a road, finally resulting in the worst places being at least temporarily bettered. The grade on the steepest hills is probably reduced somewhat and some of

es not produce an improvement that lasts, and sometimes it is not even of any great immediate benefit to

ords, there must be a road improvement policy which will be made effective through some agency that is so organized that its policies will be perpetuated an

f grades and the many other details of design may properly be adopted for a specific piece of work only after an a

d somewhat slowly, so that valuable devices and improvements in methods remain long unknown exce

an agency of continuing personnel which will supervise the preparation of suitab

or grade reduction or reshaping an earth road surface, while for the construction of paved roads, the plans must be worked out in considerable detail. The essential requirement is that there be given on the plans all information necessary to enable the construction to be carried out according to the intentions of the engineer, that all parts of the work fit together, that the culv

nce and economy to the users thereof. The degree to which the design will be effective will depend to a considerable extent upon the financial limitations imposed upon the engineer, but skill and effort on the plans will

ty reconnaissance will usually be sufficient. This is made by walking or riding over the road and noting, in a suitable book or upon prepared blanks, the information needed. The items of information recorded will usually be as follows: distances, grades, type of soil on the road and nature of existing surface, character of drainage, location of bridges and culverts and the type of each with notes as to its condition, location of railway crossings and notes as to type, location of interse

erits of the improved roads. Some special characteristic of a road, such as bad railroad crossings or a few bad hill

may be required finally to select the best

, a careful survey is made to furnish information for the preparation

long the center line of the existing road or parallel thereto. The topography is referenced to this line in such completeness that it can be reproduced on the plans. The level survey consists in taking levels on cross sections of the road at one hu

ve to the project, a plan is prepared which embodies a design presumed t

blem of

ad design, although in the actual design the consideration of these

way so far as possible. But the element of safety must not be lost sight of, and curves should not preclude a view ahead for sufficient distance to insure safety to vehicles. The necessary length of clear view ahead is usually assumed to be 250 feet, but probably 200 feet is a satisfactory compromise distance when a greater distance cannot be obtained at reasonable cost. To secure suitable sight distance, the curves must be of long radii, and where possible the right-of-way on the insid

r they shorten distances or reduce grades

om in the right-of-way, and enough additional right-of-way must be secured to permit the proper design. It is not necessary to provide an intersection that

to continue the paved surface across the intersecting road at normal width and make no provisi

is taken of the tendency of motor cars to skid toward the outside of the curve.

g.

ngle of superelevated surface c-d, with the horizontal c-a. R represents the radius of the curve upon which the vehicle is moving. w i

W

mv2

skid; hence the rate of superelevati

n θ

θ

refore, varies as the square of the veloci

rve is likely to be of such short radius that it is impossible to maintain the ordinary road speed around the curve, even with the maximum superelevation permissible. It is good practice to provide the theoretical superelevation on all curves having radii greater than 300 feet for vehicle speeds of the maximum allowed by law, which is generally about 25 miles pe

the theoretical supereleva

uperelevation for Various Degrees of

for providing for through traffic in both directions and for traffic which may turn in

rate of grade upon the energy required to transport a load over the highway. The forces that oppose the movement of a horse drawn vehicle are fairly well understood an

esistance of the road surface to the rolling wheel, resistance of the air

ce encountered, but there is always a certain amount of distortion of either road surface or wheel, or of both, which has the same effect upon the force necessary for translation as a slight upward grade. When both the tire and the road surface strongly resist distortion (as steel tires on vitrified brick paving), the resistance to translation is low but the factor of impact is likely to be introduced. Where impact is pres

d vehicles, the internal resistance consists of axle friction and friction in the driving mechanism, of which gear friction and the churning

he usual speed of the passenger automobile on the road becomes a very considerable part of the total resistance to translation. This factor has no significanc

fairly consistent when the inevitable variations in surfaces of the same type are taken into account. Table 4 is a composite made u

bl

tance of Road Surfaces

active for

cked and

dust

mudd

loo

el g

l loo

well-p

road

road-w

m-very

m-aver

asph

ic conc

ed bric

lock-g

lock-p

lest

e tram

lt bl

te bl

bl

ances to Steel

Road Condition

lb. Re

to

(unsurfaced) Good,

(unsurfaced) Good,

face asphaltic oil and screen

ce asphaltic oil and screeni

er-bound Good, ex

oncrete Good, exc

ct, good condi

macadam Good,

macadam Good,

d, in good cond

Good condition, soft, w

m, 1?-in. fine lo

nk Good condition,

ad Dust ? to 2

tiff, firm under

ose, not pack

n in Engineering News-R

that the load was being accel

otor truck at 2?

