, 000 Secondary..--------_--- | Maine_____- 98.4| 226 91,500 | 11, 256, 000 Do ete ae Foreign. ___- 1.6 i} 1, 500 183, 000 Trotalie aaa ee oe. Ja. eee 100.0| 23.0 —- 93,000 | 11, 439, 000 Thirdiclass 2aeeeess Se eats Leweee 100. 0 2 36, 000 4, 428, 000 eee ae AB ee ES | Foreign tac oes 428 |i So See eee eee 2 ee Tolalatete 3 ee pee 100. 0 2 36, 000 4, 428, 000

cars. Maine passenger cars average 36 miles per vehicle per trip on the primary system and 26 miles per vehicle per trip on the secondary system. Foreign passenger cars average 97 miles per vehicle per trip on the primary system and 73 miles per vehicle per trip on the sec- ondary system.

TABLE 14.—Foreign passenger cars and trucks on route 1 , south of Portland

a ae eect Foreign trucks Station | Location | Percent- | ap hi Percent- ge cha age | y age EN number number AQ Vee ots. 68.2 | 2, 540 12.8 | 17.3 | Near State line at Kittery. Ite ee ae 43.5 | 1,197 6.5 | 17.9 | Near Wells, half way from State line to Portland. AUG Ree 5S 34.5 | 1, 854 2.7 | 11.5 | Near Portland.

GASOLINE-TAX REVENUES

All motor vehicles using the Maine highways con- tribute toward the upkeep of these highways through the payment of a gasoline tax of 1 cent per gallon on all gasoline purchased in the State.

The total receipts from the gasoline tax during the period July 1 to October 31, 1924, were approximately $286,400. Assuming uniform consumption of gasoline per vehicle-mile and basing the calculation on the per- centage of vehicle mileage as observed, the amount of revenue derived through the gasoline tax from each system would be $152,900 from the primary system, $88,500 from the secondary system, and $45,500 from the third-class system.

The total receipts from the gasoline tax for the cal- endar year 1924 were approximately $522,000. Assum- ing that the percentage of vehicle-miles on the three highway systems remains throughout the year the same as during the Been of the survey (July 1 to October 31), the annual gasoline-tax revenues derived from each system are shown in Table 15, which also shows the revenue per mile on each of the three systems, as well as the revenue that could be collected from the same traffic at tax rates of 2 and 3 cents per gallon.

TasLe 15.—Annual gasoline-tax revenues by highway systems, based on 1924 revenues and traffic from July 1 to October 31, 1924

Tax of 1 cent Tax of 2 cents per | Tax of 3 cents per per gallon gallon gallon Highway system | Mile-

revenue | ZUG PEF) yevenue | BUC Per) revenue | 2Ue per mnile mile mnile All highways-__.-_| 23, 104 |$522, 000 | $22. 59 $1, 044, 000 | $45.19 |$1, 566,000 | $67.78 eMIMAry.soe.. 22 1, 630 | 279,000 | 171.17 558, 000 | 342. 33 837,000 | 513. 50 Secondary----__-_- 4,049 | 161, 000 39. 76 322, 000 79. 53 483, 000 119, 29 Hhind class=. 52 = _ — 17, 425 82, 000 4,71 164, 000 9, 41 246, 000 14, 12 | |

The forecast of traffic for 1930 indicates that traffic will double during the period 1924 to 1930. Assuming that the average annual mileage per vehicle in 1930 remains the same as in 1924 and that no radical changes occur in the rate of gasoline consumption per vehicle- mile during this period, a gasoline tax of 1 cent per gallon in 1930 will produce $1,044,000, a tax of 2 cents per gallon $2,088,000, and a tax of 3 cents per gallon $3,132,000. .

Foreign vehicles using Maine highways also contrib- ute toward the upkeep of Maine highways by payment of the gasoline tax. In Table 11 the percentage of utilization by foreign vehicles is shown to be 21.4 per cent on the primary system, 9 per cent on the second- ary system, and 5.7 per cent on the third-class system.

45029—25t——2

Assuming that the foreign traffic during the month of June is equal to the foreign traffic during the aver- age month of the period July 1 to October 31 and that during the remainder of the year it is insignificant, the gasoline tax receipts from foreign vehicles during 1924 were approximately: Primary system, $40,900; sec- ondary system, $10,000; third-class system, $3,200.

The amount of the receipts which on the same basis would be derived in a year from foreign vehicles on the three highway systems at tax rates of 1, 2, and 3 cents per gallon of gasoline are shown in Table 16.

TABLE 16.—Annual gasoline-tax receipts from foreign vehicles by highway systems, based on 1924 traffic

Tax of 1 cent per | Tax of 2 cents per | Tax of 3 cents per gallon gallon gallon

Highway system siee- ee

| | Total |Revenue| Total | Revenue} Total Feareae revenue | per mile | revenue | per mile | revenue | per mile |

$40, 900 | $81,800 | $50. 18 a

Primary ae eee $25. 09 | $122,700 | $75. 28 Secondary assess ee =e 10, 000 2. 47 20, 000 | 4.94 | 30,000 | 7.41 18 .387 | 9,600 | 55

Third class.-___.___- | 3,200 | 6, 400 | | i

IMPROVEMENT OF OLR AE eet JUSTIFIED BY TRAFFIC

Whether or not the State is economically justified in improving its roads and the degree of improve- ment warranted—these questions depend to a con- siderable extent upon the amount of the savings in the operating costs of vehicles made possible by the improvement. Assuming that the operating cost is reduced 2.7 cents per passenger-car-mile by constructing a concrete road where formerly there has been an earth road,> and applying this difference in operating costs to the average daily traffic on the heavy-traffic routes of the Maine primary system, the change in the type of construction is shown to be fully justified.

For example, the average density of passenger-car traffic on section 1 of the primary system, involving 300 miles of the most heavily traveled roads in the State, was 2,042 cars. The total number of passenger- car-miles per mile during the period from July 1 to October 31 was, then, approximately 251,000. As gasoline-tax receipts during this period were approxi- mately 55 per cent of the total receipts for the year, it is reasonable to assume that the traffic during this period was approximately 55 per cent of the annual traffic. On this basis, the total passenger-car mileage per mile of the heavy-traffic routes of the primary system for the year 1924 would be approximately 456,000 passenger-car-miles; and the saving of 2.7 cents per passenger-car-mile effected by changing the type of the road from earth to concrete would be approxi- mately $12,300 per mile. As the average cost of Federal-aid concrete roads completed in Maine up to July 30, 1924, was $45,200 per mile, it will be seen that the entire cost of building the concrete road could be retired by the saving in operating costs of $12,300 per mile in a few'years. With interest at 4 per cent the time required would be slightly over four years.

5 The difference in operating cost of 2.7 cents per passenger-car-mile is based on the researches conducted by the Iowa engineering experiment station under the direction of T. R. Agg, results of which are published in Bulletin 69, Iowa State College of Agriculture and Mechanic Arts, by T. R. Agg and H. S. Carter. The costs are tentative and are applicable directly only to the surfaces and the vehicles used in the tests. They may not express the true relation of operating costs on con- crete and earth roads in Maine, but they are the most reliable estimates available and seem reasonable,

It is believed that the 2.7 cents saving assumed above is a conservative estimate of the difference in operating costs on concrete and earth roads in Maine. But it will be noted that in the example cited the con- siderable operating savings of motor trucks, of which there were 155 a day on the heavy-traffic routes of the primary system, have been purposely ignored, as also have been savings resulting from the reduction in the cost of road maintenance. Indeed, it is highly probable that it would be impossible to maintain an earth road in satisfactory condition under the daily traffic on these

100,000

oS Se

1,000

afl _-t+——--

3 3 S319IH3A 40 YIGWAN

NUMBER OF VEHICLES

—— — PASSENGER CAR REGISTRATION ——— PASSENGER CAR TRAFFIC —-— TRUCK REGISTRATION

--— TRUCK TRAFFIC

100 OO

1922

1919 1920 192)

YEARS

10 1916 1917 1918 1923 1924

Fic. 5.—Maine highway traffic and motor vehicle registration, when plotted to a logarithmic scale, shows by the approximately equal slopes of the curves that the rates of increase of traffic and registration are nearly equal

roads which is in excess of 2,000 vehicles a day. Ex- perience of the Maine Highway Commission with re- gard to maintenance costs on the more heavily traveled highways of the State indicates “that traffic is being carried on the bituminous macadam roads at a cost one-sixth as much per vehicle-mile as is the cost of carrying traffic on the gravel-surfaced highways.’ ®

Maintenance costs per vehicle-mile on a concrete highway probably would not be higher than on a bituminous macadam highway. Combining this sav- ing in maintenance costs with the saving in vehicle operating costs, the economy of the higher-type surfaces on the more heavily traveled highways of the State becomes even more apparent.

FORECASTING OF TRAFFIC MADE POSSIBLE BY SURVEY

One of the most valuable results of a highway trans- portation survey is the development of fundamental trafic information as a basis for estimating, with reasonable accuracy, future highway traffic. A high- way traffic forecast makes possible, for the period of the forecast at least, the develo of a compre- hensive highway program including the designation of routes to be improved, the order of their improvement, and the types of improvement required. The selection of the improvement type should be based not only upon a forecast of vehicle density but also upon the weight of traffic units obtained by a motor-truck capacity and gross weight analysis. The forecast stabilizes the highway program. Uncertainty as to the growth of traffic is largely eliminated and ue high- way department is able to project a definite plan of improvement over a Soria of years based on the growth of traffic. By establishing a definite plan of improvement highway development is carried on in a more efficient and economical manner, and addition

§ Eleventh Annual Report of the Maine State Highway Commission, p. 17.

economy is effected by the elimiration of excessive maintenance costs on unsatisfactory types of highway surfaces.

It is possible by means of a forecast of traffic and registration to establish the highway budget for a reasonable period of years. Revenues to be derived from motor-vehicle license fees, gasoline taxation, and other sources of revenue can be predicted with reason- able accuracy. If such revenues, together with other available highway funds, are not sufficient to carry out the necessary program, the amount of bond issues (if the use of credit is justified in carrying out the program of improvement) can be determined. By estimating some time in advance the amount of bonds to be mar- keted in any one year (when the bond-issue method of raising revenue is necessary) 1t is possible to take advantage of the most economical market for the sale of these bonds.

GROWTH OF MAINE TRAFFIC, 1916 TO 1924

Fortunately, traffic figures are available in Maine for one week each year from 1916 to 1923, inclusive. During these years vehicles were counted from 7 a. m. to 7 p. m. for an entire week, either in the latter part of August or the beginning of September. Although the total number of stations in 1923 was 58, only 26 of these stations can be used for the whole period (1916-1923), and even in the case of these 26 stations it is necessary to interpolate some figures for the years 1916 and 1917. Beginning with 1918, however, traffic records are available for all of the 26 stations. The stations are widely distributed over the highway system, and the traffic density recorded each year is representative of the change in traffic on Maine highways from 1916 to 1923.

The average daily number of trucks and passenger cars has been computed from the week’s record at each of the 26 stations, and these daily station averages have been combined to yield average figures repre-

INDEX NUMBERS

1922

° + “ a a o

YEARS

Fic. 6.—Over the period 1916 to 1924, motor- truck traffic on Maine highways in- creased at a slower rate than motor-truck registration; passenger-car traffic during the same period increased at a faster rate than passenger-car registration

sentative of the traffic at the 26 stations in Table 17. These figures give a reliable indication of the growth of traffic over a period of years on the principal Maine highways.