motor truck at

istance of motor vehicles, but the following tables are based

k, water-bonded and tar macadam, cinder and gravel road surfaces were obtained by A. E. Kennelly and O. R. Schurig in the research division

materials, at certain speeds per hour, ranging from about 8 to about 15.5 miles per hour. The result of the observati

bl

Condition of S

ist

l

r

m

r. Tr

ist

l

r

4 m

r

lt Go

Poor 2

ck Good

ock Good

lock Good

Slightly w

ith cement join

bonded Dry an

nded Fair, heavil

ded Poor, damp, so

dam Good

m Very sof

oles, soft, extrem

ir, hard

ir, dusty

g.

surface and opposite in direction to the motion when the load is ascending the hill and in the same direction when the vehicle is descending. In Fig. 8 W represents the

W t

1 × per cen

W × per

ent of grade, for each t

ton of load for each

de is therefore 20 lbs. per ton for each one per cent of grade and this

forces opposing the t

i + fp + f

h

resistance of

e to internal fric

due to impact of

stance du

which is positive when ascendi

e in pounds per

effort applied to the

r than F in order t

ny vehicle loaded for satisfactory operation on a level road with the power available, the limiting condition is the factor fg. If the load is such as barely to permit motion on a level road, any hill will stall the vehicle. Therefore, in practice the load is always so adjus

el road by draft animals, there is a limit to the rate of grade up

ble is therefore six times the average pull, but this is possible for only short intervals. A very short steep hill would afford a condition where such effort would be utilized. But for hills

re one requiring, to overcome the effect of grade, or fg,

fp + fa = 100 lbs. per gross ton on a level section of road, then the gross load for the team would be 3.6 tons. The same team could for a short time exert an additional pull of three times 360 lbs. or 1080 lbs. For

+ fi + fp + fa = 60 lbs. per gross ton on a level section of road, the gross lo

for roads to be surfaced with a material having low tractive resistance and the poor economy of adopti

consideration for main trunk line highways, but it is certain that for a

oving vehicles over grades up to 12 or 15 per cent, so that any grade that would ordinarily be tolerated on a m

potential energy and can be partially or wholly recovered when the vehicle descends a grade, provided the physical conditions permit its utilization. If the grade is so steep as to cause the vehicle to accelerate rapidly, the brakes must be applied and loss of energy results. The coasting grade is dependent upon the character of the surface and the nature of the v

n translating the vehicle down the grade, but also in overcoming resistances due to mechanical friction and the air. On long grades, a speed might be attained that would require the use of the brake or the same condition might apply on very stee

ill and the physical condition of the road permits speeds up to thirty-five or forty miles per hour grades of five per cent are permissible if the length does not exceed five hundred feet and grades of three per cent one thousa

than six per cent, it is questionable economy to reduce the grades that are already lower than the allowable maximum. It is especially unjustifiable to incur expense in reducing a grade from two per cent to one and one-half per cen

provide as flat grades as possible at the curves and to cut away the berm at the side of the road so as to give a view ahead for about three hundred feet. Whether a road be level or on a hi

ypes of G

y reason the driver loses control. These are usually strongly built, but would hardly restrain a vehicle which struck at high speed. But they are adequate for the protection of a driver who uses reasonable care. A typical guard rail is shown

rticularly likely to obstruct the view and should be cleared or cu

ondary roads, carrying perhaps 25 to 50 vehicles per day, may have an available traveled way 18 feet wide. Those more heavily traveled may require room for three vehicles to pass

ll the side ditches will be of small capacity or may be entirely omitted, but usually some ditch is provided. The transition from the traveled way to ditch should be a gradual slope so as to avoi

g.

a gridiron system, as is the case in many of the prairie states. The streams cross the highways at frequent intervals and the culverts can be placed so as effectually to prevent an increa

sable to provide tile for carrying the water under the road, instead of the culvert, and, by continuing the tile

nstructing weirs across the ditch at frequent intervals, thus

the drainage channel changes abruptly from a higher to a lower level, pa

side ditch along the road and culverts will be required to carry the water under the driveway. Driveways that cross a gutter by means of a pavement in the gutter are usually unsatisfactory, and to cross the gutter without providing a pavement is to insure stoppage

me states wild roses and other low bushes are planted to serve the two-fold purpose of assisting to prevent erosion and to beautify the roadside. In humid areas trees of any considerable size shade the road surface and are a distinct disadvantage to roads surfaced with the less durable materials such as s