Comparing with these figures the data shown in Table 18 representative of the registration of trucks and passenger cars in the State during the same period and plotting the data from the two tables to a logarith- mic scale reveals the fact that the rates of increase of

)5)

TaBLE 17.—Average daily traffic at 26 stations in Maine, 1916 to

1924 aeP) | ——_.-- : Passen- | Year | Trucks ger cars | Total

1 Figures for 1924 estimated on the basis of those stations in the 1924 traffic census which were comparable with the above 26 stations.

traffic and registration are nearly equal, as shown

by the approximately equal slopes of the registration:

and traffic curves in Figure 5. The same fact is brought out by Figures 6 and 7, in which the registration and traffic over the period are compared on the basis of index numbers derived by comparing the tabulated registration and traffic figures for each year, in one case, with the figures for 1920, and, in the other, with the average figures for the period, as a base. These charts should not be interpreted as meaning that the traffic and registration are equal throughout the series of years. They mean merely that the rates of increase of the two differ only slightly and that traffic and regis- tration are in nearly constant ratio from year to year.

Since this is so, a forecast of registration will also predict future traffic, provided there is no important change in the average annual use per vehicle. As any change of this kind must, from the nature of the case, be gradual; such a change will not greatly affect the relation between traffic and registration during the next few years.

TaBLE 18.—Registration of motor vehicles in Maine, 1916 to 1924

| | Year Trucks | ape Total UN eject ay a Se 1,991 | 28,991 30, 972 Gt een eee oan Spot oto escent enetoeen = 3,382 | 38,117 41,499 MSI) a a ee ee er 4, 200 42,372 46, 572 TNO) se Qo os Se a ee re 5, 795 47, 630 53, 425 2 ee See ee nee 8 one on wa casase cScehesn eee ce 7,512 55, 395 62, 907 DAWA See SSS eee 9, 936 67, 591 77, 527 Es Ee eee 13,842 | 78,697 92, 5389 hid Cente eens oon a. ee Os sare~cnen~sasasces 15,614 | 92,995 108, 609 i seen eee eee. eke cob a cco esesa-ascseose> 18,779 | 107, 933 126, 712

Table 19 presents the data shown in Tables 17 and 18, as indices of the average year. The graphic presentation of these indices in Figure 7 shows clearly the close agreement in the rates of increase of traflic and registration.

TaBLE 19.—Relative growth of highway traffic and motor-vehicle registration (average of years 1916 to 1923 =100)

sates Year ‘Traffic le tions 2 | 44.2 | 48.3 54.3 | 64.8 56.5 | 69.6 87.5 83.5 99.3 | 98.3 122.9 121.1 150.5 144.6 184.8 169.7 199.5 198.0

FORECAST OF REGISTRATION AND TRAFFIC, 1924 TO 1930

This relation between the rates of increase of traffic and registration may be employed to predict traffic a reasonable number of years in advance by projection of the increase in vehicle registration. Future regis- tration depends upon future population and car owner- ship per unit of population, and both of these factors can be projected on the basis of their trends over past years.

INDEX NUMBERS SH38WNN X3O0NI

TRAFFIC 0 | — — — REGISTRATION - 60

T T | 50

40 dF x0 a x0 1916 1917 1918 1919 1920 192) 1922 1923 1924 YEARS

Fig. 7.—The parallel increase in the index numbers of traffic and registration indi- cates that, considering all vehicles, the rates of increase of traffic and registration in Maine from 1916 to 1924 were nearly equal

The registration of passenger cars and trucks per unit of population in Maine from 1916 to 1924, inclusive, is plotted as a solid line in Figures 8 and 9, respectively, and trend curves projected to 1930 from these actual figures by the method of least squares are shown by the dotted lines. The results of these projections and a comparison of the computed trend with the actual figures for the period 1916 to 1924 are shown in Table 20.

TaBLE 20.—Persons per motor vehicle, 1916 to 1930

Persons per pas- Persons per senger car truck Year Faia aes a es Esti- | Esti- Actual | matea | Actual | timated NO 6 Se cee teeee oe odes on See one eae 26. 2 24. 4 381 317 aR hy pale Sey eee ea eR eee ee eS 20. 2 21.7 225 257 1 OUS tee eee Some ne ana aS em 18.0 18. 2 182 | 187 LOLS Stee eee te ee Pee a one sae 16.1 15. 4 1382 | 137 1020 See ae Ee ee a ae 13.9 13.1 102 102 ODN SS os Se eee oo a cea 11.4 | 11.3 77.7 | 78.1 QOD Be te tiaweewe seat see ta sas 9. 84 9, 81 56. 0 60. 8 ip ia ee See ee Nee eae k See iS ee 8. 36 8. 62 49.8 | 48. 1 BA 7 pa i Nai Se ey EE Ee SE ELS By ES een 7. 22 | 7. 64 41.5 | 38.6 TOZ0 22 Se ee ose anda ns oes an a aee cas en an nn le ee 6.82 pine sees a! 31.4 NO 2G ee ee a es ee a oierae ea eam eee 612i oese oe | 25.8 HKG. 7 fab A Soe Bee, Beek ER a) eh aes Ae eS ees eae © 6508 Recut sas 21.4 O28 eee eae ee eee en ees ca ae 6302) eee aee 17. 97 1990 ee ee er er een eae ace 4557) |pecteawee | 15. 18 1}! lee ee UES Be Bo ee ea eee 4.19), \eeceeeanse | 12. 92

Applying the factors of estimated persons per pas- senger car and per truck (Table 20) to the expected population, the estimated registration is obtained as shown in Table 21.

The experienced and expected rates of increase in registration are shown in Table 22. The percentage increase for each of the years 1917 to 1924, inclusive, is computed from actual registrations shown in Table 18, and the percentage increase for each of the years 1925 to 1930, inclusive, is computed from predicted registration as shown in Table 21.

TaBLE 21.—Estimated motor-vehicle registration, 1925 to 1930

Passenger-car regis- | Motor-truck regis- . . tation Gration Total registration =e Popula- meee bs " pula Aes Year tion : : , | ncrease ncrease | Increase | Number over 1924 Number over 1924 Number over 1924 Per cent Per cent Per cent E87 a eee | 779, 902 1 107, 9383 0.0 | 118,779 0.0 | 1 126, 712 0.0 192682 oes | 782,544 | 114, 740 | 6.3 24, 920 32. 6 139, 660 10.1 1026 ane ee 785, 186 128, 300 19.0 30, 480 62. 2 158, 730 25. 2 NPY fee Se es 787,828 | 142,460 32.0 36, 810 96.0 | 179, 270 41.5 19282. Paces | 790,470 | 157, 460 | 46.0 43, 990 134, 2 201, 450 59. 0 1920 eee | 798,112 | 178, 550 61.0 52, 250 178.1 | 225, 800 78.0 193802222225 795, 754 189, 920 76. 0 61, 590 228.0 | 251, 510 98. 5

1 Actual 1924 registration. From Table 21 it is apparent that motor-truck registration may be expected to increase at a faster rate than passenger-car registration. Figure 6 shows

that motor truck traffic increases at a slower rate than truck registration and passenger-car traffic in-

LEGEND

es PERSONS PER PASSENGER CAR ee ee ee ESTIMATED PERSONS PER PAS

NUMBER OF PERSONS PER PASSENGER CAR

a 2 i ce Ne aw GAIN alte Nel i a ne Eis ali les

Fia. 8.—Persons per passenger car, 1916 to 1980

NUMBER OF PERSONS PER TRUCK

364

35!

338

325

312

299

286

273

—_ |

260

247

aioeee

234

22)

208

195

182

169

156

143

oa] See] es Be SL es on a a | a es

eae Sasa

Bed

YEARS Fic. 9—Persons per motor truck, 1916 to 1930

TABLE 22.—Annual increase in total motor-vehicle registration,

1917 to 1930

Increase | Increase over pre- over pre- Year ceding Year ceding year year Per cent Per cent LOL, 2 eercdecnn ee ceeoenetasen 84.0% | 1026 seecae sateen. seceemaanees 13.7 1918. occas ade staeweaesasoane DEVE NB 52 eo oceor eae 12.9 1919.4 foc ane ssl asus ee eee es 14017 WN O28 See eae ee openers 12.4 1920 3-35 eee ee ee L767 WW! 1920 Soc eee eee coca eee 12.1 1021 S22 so ican ec otuntaaessese 93.211 1930 5 See ee 11.4 1900 ee eee eee eens 19.4 || Average annual increase 1917- 1993 S4c3 cok eee kn ace aeoeoeece 17.4 | 2A on wae ec ntoeene eens 19. 4 1994 Fe cch caste ee ee ce ease 16.7 || Average annual increase 1925- 1025 82 Seo Scsee ee eo hee eee 10.2 | 902 3 eae eee esceee 1201

creases a little more rapidly than passenger-car regis- tration; but for total vehicles the rates of increase of

traffic and registration have been nearly equal. The expected increase in total registration from 1924 to 1930 is 98.5 per cent, and, as shown by Figure 7, this rate of increase may be expected for the total traffic. Truck traffic will probably increase faster than pas- senger-car traffic but not in the ratio of the increase in registration as given in Table 21, because truck traffic on the Maine highway system has not increased as rapidly as truck registration in the State.

The expected increase in traffic of 98.5 per cent from 1924 to 1930 is applied to the 1924 traffic at all traffic stations of the 1924 survey. It is not expected that traffic at every station will increase at exactly this rate. Road improvements will modify the rate at certain stations. The opening of new routes or the development of new industries will affect the rate of increase; a new shore resort or a new route to an old resort would have considerable effect. Despite these known facts, however, a study of the traffic counts from 1916 to 1923 clearly indicates that the rate of increase at a majority of the stations varied but little from the rate of increase at all stations combined.

The expected traffic in 1930 at stations used in the 1924 traffic survey is given in Table 23. The figures are for trucks and passenger cars combined. It is anticipated that truck registration will increase at a faster rate than passenger-car registration, and the ratio of trucks to total vehicles on the road in 1930 will probably be a little greater than in 1924.

TaBLE 23.—Antictpated total traffic density in 1930 at all stations of the 1924 survey

| Total Total |) Total ae autlc ancl, : pate : pate : pate Station tranie Station traffic Station trafic density, | density, | density, 1930 | 1930 |) 1930 | | | SG/Gi C3 a eeee Bae OSS PLZOE see eesoeeese 1, 099 Gy LOSe 645-20. aaeaasSan Zoi 126A toe Seeosce 363 LOS RGOL seat oe nese ASSO it 26 13.3 seme cee 2, 014 TOG | OOzesassene sees SOGR, L2iaeessae es i lei SNG44 al G7 ee ADAH 198 ues eee eet 286 a a ee eee 1, 497M 120i ers Ne ek 504 PACD LP || S(t ieee eee ee T038:||| 1302-6 Se-n-~ = 1, 145 LOOM Piste seet ences Tall oles eee a 472 BBG || Phere en ta hotel hy ae ae ena S. 1, 552 TOGA W2es0. Ssceseces a (O20 Soneeeetas oe ene 1, 796 2s OUGa I oseee enone ee La Oy all otaee 2 seekers 1, 097 DOLE I acoenme cee ae ok 2, OSAGNL LoOneeewse ee naae 617 Pook Wl) fOssssoesee so= 2 BOOM WSO Losec Sessa se 1, 604 2 SOOM Ok are wen cot es aos L528 4022226 soe 2 1, 840 BID 09-7) len ele See a 3,005) |||$403 2552 ae sae 3, 384 S27 irl) Odeaseaaseat sane 2, DOOGI| 40425 Se eee See 5, 815 4.293) |\) 04-522 oe sono es Bb 2ban | PA00s- bese ee 3, 356 D2 240 Ob ssa ee ot SUS Se OGBY) G4 062.. See ee 11, 509 SH O0Si || 0Gsee=22 see oe SOUS 2407ss es Stes. 2 7, 661 (a) dal] het eee eee TOU WeOS ice we nares 2, 963 Glas PS whee sce BE2ANG ec ees | 6,242 TO7OUI OO pees ees se oda Al Oo sessed 3, 247 26028) LOO ee a seen n= LOD Wa2leoeos aes eee | 2,177 2. 20S aie OL ease 2a 7 80n| A22 eee ee eee sl 1, 248 2200 I, 102i 25 - soso L369 U||P423 ee eons see | 1, 733 14497) 103 Se Sees ee Se L226: ||, 424: .2S28 oe ae | 3, 918 Tit ea Ne ee 2 OC0U ALL aces sean eee! 689 O35 |#1LObeeees acess: $30) i) 426 se 8- 28 oo- =. 2, 197 (i) MU ee a 50654272 cas sees | 2, 757 Dol) Welles sone eee ee 917 Ds, ee a eee 1, 572 T8020 d2oseaenes ee | ae. Ba eee | 3, 283 HI OOO) lod een we 206 5||' 490 see eee 4, 009 1,473 |

1 Before change in location; change occurred as follows: Station 1, Sept. 28, 1924; station 126, Aug. 28, 1924. 2 After change in location.

TRAFFIC EXPECTED TO DOUBLE BETWEEN 1924 AND 1930

Summarizing the facts brought out in the foregoing discussion, it is found that Maine registration doubled in the four years from 1916 to 1920. It doubled again

in the four years from 1920 to 1924, and the forecast anticipates that it will double again during the six years from 1924 to 1930, as shown in the following tabulation:

Maine motor-vehicle registration

Year Total registration LOT GB ee See ee wi ee Boe ied 0 aS tree 30, 972 LOCU eee Bkae we Cee be ees ot ee ee le 62, 907 MM 2 Sie eee Nanas ell #74) PAOD GS ew aa Oe ew sh See 126, 712 193 (ee ee ae ed Oe ee ON ee ee eS 1251, 510

1 Estimated.

In almost exact coincidence Maine highway traffic doubled in the three years from 1916 to 1919; it doubled again during the four years from 1919 to 1923 (this is the more significant period, since the traffic figures for 1916 and 1917 are less reliable); and the forecast anticipates that it will double again during the six years from 1924 to 1930, as shown in the following tabulation:

Total daily traffic at 26 stations

Year. Total daily traffic 191 Gls oo eae Be RR iee tes eae 7, 316 LOL OS ee ae Senn ee SOs MOON ae 2 ea. te ee ae 14, 468 LO 2 ae eee eee Pee Diese eens eee See AS RL ee 30, 569 aR She} OP epee 5 Seatins ew Be RL yin ed Pare A bee eee) Dig 1 60, 527

1 Estimated.

The Eleventh Annual Report of the Maine State Highway Commission gives a tabulation of the results of past traffic surveys, which differs somewhat in respect to the rate of increase from the figures presented above. The commission’s figures are given in the first three columns of Table 24, in the fourth column of which are given, for’ comparative purposes, the indices of total traffic at the 26 stations included in the analysis re- ported herein. It will be noted that the number of stations averaged in the commission’s analysis differed from year to year, while the analyses made in this report are based on the same 26 stations each year from 1916 to 1923, inclusive.

TaBLE 24.—Comparison of indices of traffic taken from report of Maine Highway Commission and this report | | | | Index of Average total | Number} number | Index | traflic Year | ) of vehi- | (1920= at 26 | stations | cles per 100)! | stations day | (1920= | _ *400) 2 | | we 2 xe e = =| aa 2 IRON nee SO Seen AE ps re ge oi ee) oe a ally oa 2 A 45 LOLS Se a ee SE eee a 18 428 | 83 | 55 LOLS Ss Steen: Sarin Sea aoe ees ase eps Oe 8 19 483 94 | 57 101 Geel SE a ae 4 38 504 98 88 LODO A sie eel et ee ee 41 515 100 | 100 Ope a ae ee See, ee re ee | 43 715 139 | 123 1022 a eee te ee ke en an ees 46 767 149 | 152 1025 Bee oe eee Re ee ad 49 961 187 | 186

1 Eleventh Annual Report, Maine State Highway Commission. 2 Based on 26 stations, 1916-1923.

The commission’s report states: ‘It is seen from the above figures that traffic in 1923 was two and one- fourth times as heavy on an average as in 1917. It should be borne in mind that new stations added from year to year were not located on the heaviest traveled highways. Several of these stations were off the State highway system, the object of the commission being to secure traffic data which might indicate the

location of roads which eventually should be added to the State highway system.”

Despite the difference in number of stations there is a close agreement between the indices of total traffic at the 26 stations and the indices at from 41 to 49 stations from 1920 to 1923. The number of stations from 1920 to 1923 is more nearly constant in the com- mission’s report. But the indices of traffic based on data from a number of stations varying from 18 in

286 (502 / My FORT KENT Us a VAN BUREN 4! Ye ° \ oi . catbouk / 2014 é FEN Z PRESQU | 1552 4) ue J / ‘ 10991796 ig7 4 . S a : ) . s . 4 ‘ : j r \s44 a < Ta 917 SS Say } \ : . < = gGREENVILLE 506 | {oN " AE SA TOPSFIELD a / 22 UNCOL! 733 ; } we and wi \473 over LA GRANGE SCAMS 369 d 0 i ee 606 a S } 0 \ RANGELEY Sf, 2751 X 1038 a (230 500449 oLvTowN ‘ 1752 \Y POW HEGA py 3918 733 5233 o LT) ify . fi a0 752 UPTON Be 6G Ss J \35' FARMINGTON 83q a A 2584 689 , 1369 : Z = OT FRIRFIELD =A, 1437 e eo £

‘509 fy CEIRE 4 F wateRvine NO 145 Bo b cS nd See ae Ate g

15) 5 é 15

226 3908 7 695 Oe. D>

ey Rl sf S r 0

Q 0947-7 Ve A ROCKLAND 9 5 ? a

" ‘ 83 2030 UR eT.) 32 << AUBU & fh ra 26 II | hen : BRUNSW! | 1856 yy c | SA ) |

| | | | |

, & ie PRIMARY ROAD - SOLID BLACK ow SECONDARY ROAD - OPEN SPACE

Fia. 10.—Anticipated density of traffic on primary and secondary highway systems of Maine, July to November, 1930

1917 to 49 in 1923 are misleading for prediction pur- poses. ‘The adding or dropping of stations from year to year makes the average number of vehicles per day (per station) incom parable in the given years. The ane report recognizes this defect in the note quoted above. .

The traffic forecast herein set forth is tentative. In all fairness it must be recalled that the Maine traffic records for the period 1916 to 1928 are for only one week per year, although that week is in the same part of each year. A second consideration, which is not so important in its effect upon the conclusions, is that data for 1916 and 1917 are missing at some of the sta- tions, and therefore it has been necessary to inter- polate some values for these years.

The location of the 26 stations used to measure the increase of traffic in Maine, 1916-1923, is a basis for confidence in the application of the increases there recorded to the 1924 traffic data, since the 26 stations

are widely distributed throughout the State on the routes covered by the 1924 survey. Neglecting such factors as the effect of major mechanical improvements to automobiles, it is believed that the traffic estimates here given will closely represent traffic on Maine highways in 1930.

A definite betterment of the method of planning future highway improvements is represented by Figure 10, which shows a forecast of the average daily traffic on the principal primary and secondary routes during the period July to November, 1930. The problem of caves ing such a forecast in Maine ‘was simplified by the fact that the Maine Highway Com- mission kept a record of traffic each year at a selected number of key stations from 1916 to 1924. As a number of State highway departments have had the foresight to preserve similar traffic records on their primary systems over a period of years, it should be possible to make similar forecasts of future traffic in these other States.

SUGGESTED PROGRAM OF HIGHWAY IMPROVEMENT

The forecast of expected registration and traffic is of particular importance at the present stage of highway development in Maine. The State has reached the second critical stage in its highway improvement pro- gram. ‘The first stage may be called the gravel-road stage. During this first period traffic demanded high- way service over a large mileage, and the highway com- mission wisely inaugurated the policy of stage construc- tion based on the theory of providing highway service over a large mileage rae than a concentration of ex- penditures on a limited mileage. The gravel road met this demand. ‘Traffic, however, was relatively light and, with the exception of a comparatively small mile- age of heavy-traffic routes, gravel furnished a satisfac- tory and economical surface. The proper policy was to improve a large mileage of roads to the gravel stage and confine improvements of a higher type to a compara- tively small mileage of heavy-traffic routes. The Maine Highway Commission has followed this policy in an excellent manner.

The second stage of a highway improvement program may properly be called the reconstruction and high-type improvement stage. When a State reaches this stage it is essential to set up a definite improvement policy for a period of years. Maine experience indicates that a gravel road will not carry over 500 vehicles per 12- hour day successfully unless it is surface treated.’ The average daily density of traffic on the entire primary system for the period July 1 to October 31, 1924, was over 1,000 vehicles.

Clearly, Maine is now entering the reconstruction and high-type improvement stage. The questionable economy of attempting to maintain a gravel surface on heavy-traffic routes is demonstrated by the mainte- nance costs on sections of heavy-traflic gravel roads in the State.®

The 1923 maintenance costs per mile per vehicle on the Waterville-Bangor highway are more than double such costs during 1919 and 1920. Traffic has practi- cally doubled during the same period. Similar mainte- nance costs per mile per vehicle for 1923 on the Wool- wich—Bangor highway are double the costs for the years 1918 and 1919. ‘Tables in the same report ® indicate

(Continued on page 67)

7 Eleventh Annual Report, Maine State Highway Commission, p. 17 8 Ibid., p. 15. 9 Tbid., pp. 16-17

THE WAGON AND THE ELEVATING GRADER

AN ECONOMIC STUDY OF THE WAGON—ELEVATING GRADER COMBINATION IN THREE PARTS

BY THE DIVISION OF CONTROL U. S. BUREAU OF PUBLIC ROADS Reported by J. L. Harrison, Highway Engineer

PART II.—THE INFLUENCE OF DESIGN ON ELEVATING GRADER COSTS

grader-wagon outfits and the conditions which

must obtain if a high rate of production is to be secured were discussed in Part I of this article. The proper adjustment of the size of the wagon train to the special conditions of the project in order, (1) that the number of wagons shall be sufficient to move the output of the grader as rapidly as it is produced, and (2) that their number shall not exceed the supply that can be utilized without periods of idleness by the grader, was shown to be dependent not only upon the output of the grader but Any upon the distance the excava- tion must be moved and the rate of wagon travel. The length of haul is an especially important factor in elevating grader work, and it is peculiarly affected by the design of the road.

In all grading operations rational bidding must take account of the haul as a controlling factor. This is a comparatively simple matter when the material is moved with the simpler forms of equipment, such as the wheeler and the fresno. When these implements are used cuts can generally be taken out substantially as indicated by the balance points shown on ordinary highway plans, and the actual haul will therefore be found to be closely in agreement with the calculated haul, so that a knowledge of the average calculated haul generally suffices as a general basis for estimating.

But such data are inadequate for careful bidding on elevating grader work. In the first place the transfer of the loading function to an independent apparatus intro- duces an expensive operation which, whether the haul be

ee factors influencing the production of elevating

which is an inseparable feature of the work, does have a most important bearing on the cost because of its ef- fect on the relation of the moving to the loading element, i. e., the wagons supply to the grader. It is customary for the contractor to supply a fixed number of wagons with the elevating grader. The supply furnished may be in proper relation to the grader output for the aver-

OF WHOLE CUT ENGINEER'S BALANCE LINE OF WHOLE CUT

ENGINEER'S BALANCE LINE

ENGINEER'S BALANCE LINE /

CENTER OF CENTER OF

A~- AVERAGE HAUL AS GUSTOMARILY SHOWN BY DESIGN; APPROPRIATE FOR FRESNO WORK. B- ACTUAL AVERAGE HAUL WITH ELEVATING GRADER.

Fic. 1.—Diagram illustrating difference in average haul on fresno and elevating- grader jobs age haul; but from cut to cut, and even in the same cut, the haul will often vary between limits which, if the haul is short, leave the teams idle much of the time, and if the haul is long, leave the grader idle much of the time. For this reason the average haul is not a proper basis for estimating where elevating graders are to be used.

PECULIARITIES OF HAUL ON ELEVATING GRADER JOBS

Moreover, the average haul on elevating grader work differs from the average haul as calculated for fresno

long or short, accounts for a largerpart of the total cost than the corre- sponding operation on wheeler and fresno jobs. In the second place the movement of the ma- terial in the large volumes made possible by the wagons reduces the cost of movement, so that it becomes pro- portionately less im- portant than on wheeler and fresno jobs. By reason of both of these differences the length of haul on elevating grader jobs is less important in its bearing on costs than on the wheeler or the fresno job, and _ the average haul is relative- ly less significant.

But, though thelength of haul is less significant than with other methods of operation, the fluctu- ation in haul distance,

HE generally accepted idea of the usefulness of design

is that of an instrument for letting contracts and a

guide to be followed in construction. That with a given limiting gradient and rate of curvature, and without change in the quantity of earth moved, the cost of grading with an elevating grader outfit may be varied by as much as 20 per cent, and yet the road produced in each case will be practically the same is a fact quite generally lost sight of.

Again, variation in design may bankrupt a contractor or give him a profit, although, in each case, his contract unit price may be the same and the completed road equally useful and economical in the service of highway transport.

Fluctuations in the length of haul are primarily respon- sible for high unit costs on elevating-grader projects. Within the well established limits of wagon haul it matters not so much whether the haul be relatively long or rela- tively short; but when the contractor is put to the neces- sity of moving a considerable part of the material a long distance and another considerable part a short distance, unit costs for one part or the other are likely to be exces- sive. The reason is that the adjustment of the size of wagon train to the output of the grader which is appro- priate for the long haul can not be appropriate for the short haul, yet practical considerations make difficult the changes in the size of train, which are economically necessary.

In this article the effect of length of haul is treated in detail and illustrations are presented to demonstrate the important bearing of design, involving hauls of various character, on the cost of elevating grader work.

or wheel-scraper work. With the latter form of equipment the length of haul grows as the cut and fill are extended, and the actual haul generally agrees closely with the haul distance as shown on the plans. But the elevating grader does not open cuts jas they are opened by wheelers or fresnoes. It opens the whole cut at one time, moving back and forth over such a distance as the general contour of the cut indi- cates to be desirable but always as long as possi- ble up to the full length of the cut. This gen- erates an extension of the haul distance, and the actual haul becomes the distance from the center of mass of the cut as a whole to the center of mass of the fills to

60 ‘

BP. BP.3 0 274 852 889 1004123 422 0 0 106 175 I ) 0 0 0 CY) 0|0 68 477/92 S07 SIO 763 875 765 605 S08 428 310

BP.) CuT 0 0 FILL+1S% B00 493 1060 166 0 0

pm bi T

QUANTITIES- CUBIC YARDS 100 261 «290 204 «163422

150 150 222 24 6 0

BP.4 BPS 437 2454 558316 180 0 o 28 «8646 )6«6©% 6313, S789 — 978 «B76

Q 0j7 3271272530 756 458 290 266 104 0 0 0

f SO DAYS-IOWAGON OUTFIT REQUIRED TO AV. LENGTH | HOVE 4363 YOS. FROM CUT C INTO FILLS

A |

i : , PA <— at > een tema a a

VERTICAL — FILL 2 2

AV. LENGTH OF CUT=3404 CURVE300! ie =r a

ice eh La | | Ree Lee | CENTRE OF MASS OF CUT

THIS 1M GENERAL GOVERNS ACTUAL a ——] | AVERAGE LENGTH OF HAUL

: OF CUT! —+ — sm Z | | ee | : fey les ' see aed pais Se > END :

i. r tt m= ho's

, | BASE LINE Ke digg

1 iS pF Av AV. HAUL WITH ELEVATING GRADER FOR YARDAGE IVOLVED Sj -

CUBIC YARDS

B*PLUS WAGON MANIPULATION | C*AVERAGE WAGON TRAVEL FOR YARDAGE INVOLVED |

“ty M=AVERAGE HAUL AS CUSTOMARILY SHOWN

X-Y=AVERAGE HAUL LINE |

-—5™ 1033 YDS TOTAL QUAMITY FRCH CUT'C: 4363 CU.YDS.

7 SCALE: MASS DIAGRAM-VERTICAL 1000 CU.YDS. TO THE DIVISION FEET «= ”

AT THE CUT THE WAGON LOOP WILL VARY

eA, TOTAL TIME REQUIRED 5.0 DAYS (c= 365'y | oe cee es \N LENGTH BETWEEN THESE LIMITS La 3 | HORIZONTAL 100 * eS 25 30 35 45 50 $5

40 STATIONS

Fig. 2.—Original design of sample grading project, illustrating effect of fluctuating haul distance

which material is delivered. The difference in the two cases is illustrated in the diagram, Figure 1, and in Figure 2 which is the reproduction of the center-line profile of a part of an actual project.

Between balance points 1 and 3 in Figure 2 there is a cut A, which is divided so that part of the material is hauled to each of two fills. The mass diagram which appears below the profile shows that the average haul to fill 1,as commonly calculated, is about 360 feet and to fill 2 about 110 feet.1. But in taking out material with an elevating grader cuts of this kind will not be divided as they would be for wheeler or fresno work. The grader will work back and forth over the whole length of the cut and the material will be hauled either to fill 1 or to fill 2, with the result that more or less material des- ignated by the engineer as belonging to fill 1 will be placed in fill 2 and vice versa. In a symmetrical cut the result of this practice will be to lengthen the average haul so that it becomes the distance from the center of mass of the cut (line xy as shown on the mass diagram) to the center of mass of the fill. In this way the average haul to fill 1 israised from 360 to about 400 feet and the average haul to fill 2 from 110 to about 250 feet. A study of the other cuts in Figure 2 shows the same tendency toward an increase in haul distance in all except cut D, all of which is hauled to one fill. Where this occurs no extra haul is generated by the use of the grader.

The result of increasing the haul to the center of mass of the cut as a whole in cut A is more marked in its effect on the haul to fill 2 than to fill 1. This is gen- erally the result where the quantity to be moved in one direction is considerably larger than the quantity to be moved in the other. The haul determined in this way, however, may not be exact. Thus, if cut A had been so nonsymmetrical that the depth of excavation between stations 27 and 29 had considerably exceeded the depth of excavation between stations 25 and 27, the grader might be operated here on a short loop until the material remaining to be taken out was reasonably symmetrical over the whole cut. If this were done the material for fill 2 would be secured with a somewhat shorter haul than the method of calculation described above would indicate.

Similarly, the manner in which even a symmetrical cut is taken out may somewhat affect the length of haul. Thus, if instead of taking a first cut along line ab it is taken along line cd, the haul may be somewhat

1 There are a number of methods of calculating haul. The one here used, which is the simplest and quite accurate enough for the purpose, assumes that the average haul is the distance between the points halfway from the base to the peak of the mass curve on the cut and fill slopes.

affected. But in operating elevating graders the general practice is to make the runs as long as possible. and for this reason if the cut is anything like aya cal the tendency is to make the average haul the dis- tance from the center of mass of the cut to the center of mass of each of the fills or fractional parts of fills into which the cuttings are placed. This should there- fore be used as the basis from which to calculate haul. But it should be recognized as an approximate rather than an exact basis, as special conditions of the sort mentioned will often enter to make the actual results somewhat different from the theoretical. Lack of symmetry in the cut is responsible for most of these special considerations. It creates short grader runs, unproductive runs, nonuniform bite, etc., none of which need affect the haul distance as theoretically de- rived, but all of which do, more or less, because, under field conditions, there generally is less thought given to these matters than isneeded tosecure accurate results.

EFFECT OF LAYER DUMPING AND WAGON MANIPULATION ON HAUL

Layer dumping also tends to affect haul. If it is required, as it should be, there is a tendency to increase haul at the fill. Thus, in Figure 2, it may be assumed that instead of placing fill 2 as shown on the plans the material secured from cut A is placed in two layers which extend well beyond balance point 3. In such a case the actual average haul instead of being 250 feet might easily reach 300 feet. There is no way of cal- culating such extensions in advance. They are rather to be considered as an element likely to create excess haul and therefore one which a contractor should watch and avoid. It is not at all necessary that layer dumping cause any considerable amount of extra haul.

Besides these conditions which affect haul there is another arising from the manipulation of the wagons themselves. The general operation of the wagon train, somewhat distorted for the purpose of illustra- tion, is shown in Figure 3. As the elevating grader is moved toward the dump the empty wagon must return to a point some distance back of the loadin wagon in order to reach position. Let it be assume that wagon 10 is loading along ab and wagon 11 is the replacement wagon. Let it also be assumed that the average distance required for picking up a load is 75 feet. The distance that the load as a whole must be hauled will, of course, be calculated from the center of the distance over which the load is picked up. There is then a necessary addition of 374 feet to the average distance over which the wagon will be moved which addition covers the distance traveled by the

QUANTITI

BP.6 954 483339728 335 202 150 W2 157 S26 1068 1252 896 283 46 0

0 QO

ES-CUBIC YARDS B.P.7

oom BPS

BPS NS $02 750 750 2200 489 315 % 178 130 100 O 0 0 0 0 0

W2 1090

eae eens 2-5 0 O- 0 “0 150 “805

1S72 657 \281 7I2

HE 2 0/0 0 0 64h 32% 353 303 337 564 635 762 770 888 236

ee —_ ee et | Pee all le | AAV. LENGTH OF CUT» 150° L—" 5 + + + + SS a a el Se SS p— I i |g. VERTICAL CURVE:400' J preter eal | MAX.CUT NEARLY 700! c AV. CUT ABOUT Sso’__| THOD B f T END OF JLLUSTRATI PROFILE +++ Attar — pur nor THE End oF | 4.900 x fate b+ / 18 = 80 THE PROJECT ——+} A= 580° | esi b C=7 | , B= ah } = = = 43,000 2.000 | RNAL BALANCE at; | 251 CU.YDS. * ae 42000 © iat ia, : = : i AS pena tl S20 ie. L - 1.000 2 = Lovaas ase une | _/| | 2 Z| METHOD B 8 pec METHOD A & 3 : Be Nee | : weT0s6 i Foca ae ¢ +180 -—} —}—MASS-| — ins Ween engine cs a Ce r -|— DIAGRAM —— faut’ = Sango ss 11.000 2000. reall ail 4 ; Kies C* 440' y CASTED= 2256 » » 60 65 70 75 80 6s 30 2,000 STATIONS Fic. 2.—(Continued)

wagon before the beginning of the average haul dis- tance for the total load is reached. To this must be added whatever distance was traveled after wagon 11 fell in behind wagon 10 in order to be in a position for prompt replacement [ven if the wagon train is in close harmony with the output of the grader, there must still be a short distance allowed for this purpose, say from 10 to 15 feet. If the haul is to fills on both sides of the cut, this extra distance will generally be avoided; but prevailing practice is against taking out cuts in this way, because it doubles the force employed on thedumps. With wagons moving toward the dump, therefore, there is then an excess of wagon travel over iS average haul, for the load as a whole, of about 50 eet.

A similar situation prevails when the grader is mov- ing away from the dump. In this case each wagon must move an average of 3714 feet beyond the average haul for the load in order to secure its full load. Moreover, in driving to a clearance for the replacement wagon the loaded wagon must move ahead far enough to permit the replacement wagon to reach the loading position before a turn is made. This will require at least 15 feet and often more. Whether the grader is moving to or from the dump, therefore, the wagons actually travel about 50 feet further than the average haul for the load, the additional travel bemg necessary in the interest of manipulating the wagons at the grader. Applied to the cut which has been used as an illustra- tion, this results in an average wagon travel of 450 feet to fill 1 and 300 feet to fill 2, with the possibility that when layer dumping is required the haul to fills as short as fill 2 will be somewhat further increased.

WORKING THE WHOLE CUT etn arts ADVISABLE DESPITE LONGER AUL

Ordinarily the contractor will not find it to his interest to avoid the extra wagon travel that arises from the failure to follow the engineer’s balance points. With normal efficiency in the operation of the grader and an adequate wagon supply, a cut such as A, which averages about 340 feet in length, permits of working the grader about 50 per cent of the time, but if such a cut were divided into two parts and taken out in accordance with the engineer’s balance points the shortened run would permit the grader to work only about 34 per cent of the time in the shorter cut. The resulting loss in output would generally outweigh any advantage that might be obtained from the shortened haul, since it is probable that the wagon time saved by

reducing the haul would be wasted in waiting for loads, for it must be remembered that the wagon train gen- erally consists of a fixed number of wagons; therefore, unless ‘the grader output is correspondingly increased, shortening the haul merely tends to cause a piling of the wagons. This is invariably the result when the haul is within the capacity of the wagon train. If the haul is beyond the capacity of the tram, the reduction in haul by splitting the cut may overbalance the reduc- tion in grader output, but cases of this sort are com- paratively rare, and to take advantage of them the contractor must have at his disposal the accurate data supplied by the mass diagram.

AVERAGE OUTPUT 1,000 CUBIC YARDS A DAY

An analysis of the average wagon travel when com- bined with an analysis of the average length of each cut, by which the possible output of the grader is indi- cated, will serve to avoid many of the speculative risks contractors encounter in elevating grader work. To be really effective, however, the analysis should be extended to include a study of the haul cut by cut, and

HAUL FOR WAGON 10 HAUL FOR WAGON I!

PATH OF LOADED WAGONS — \\ a rmorrerumucmens |)

PATH OF LOADED WAGONS — Vee ota ncde)

5) Snes Mies Ses FOR WAGON 10 -

HAUL FOR WAGON I!

Fic. 3.—Operation of wagon train on each side of grader loop

the results of this analysis developed on the basis of some standard unit of production. For this purpose, in the description of ae method which follows, an output of 1,000 cubic yards per day has been used. he bureau’s studies of elevating grader projects indicate that the average length of cut is about 450 feet. The studies also mdicate that, when the wagon supply is adequate, ordinarily eflicient operation results in an exchange of wagons in about 11 seconds. The time required to load a wagon averages about 23 seconds. With due allowance for breakdowns, clean outs, rests, etc., these conditions permit of securing

BP. oO

BPI BP2 cuT 0 0 320 1/80 ISI9 41 1960 920 O

QUANTITIES~ CUBIC YARDS 3

BP4 BP. 240 250 16) 113 256 1045 142171 850 18 0 O

0) 1G0ee2O5a ca One OlnO Om Om SI 0. 0 43 70 258 430 410 310 FILL+15% 300493 1060 166 0 O[0 0 O 138 [21 184 490 69 753 727 182408 437 320 168 146 241 297 153 0 OJ0 70 4525S 756 458 319 310 84 0 0 0 i cu A |oox uate CuRVeZsg rT Ae x re) CURVE= 5 . 0 1 H ! alle _ 2 Son !.9.% |CURVE'SO | 9.0% meee | + aVERAGE LENGTH OF CUT» 200FT-

~ VERTICAL CURVE*S0

7 O ERTICAL ed ey

CURVE: 150) TAV. LENGTH OF CUT= 375'~

| Sis

CUBIC YARDS

A= AVERAGE HAUL WITH ELEVATING GRADER FOR YARDAGE |

B= PLUS WAGON MANIPULATION +} [ t

= AVERAGE HAUL LINE |_| i aac

— C= 875'+—_+ MASS ~ + DIAGRAM i

pers

SCALE-

_| MASS DIAGRAM-VERTICAL 1000 CU.YARDS TO THE DIVISION i

+ | PROFILE “ LOMIMEEETION: (aienlia HORIZONTAL |100 “

30 3s

Fia, 4, the cuts.

an output somewhat over 100 cubic yards an hour with only average efficiency in operation. Allowing, then, for the losses in working time which, on practically all jobs, result in reducing the working day to some- thing under 10 hours, it is still possible for the average contractor, with no change in managerial policies and no improvement in general efficiency, to secure an output of 1,000 yards a day if his ee supply is adequate and his cuts are of standard length. ‘This output has therefore been used as a basis from which to work in showing how the length of cut and the length of haul are likely to affect output and why contractors often lose money on work of this character through a failure properly to gauge the effect of those elements.

CORRECT BIDDING IMPOSSIBLE WITHOUT STUDY OF HAUL

It will be seen, in cuts A and B, Figure 2, that a knowledge of the average wagon travel does not cover the situation. Thus cut A can be taken out with an average wagon travel of 450 feet for the material moved to fill1. The mass diagram shows that there are approxi- mately 3,000 cubic yards of material to be awe into this fill. But of this amount 1,000 cubic yards calls for an average wagon haul of about 520 feet, 1,000 cubic yards an average haul of about 450 feet, and 1,000 cubic yards an average haul of 365 feet. In comparison with this the mass diagram for cut B shows about 5,000 cubic yards of material to be placed in fill 3. Of this material 1,000 cubic yards must be moved 1,470 feet, the second 1,000 cubic yards 1,290 feet, the third 1,000 cubic yards 1,180 feet, the fourth 1,040 feet, and the fifth 1,000 cubic yards 860 feet. What is perhaps the most serious problem the con- tractor has to meet in this sort of work is brought out clearly by the study of these two cuts. An output of 1,000 cubic yards has been set up as the standard day’s work, assuming normal efficiency. But if the eight standard days’ work in these two cuts are sabeeal it will be apparent that the work can not be performed in eight days with any ordinarily constituted outfit, be- cause the range in haul distance is too great. Such a tabulation, in which the effect of length of cut has been purposely omitted, is shown in Table 1.

Table 1 illustrates clearly the dependence of produc- tion on the proper adjustment of the wagon train to the length of haul and the danger of depending on the aver- age wagon travel in analyzing elevating grader projects.

First re-design of sample grading project, illustrating the possibility of equalizing haul distances. This assumption limits the reduction of haul to about half the distance center to center of cuts

40 STATIONS

45 so

In this design it is assumed that fills will be built entirely from

TaBLE 1—Effect of length of wagon haul on elevating grader production and time required for grading

(Based on cuts A and B, Figure 2)

= Num- | Using 8-wagon Time | ber of outfit re- | wagons}. 22 Spe | Ce Equiv- Material moved ere Wagon quired able fe alent foal terial | 22Ul | for full | Team | Grader pany each vate output | time | time D 1,000 8 ' of | wasted | wasted | cubic | grader yards “| je = Cubic Per Per Cubic | Cubic yards Feet cent cent yards | Days yards | ee ees 1, 000 520 | 8 0.0 0.0 1, 000 | 1.0 1, 000 ce one 2 SS er 1, 000 450 | 7 1255) 0.0 | 1,000 1.0 1, 000 [at a 1, 000 365 | 6| 25.0 0.0 | 1,000 1.0} 1,000 Oo tee se sae) 000 1,470 | Hata es ee 50. 0 500 | 2.0 2, 000 BIS ENS cf ce me 1, 000 1, 290 | Lbs 47.0 530 | 1.9 1, 887 On) eee see 1, 000 1, 180 13 eee se oes 38. 0 620 | 1.6 1, 613 breed, Lame eee 8 1, 000 1, 040 1 2 ees eee 33. 0 670 1.5 1, 500 Ca eee | 1,000 860 10 se a oe ae 20. 0 800 1.2 1, 250

1 Based on standard daily production of 1,000 cubie yards.

Time required for movement of 8,000 cubic yards, 11.2 days; probable average out- put per day with 8-wagon outfit, 720 cubic yards.

Cuts A and B are on one project and only a short dis- tance apart. The average wagon travel from cut A to fill 1 is 450 feet, and from cut B to fill 3 it is 1,180 feet. These averages would indicate that trains of 7 and 138 wagons, respectively, would be required for 100 per cent production at the grader as against the range of from 6 to 16 wagons shown by the detailed analysis actually to be required if full production is to be se-

cured. If an 8-wagon outfit were used, 100 per cent orader ee could be obtained in cut A, but the longer hauls of cut B would reduce the average daily

output for both cuts by 28 per cent. Even if the long wagon train indicated by the average travel to fill 3 were provided, full production at the grader still could not be Senna at all times. The point to be stressed here is that haul varies over such a wide range that no contractor is in a position to make other than a random guess as to what the work on any project will cost without a careful analysis of this element.

THE MASS DIAGRAM AS A MEANS OF CONTROLLING FIELD

OPERATIONS The analysis of elevating grader work through study of the mass diagram can be made an effective means of controlling field operations. Thus, cut E is a sym- metrical cut from which approximately 6,000 cubic yards of material are secured. Wagon haul per 1,000

QUANTITIES ~CUBIC YARDS BP.8

0 00 0 150 805 1112 N00 18541 930 712 366 25

B.P.6 BP7 31039 96234 320 187_— (120,95 660155 535 1120 1320 896 283 46 O

Meaty oe 45 224 303 263 510 0 0O 0 0 AVERAGE LENGTH OF CUT=350° ail |

STATIONS

BPS BP 7 WS S02 1470 34017801347 270 «25763 0 0 O0jJ0 0

Wal They Wx Las eer wea

CASTED* 2462

| | — ze | oc | ee a ' 1 i] a ah hea LENGTH OF CUT®* 300 FT. }—_;—_+— + | | | | | | | 142.00° ie OVERTICAL OFS VERTICAL

ee adi ~—}~ CURVE#210' 7 |

___END OF ILLUSTRATION BUT NOT THE END OF | THE PROJECT ————}

Ses CURVES (10a ent ;

——J 0.0%

a ier ir | he PROFILE | ocstekeneh |

T | |

SGUVA 918N9

Fic. 4.—(Continued)

cubic-yard unit to fill 8 varies from 435 to 1,175 feet. But this cut offers a grader loop varying in average length from 150 feet for the top three feet to over 420 feet at the bottom. At the top the grader loop will be short and the production low. If the top of this cut is placed at the far end of the fill, the low output at the grader and the long haul tend to offset each other, with the result that only 12 wagons will be required in order to maintain an adequate supply at the grader. If thisis done, the bottom of the cut will fall at the near end of the fill, and for placing it here 7 wagons will be required. If this process is reversed, the aly of the cut being placed at the near end of the fill, only 6 wagons can be used, while in placing the ma- terial from the bottom of the cut at the far end of the fill 16 wagons could be utilized. If the wagon train consists of, say, 10 wagons, 30 per cent of the wagon time would be lost in inet the close-in material, and the grader would be idle about 17 per cent of the time in placing material at the far end of the fill under the first scheme of operation. If the second scheme of operation were adopted, 40 per cent of the wagons would be idle while the material close in was being placed, and the grader would be idle about 37 per cent of the time while material was being placed at the far end of the fill. The advantage of the first arrangement is clear. ‘There is no way of determining

oints of this kind by rule of thumb. Therefore the field superintendent often overlooks them. They are clear enough, however, when the mass diagram and the profile are thoughtfully scrutinized.

This is only one of the many illustrations which could be given to show that the mass diagram on work of this kind offers a logical means of controlling field operations, just as it offers the proper basis on which to study a project prior to selecting the outfit best suited to economical work on it. Another illustration of the usefulness of the mass diagram in controlling elevating grader work is found in fills 6 and 6a (Fig. 2), which are built from cuts C and D. In this case the mass diagram indicates the movement of approximately 5,300 Rabie ards of material between balance points 6 and 7. ‘There is a considerable excess of material— about 1,200 cubic yards—originating in cut C which must be hauled to some point beyond cut D. ‘There are approximately 250 cubic yards in a small fill between cuts C and D, which for the purpose in hand is of no consequence, and some 4,100 cubic yards originating in cut D which must be placed in fill 6a. The mass

diagram indicates an average haul of 480 feet for this latter material. If to this is added 50 feet for wagon manipulation, the average wagon travel becomes 530 feet. As against this the average wagon travel for the 1,178 cubic yards originating in cut C is 1,760 feet, if this material is hauled to the far end of fill 6a. If, however, this material is placed at the near end of fill 6a the wagon haul is reduced to 1,420 feet, and by so doing the average wagon travel on the material taken from cut D is extended to 630 feet. This illustration shows that contractors can often improve output by studies of the details of the work. At current bid prices on this sort of work (about 25 cents per cubic yard) the gain in daily production with a 10-wagon outfit would be worth nearly $16, as shown by Table 2, which is a saving well eet while.

TABLE 2.—Comparison of production under two methods of working cuts C and D (Fig. 2) with a 10-wagon outfit (average management)

| | Scheme A Scheme B | od Naty pots. Tae Wagons Days Wagons! Days Material | Quan- Te- Pro- | work re- | Pro- | work from cut tity quired |duction| re- | quired duction) re- Haul | for 100 | with | quired | Haul} for 100 | with | quired percent; 10 percent) 10 | pro- | wagons pro- | wagons duction | duction he SEAR ae oe ee = Cubic Per jeer yards | Feet |Number| cent |Number| Feet Number cent | Number (Gye ae 1,178 |1, 760 23 44 2.7 |1,410 1 3 | 2 1B ere ae 822 | 660 9 100 0.8 | 755 | 10 | 100 0.8 A is ere 1,000 | 600 9 100 1.0 | 685 | 9 100 | 1.0 Dasa a Rere aa 1,000 | 500 8 100 1.0 | 620 9 100 1.0 ‘LA ee Be se 1,000 | 415 df 100 TRON) 625 8 | 100 | 1.0 10 Pr ne, 350 325 6 | 100 | 0.3 | 470 | a 100 0.3 AL OGelillet5; 360)g ease seen ee See lea GRSO 124 set yea Jaen = ee, | 6.3 | | Average daily production: Cubie yards Schomé Bi 225 Sp lie 2 eee ne See Se oes ee ek 850 SGherne Ae eee kes eee eee ees een ee ee ee Pe 787 (Cy Ghose, ee, hee See Ce ae See, Eee ees he a 63

At 25 cents per cubic yard, value of increased daily output—#3 X.25=$15.75.

A wide-awake superintendent can sometimes save team time by using a double dump. This is of ad- vantage only when a fill contains yardage that is within the haul limit of his outfit and other yardage that is outside of this limit. A 10-team outfit, with average management, can keep the grader busy up to a wagon- travel distance varying from 600 to 850 feet, depending on the length of cut from which the loads are being secured. As an illustration, suppose the mass diagram

64.

QUANTITIES - CUBIC YARDS

BPS BP6

BPI BR2 BR3 B.P4 Ae : BR7 oe CUT 0.0 O 202 880 1100809664535 O 152 200 22 00 O te) 0 ie} 91 240 250 16! 536024115 1045 2185 850 18 0 0 00 43 70 248 347 ISI 114

FILL+15% 300493 1060 138.0 0 010 24 324 187 173 490 ai56 753 727590 4373201168 146 241 491481530. 0 O 70 454 2530 756300158 313 310 84 0 0]0 > CUT A | [cul C7 i Mas Als | VERTICAL + } ; 4 + =200' | so] VERTICAL VERTICAL AVERAGE LENGTH OF CUT= 200 oe 50.00% Ts. | 299g RYO CURVE=250._ 7 VERTICAL | *2-q7% | CURVE:250 oot aay son ee 0.0% 5 ze } VERTICAL—> t CURVE*250 40% 5 288 VERTICAL | VERTICAL Ney) 9 EL 27 Fines] CURVE:250/ 8 0.00%| | CURVE:150 CURVE=100' JA see al a en Ie | MI 7 SH la= 260 NGTH OF CUT 350° | oe ot ~ Bx 80 SCALE- 2000 Ruiiee aN e 7 — PROFILE Ay c= 310 | MASS DIAGRAM-VERTICAL 1000 CU. YDS A=560 SAF 3a | B= 50’ A TO THE DIVISION. 1000 me: Z C610 '~BORROW.——— 3052 CU.YDS. | PROFILE-VERTICAL 10 FEET 10 THE 3000 w | b ee SSE aoe e (HORIZONTAL 100 FEET. TO THE | AVERAGE HAUL 400 x = 00 ee + DIVISION. 2000 Ss — |NTERNAL BALANCE —>1 1000 a 1000 THORAC Uae =400' = A= AVERAGE HAUL WITH ELEVATING GRADER See ey CTRL ae le ae NG ceace FOR YARDAGE INVOLVED of eS Ld og 2000 Sie] —} PLUS WAGON MANIPULATION = y es a ee aes ae 330] _ CTNERAGE WAGON TRAVEL FOR YARDAGE INVOLVED = a 3000 te A® 330, | X-y= AVERAGE HAUL LINE — 4—MASS | DIAGRAM ] A= 370. 1000 = _50 B= 50' | Y | C= 380 | |. | OBS 2000 25 30 35 40 45 50 55

STATIONS

Fic.¥5.—Second re-design of sample grading project, illustrating how hauls may be further reduced by use of borrow pits

indicates that the current day’s work involves an average wagon travel of 350 feet. Six wagons are re- quired to keep the grader busy, and if eight are sent out the time of two will be wasted. If under such con- ditions enough wagons are diverted to a longer haul, so that the proper rate of wagon supply is maintained, the time of the two wagons can be saved. <A study of the time-distance graph for wagons (the time-distance graph will be discussed in the third part of this article) will show how many wagons must be diverted if this method of operation is to be successful. When this is done, however, the superintendent must use consider- able care to insure that the long-haul wagons do not become bunched, as bunching will largely obliterate the benefit to be derived. The dumping at the long-haul dump need not be given much supervision as it may be so handled that subsequent operations will cover work of this kind and correct any careless placement of material.

The mass diagram may also be made to give a picture of each day’s work and so to assist the contractor by showing how much material hehasplaced. How thiscan be done is shown in the mass diagram for fill 5 (Fig. 2). Once the mass diagram is in hand all that the contractor needs to know is the distance completed in order to determine the yardage he has placed with considerable accuracy. This is a valuable control and one that should not be overlooked.

POOR DESIGN REDUCES ELEVATING GRADER OUTPUT

The foregoing illustrations indicate some of the prob- lems a contractor faces in his effort to operate an ele- vating grader outfit with maximum efficiency. They show that the mass diagram is a valuable guide to sroper bidding and also in the conduct of the work.

ut they also show clearly that the highest degree of economy may be impossible unless the road is designed with that end in view. The profile shown in Figure 2 represents a decidedly poor design for elevating grader construction. The essence of economical design for this type of equipment is that the cuts and fills shall be so related in yardage and in the distance between them that a reasonable wagon train can keep the elevating grader operating at or near full capacity all the time. This means that variations in haul should be kept within a reasonable range. A design which produces a succession of long and short hauls, such as are found in fills 1, 2, 3, and 4 of Figure 2, violates the first prin- ciple of economical elevating grader operation: First,

because the short cuts reduce the rate of output of the grader; second, because some of the hauls are so lon

that no reasonable wagon train can handle the ful output of the grader; and third, because other hauls are so short that the wagon train can work but a frac- tion of the time with the grader working at full speed. More nearly correct treatments of this section of high- way are illustrated in the redesigns shown in Figures 4 and 5.

In preparing these modified designs it has been as- sumed that local conditions govern the height of the fills. These have, therefore, been left approximately at the same height as in the original design, and the modification in the grade line has been limited to a readjustment of the cuts in order to secure more nearly uniform hauls. Cut depths have been freely altered and vertical curves have been standardized by the adoption of a uniform radius of curvature of approxi- mately 5,000 feet. No particular effort has been made to keep the yardage the same as in the original design, although it is approximately the same. The purpose is to illustrate certain principles of design, the employment of which is not in any way dependent upon the yardage.

The object in presenting the redesign shown in Figure 4 is to lay emphasis on the manner in which by careful design the haul on elevating grader projects can be so adjusted as to improve output and reduce production cost. In this first redesign it has been as- sumed that the fills will be built entirely from the cuts. Obviously this assumption limits the reduction of the maximum haul to about half the distance from center to center of cuts, yet even with this limitation it is possible materially to reduce the wagon travel. Under the original design only 42 per cent of the material could be moved with a wagon travel of less than 600 feet, and 35 per cent involved a travel of over 900 feet. Under the first redesign (Fig. 4) 59 per cent of the ma- terial can be handled with a wagon travel of less than 600 feet and only 8 per cent requires a travel of over 900 feet. The haul of this latter material is imposed by the distance between cuts, and as already stated it can not be reduced under the system of design in use.

PRODUCTION COST REDUCED 11 PER CENT BY FIRST REDESIGN

That the first redesign is an improvement from the standpoint of the contractor will be apparent without much explanation. Under the redesign economical operation requires nearly as many wagons as under the

B.P.10 All 161 S89 156 WTS 900 382 69 ep 6 9: '¢

ies

- 1 AVERAGE LENGTH OF CUT#=350 —

0 63 (21

398

128 297

DIAGRAM

STATIONS

Fic. 5.—(Continued)

original design, but because much less work has to be done over the long wagon travel distances the cost of production is reduced about 11 per cent. At the pre- vailing bid price for work of this kind (25 cents per cubic yard) this difference, if obtainable on projects generally, should in the long run mean a reduction of from 2 to 214 cents per cubic yard in the price paid by the State for elevating grader work. Whether on any large percentage of projects a similar saving could be made by redesign has not been fully investigated. This is, however, of less importance to the designer than the fact that it can be made on some projects.

To the contractor such a saving is of vital concern for his money is at stake. To him the original design and the redesign present a concrete example of how design often affects his profit by introducing a wide range of wagon travel; and the comparison of the two designs should explain why two jobs in which topographic conditions are similar may return dif- ferent percentages of profit or loss. The writer has more than once been told by distracted con- tractors that it has been impossible to obtain proper production on the job in hand though jobs in similar territory had on other occasions yielded a fair profit; but never has there appeared to be any appreciation of the fact that the fault might le in the design rather than in the way in which the job had been handled or that the size of the outfit might have affected the cost of handling the work.

BORROW PITS REDUCE COST BY ELIMINATING LONGER HAULS

Figure 5 shows a second redesign. Under this design long haul has been further reduced by the use of borrow pits. In the Mississippi Valley it 1s often possible to obtain stripping rights, i. e., the right to take material to a certain depth, generally a foot or two, from abut- ting property. The advantage of this practice hes in the fact that the grader run can readily be made such as to yield 100 per cent production at the grader, while at the same time the haul can be kept within the ca- pacity of a normal wagon train.

Whether to use the method or not, from the stand- point of the State, depends on the saving likely to result and the cost of the rights. From the standpoint of the contractor its desirability is apparent as its use reduces the longer hauls imposed in the first redesign by the distance between cuts. Under this design only seven wagons would be required for the most economical

prosecution of the work, 87 per cent of the material would be hauled less than 600 feet, no material would require wagon travel in excess of 900 feet, and the pro- duction cost would be 20 per cent less than under the original design. A condensed comparison of the three designs is given in Table 3; the methods used in deriving the results shown will be explained in Part 3 of this series of articles.

TABLE 38.—Compdrison of cost of three designs using various wagon trains

First redesign} 29,887 | 14.1 | | \ |

1 Based on standard daily production of 1,000 cubic yards.

Minimum production cost: Original design, 15.8 cents with 11 wagons. First redesign, 14.1 cents with 9 wagons. Second redesign, 12.7 cents with 7 wagons. Difference in production cost=8.1 cents, or about 20 per cent.

PRODUCTION COST IN RELATION TO HAUL

The relation of haul to cost may be further illus- trated by a very general production cost statement. Under the wage scales prevailing in the Mississippi Valley and contiguous territory the fixed costs of operating an elevating grader are not far from $80 a

day. The cost of hauling is about $5 per team per day. These costs cover field pay roll, feed for the

teams, cookhouse losses, and minor repairs only and, for the purposes in hand, will be referred to as the production cost. The contractor has many other

costs to meet, such as the costs of office overhead, bond, financing, getting onto the job, depreciation, ete., all of which are presumably included in the bid price, but these are largely BES of production cost and should not be include

factors affecting production cost that are under con- sideration.

Accepting the above production costs as a basis of comparison and assuming the condition of an elevat- ing grader working in a 450-foot cut and the wagon supply menue for standard production of 1,000 cubic yards a day at the various lengths of wagon travel, the costs of production per cubic yard will be as shown in Table 4.

TasLte 4.—Unit costs of production for standard production from a 450-foot cut with various hauls

: = | Daily

| | iets Feet | Number | Dollars Cents | 825 6 | 110 500 | 8 120 12 675 10 130 13 850 12 140 14 | 1, 025 14 150 | 15

Average rate of increase, 0.6 cent per station.

The table presents, of course, a highly generalized statement of the costs, but it will serve to show, for example, that if the wagon travel can be kept down to a point where an 8-wagon outfit can be appropri- ately used, production cost will be about a cent a yard less (bid prices should average about 2 cents less) than where the wagon travel is such that a 10- wagon outfit is required. If, with any given wagon supply, the length of cut is shortened the effect will be to lower production so that the saving resulting from a shortening of the haul may in this way be offset by the reduced output obtainable.

If, on the other hand, the wagon supply is not adequate, the cost will mount rapidly. Thus, if an 8-wagon outfit (basic cost of production 12 cents) is working where the wagon travel is 1,025 feet, it will supply only eight-fourteenths of the necessary num- ber of wagons; the production will fall, therefore, to eight-fourteenths of normal, and the cost of produc- tion will rise to 21 cents.

Two important points should be somewhat clarified by this analysis. The first of these is that the con- tractor who undertakes a project with less than the proper wagon supply will generally find that bis produc- tion cost is higher than the haul distances prevailing would normally generate; and the second, that the injection of occasional long hauls has relatively a more important effect on production cost than a general increase in the haul for which provision can be made in the selecting of the outfit.

To the contractor this latter point is of special importance in that it shows that bids on overhaul must be carefully scrutinized. It is customary to take overhaul on work of this sort at about 2 cents per station yard. If the station yardage of overhaul is large, the contractor will be justified in providing a wagon supply sufficient to care for it properly, and the price of 2 cents may be sufficient or even excessive, but more often the overhaul is generated by a few cuts from which long hauls are required. In such cases it is not practicable to increase the wagon supply and

, since it is only the:

the output may be so reduced, when operating on this long-haul work, that the production cost alone may about equal the price received. In such cases the contractor loses on his overhaul.

SUPPLEMENTARY USE OF FRESNO MAY SAVE MONEY

In the foregoing discussion it has been assumed that contractors use an outfit of fixed size. This, in fact, is the all-but-universal practice. Under this system team time is lost in considerable amounts whenever the wagon travel is short, and grader time is lost whenever a long travel distance is encountered. There is, however, another method of handling such work that deserves more consideration than it 1s now receiving.

It is well known that the fresno can move [dirt on short-haul jobs about as cheaply as it can be moved by an elevating grader outfit. This being the case, there seems to be no good reason why the fresno and the elevating grader can not be combined with profit when the conditions warrant. There are a good many angles to this question, and it is quite impossible to treat all of them in the short space here available. Briefly, however, the situation is substantially this: The ele- vating grader is a wonderfully effective loading mech- anism; the wagon is perhaps the most efficient haulin mechanism available for work within its proper field. As long as these can be kept in balance and efficiently operated, the cost of producing yardage in place is probably as low as it can be made with any type of earth-moving equipment, particularly if the haul is of any considerable length. However, as the haul ap- proaches zero there is a short distance, probably not exceeding 200 feet, in which the fresno can produce yardage in place about as cheaply as the elevating grader. For such short hauls the wagon supply of the elevating grader must be excessive, since it is properly designed for the longer hauls. On the average project there is always a certain amount of work to do which is well within the field of the fresno, and there are hauls which, while clearly within the field of the elevating grader, are shorter than the average for the project and are capable of handling with less than the full outfit of teams. If, whenever this condition obtains, the teams not needed by the grader are shifted to fresnoes, whatever yardage is moved by the latter will represent a clear gain in production.

The field of competition again turns against the fresno when the distance becomes so short that the elevating grader can cast the material into place, as- suming, of course, that no wagons are kept ie during the casting operation and that the ditches are not so deep that the output of the grader will be sharply reduced by the tilting of the machine. But the fact that is apt to be overlooked in considering the relative cost of short haul and casting is that so long as the contractor must maintain his teams (including drivers) he can gain nothing by casting unless he thereby in- creases his output per hour. The possibility of increas- ing output by casting lies in the fact that the time lost in wagon exchange is saved, but this saving is not always a net gain, because a certain amount of time must always be lost in resting the grader stock. Asa matter of fact, when the grader is drawn by a tractor or by 20 horses the output generally is somewhat in- creased when casting, but if only 16 horses are used the aggregate of the rest periods is generally about as great as the time lost in wagon exchange, and no par- ticular advantage accrues.

Under these general conditions if a contractor, de- siring a high average rate of output at the lowest ossible cost, instead of selecting a wagon train on the asis of the average haul would select it on the basis of the longer hauls and then plan to send out with the wagons each day only those teams which can be worked to Papacity, using the balance in taking out ditches and short-haul cuts with fresnoes, he would find that under practically all circumstances his grader could be worked to pee and his extra teams, instead of spending much of the time waiting to be loaded, would be producing yardage ata profitable margin. In discuss- ing this scheme of operation with contractors two objec- tions to it have been raised: First, that teamsters operat- ing wagons do not like to transfer to fresnoes and, sec- ond, that the standard 14-yard wagon requires only two horses while the 4-foot fresno requires three. There is a valid answer to both objections. To the first there is the answer that employers generally find no difficulty in enforcing conditions which are clearly set forth when men are employed. The other may be met with the blunt statement that the 14-yard wagon has no ees on elevating grader work and should be replaced by the more efficient 2-yard wagon. The 2-yard wagon requires three horses, but day in and day out it will haul 50 per cent more than the 114- yard wagon. Where it is used there will be no diffi- culty in shifting the 3-horse teams to 4-foot fresnoes.

TWO-YARD VERSUS ONE AND ONE-HALF YARD WAGONS

The desirability of using 2-yard instead of 114-yard wagons needs no very extended defense. In the first place, as noted above, 50 per cent more yardage is secured per load at the expense of only one extra horse. At the present time it costs about 70 cents each per day to maintain stock. With drivers at $3.50 the cost to a contractor of maintaining a 2-horse team on the job is in the neighborhood of $4.90 a day. As compared with this, the cost of maintaining a 3-horse team is about $5.60. Thus, with a 14 per cent increase in cost a 50 per cent larger load can be moved, and this is an advantage that no contractor can afford to overlook. Moreover, the actual load per horse is slightly less when three horses are used on a 2-yard wagon than when two horses are used on a 14-yard wagon, because while the pay load per horse is about the same, there is no important difference in the internal frictional resistance of the two sizes of wagons.

In addition to this saving in the hauling cost, which is a relatively large one, the larger normal grader output must also be considered. This larger output is due to the smaller number of wagon-exchange periods for a given yardage. As by its use only about two-thirds as many waits between loads are required, the 2-yard wagon, used with normal efficiency should produce at least 10 per cent more output than the 14-yard wagon.

The one valid objection which has been raised to the use of the larger wagon is that in soft ground it tends to mire down a little more than the 14-yard wagon. This can be avoided by supplying the larger wagon with a tire of proper width.

It is impossible to recommend the use of wagons larger than the 2-yard size, because when more than three horses are used there is difficulty in getting under the belt quickly. There is also some difficulty in maneuvering at the dump. These problems are not, however, of any consequence where three horses are used, and the evident success of those outfits now using 2-yard wagons offers concrete evidence that the advantages here noted are being secured by at least a few progressive contractors.

The natural deduction from these facts is that if the contractor desires to operate as profitably as possible, and at the same time to reduce the element of risk in his elevating grader work to a minimum, he will study the various elements of his job with care and will pro- vide enough wagons that he can keep his grader work- ing at capacity. There are industries which to-day make all of their profit out of the use of materials formerly wasted. The situation of the elevating erader contractor is somewhat analagous in that as his work is now conducted team time is wasted in large amounts. One way of utilizing waste team time has been mentioned. Others could, no doubt, be sug- gested. The point is that every time a team stands idle when it could be made to produce something valueislost. Salvaging this value will prove profitable to any contractor who will undertake it seriously and methodically. If, to his efforts to salvage lost time he will add a serious study of those elements in this sort of work which are responsible for its present specula- tive aspects, particularly the element of haul, he should have little trouble in avoiding the financial troubles

so often encountered by those operating in this field.

(Continued from p. 58)

that maintenance costs on macadam roads are approxi- mately one-sixth as much per mile per vehicle as those on gravel roads, and in individual cases much less than this amount.

Even estimating 1,000 vehicles per day instead of 500 as the capacity of a gravel road, reference to the 1930 forecast map (Fig. 10) will indicate that a considerable mileage of gravel roads on the Maine primary system Beeald be reconstructed with more durable surfaces within the next six years.

On the basis of a maximum capacity of 1,000 vehicles per day for gravel-surfaced highways, the following pro- gram for the improvement of Maine highways is sug- gested for the period 1925 to 19380:

1. Construction of high-type pavements on the heavy- traffic routes.

2. The heavy-traffic routes included in the suggested improvement program, listed below, are divided into three groups based on density of traffic, the type of traffic on each highway, and the urgency of the need for immediate improvement.

3. It is suggested that the routes in Group | be im- proved first, those in Group II second, and those in Group III last.

4, Because of the greater total traffic as well as the larger number of motor trucks per day on the highways in Group I, high-type pavements are suggested for this group.

‘ BeOn the basis of Maine construction and mainte- nance experience it is believed that bituminous mac- adam, of the type now being constructed in the State will adequately serve the present and future traffic on

the highways included in Groups II and III for the ex- pected life of the bituminous-macadam type of con- struction.

6. In the selection of the surface type for highways in Groups II and III consideration should be given to the present type of surface on sections of the highways included in these groups.

7. Following is a description of the highways included in each group:

Primary system

Group I: Kittery— Portland—Brunswick. Portland—Auburn—<Augusta. Augusta— Gardiner. Waterville— Fairfield. Bangor—Oldtown.

Group II: Brunswick—Gardiner. Brunswick—Belfast. Brunswick—Auburn. Augusta— Waterville. Fairfield—Bangor via Newport. Bangor—Ellsworth. Waterville—Oakland.

Group III: Belfast—Bangor. Bangor—Ellsworth via Orland. Ellsworth—Bar Harbor. Fairfield—Skowhegan. Wells—Berwick. Portland—Bridgton—State line. Gray—Norway. Auburn—Farmington—Strong. Newport—Dover. Perry—Calais. Houlton—Presque Isle—Van Buren.

Secondary system Group I: Portland— Westbrook. Group IT: Auburn—Mechanic Falls. Wells—Sanford.

Budget requirements for this period can be estab- lished by computing the mileage of each type to be constructed (total mileage of designated routes less improvements already made) and estimating the costs of such construction. If estimated available revenues over

the period are not sufficient to meet such expenditures, the possibility of a bond issue to be retired from funds derived from an increased gasoline tax is suggested.

It is estimated that a gasoline tax of 1 cent per gallon will yield approximately $4,500,000 during the six-year period 1925 to 1930, inclusive. An increase of this tax from 1 to 3 cents per gallon would provide approxi- mately $9,000,000 in additional revenue.

During this same six-year period license fees, assum- ing no change in fees, may be expected to yield approxi- mately $17,000,000, making a total of $21,500,000 from license fees and a gasoline tax of 1 cent per gallon, or a total of approximately $30,000,000 from license fees and a gasoline tax of 3 cents per gallon.

NEW TESTING: DEVICES I DEVELOPED

Three new testing devices for the use of the highway engineer have been developed by the Division of Tests of the Bureau of Public Roads.

A test for the consistency of concrete in the field has

been devised as a substitute for the slump test, which is not particularly reliable under all conditions. The method is particularly adapted for concrete paving and other work in which a relatively dry consistency can be employed. It is based upon the principle that, within working limits, the consistency of freshly mixed concrete is proportional to the weight which will be retained upon a plate of given diameter when the con- crete is deposited on it in a standard manner. The device consists of a truncated cone large enough to hold about 75 pounds of wet concrete, supported by an angle-iron frame above a circular plate 15 inches in diameter, which in turn rests upon a spring balance.

The method of testing is as follows: The apparatus is placed upon the subgrade and the cone is filled with concrete immediately after the batch has been de- posited by the bucket. Immediately after filling the cone a removable slide at the bottom is withdrawn and the concrete flows out upon the plate. If the mix is either very dry or very wet, a larger quantity will roll or flow over the edges of the plate than if it is moderately dry. The plate is supported above the spring balance by two cams which take the weight of the concrete off the spring until it has all been de- posited. By turning a handle which revolves the sup- porting cams the concrete upon the plate can then be weighed. It has been found that for a 15-inch plate the usual variations in the amount of water in a 1:2:3 paving mix will cause a difference in weight of from 20 to 50 pounds. Experiments have indicated that for machine-finished work the proper consistency to use is one which will give the greatest weight of concrete retained upon the plate. For hand-fin- ished work a mix slightly wetter than this would probably have to be used. This device has been tried on actual construction and it appears to be of practical value. A more complete description of the process, together with test data illustrating the use of the apparatus, will appear in an early issue of Pusxio Roaps.

Work has also been carried forward on a device designed to register the intensity of pressure used during the molding of Portland cement mortar bri- quettes. Considerable latitude has always been allowed operators in regard to this detail of cement testing, resulting in quite appreciable variations in manipu- lation, which undoubtedly affect test results. The device consists of a small weighing platform approxi- mately 15 inches long and 4 inches wide, large enough to hold a glass plate and a three-gang briquette mold. The device is so arranged that an electric contact is made when a certain pressure is exerted on the briquette by the operator, lighting a white light in the front of the apparatus. Another contact, which when made shows a red light, may be set for a pressure beyond which the operator should not go. In determining whether an operator is using the proper pressure it is only necessary for him to mold a set of briquettes on the weighing platform and to note whether the pressure he exerts is sufficient to light the white light but not the red light. Both of the contact points are adjustable so that any pressure within working limits may be recorded.

GS,

particularly interested. nor to send free more than one copy of any publication to any one person.

ROAD PUBLICATIONS OF BUREAU OF PUBLIC ROADS

Applicants are urgently requested to ask only for those publications in which they are

The Department can not wndertake to supply complete sets The editions

of some of the publications are necessarily limited, and when the Department’s free supply is erhausted and no funds are available for procuring additional copies, applicants are referred to the Superintendent of Documents, Government Printing Office, this city, who

has them for sale at a nominal price, wnder the law of January 12, 1895.

Those publica-

tions in this list, the Department supply of which is exhausted, can only be secured by purchase from the Superintendent of Docwments, who is not authorized to furnish pub-

lications free.

ANNUAL REPORT

Report of the Chief of the Bureau of Public Roads, 1924.

No.

105. F136. 220. 257. *314. *347. *370. 386. 387. 388. 390. *393. 407.

*463. *532.

*537. *583. *586.

*660. *670.

*oOT, *704. *724.

*107¢. *1132.

DEPARTMENT BULLETINS

Progress Report of Experiments in Dust Prevention and Road Preservation, 1913.

Highway Bonds. 20c.

Road Models.

Progress Report of Experiments in Dust Prevention and Road Preservation, 1914.

Methods for the Examination of Bituminous Road Materials. 10c.

Methods for the Determination of the Physical Properties of Road-Building Rock. 10c.

The Results of Physical Tests of Road-Building Rock. 15ce.

Public Road Mileage and Revenues in the Middle Atlantic States, 1914.

Public Road Mileage and Revenues in the Southern States, 1914.

Public Road Mileage and Revenues in the New England States, 1914.

Public Road Mileage in the United States, 1914. A Summary.

Economic Surveys of County Highway Improvement. 35c.

Progress Reports of Experiments in Dust Prevention and Road Preservation, 1915.

Earth, Sand-Clay, and Gravel Roads. 15c.

The Expansion and Contraction of Concrete and Concrete Roads. 10c.

The Results of Physical Tests of Road-Building Rock in 1916, Including all Compression Tests. 5c.

Report on Experimental Convict Road Camp, Ful- ton County, Ga. 25c.

Progress Reports of Experiments in Dust Prevention and Road Preservation, 1916. 10c.

Highway Cost Keeping. 10c.

The Results of Physical Tests of Road-Building Rock in 1916 and 1917. 5c.

Typical Specifications for Bituminous Road Mate-

rials. 10c. ; Typical Specifications for Nonbituminous Road Materials. 5c.

Drainage Methods and Foundations for County Roads. 20c.

Portland Cement Concrete Roads. 15c.

The Results of Physical Tests of Road-Building Rock from 1916 to 1921, Inclusive. 10c.

No.

REPRINTS

Vol.

Vol. Vol.

Vol. 10, No. Vol. 11, No.

. *338. Macadam Roads.

. *727. Design of Public Roads.

1216. Tentative Standard Methods of Sampling and Test- ing Highway Materials, adopted by the American Association of State Highway Officials and ap- proved by the Secretary of Agriculture for use in connection with Federal-aid road construction.

1259. Standard Specifications for Steel Highway Bridges, adopted by the American Association of State High- way Officials and approved by the Secretary of Agriculture for use in connection with Federal-aid road construction.

1279. Rural Highway Mileage, Incomes and Expenditures, 1921 and 1922.

DEPARTMENT CIRCULAR

. 94. TNT as a Blasting Explosive.

FARMERS’ BULLETINS

oC. *505. Benefits of Improved Roads. 5c.

SEPARATE REPRINTS FROM THE YEARBOOK

5c. *739. Federal Aid to Highways, 1917. *849. Roads. 5c.

OFFICE. OF PUBLIC ROADS BULLETIN

*45, Data for Use in Designing Culverts and Short-span Bridges. (19138.) 15ce.

OFFICE, OF THE SECRETARY CIRCULARS

49. 59.

63. ap

DCs

Motor Vehicle Registrations and Revenues, 1914.

Automobile Registrations, Licenses, and Revenues in the United States, 1915.

State Highway Mileage and Expenditures to January PeLoLe:

Width of Wagon Tires Recommended for Loads of Varying Magnitude on Earth and Gravel Roads. 5¢

Automobile Registrations, Licenses, and Revenues in the United States, 1916.

Rules and Regulations of the Secretary of Agriculture for Carrying out the Federal Highway Act and Amendments Thereto.

FROM THE JOURNAL OF AGRICULTURAL RESEARCH

Effect of Controllable Variables Upon the Penetration Test for Asphalts and Asphalt Cements.

Apparatus for Measuring the Wear of Concrete Roads.

A New Penetration Needle for Use in Testing Bituminous Materials.

Toughness of Bituminous Aggregates.

Tests of a Large-Sized Reinforced-Con- crete Slab Subjected to Eccentric Con- centrated Loads.

73. 161.

17) D=2.

ONO:

OWNO: 5, No.

20, D-4. 24, D-6.

Dla 10, D-15.

* Department supply exhausted.

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