Interregional Highways/Standards and features of roadway location and design

by National Interregional Highway Committee

STANDARDS AND FEATURES OF ROADWAY LOCATION AND DESIGN

Any network of highways that may hereafter be designated officially as an interregional system should embrace as nearly as practicable, within the limits of mileage adopted and subject to the necessities of national extension and interconnection, those general routes along which the heaviest traffic moves or is likely to move in each region traversed. It has been the Committee's aim to select such a system and it believes that, insofar as its necessarily limited studies have permitted, it has made this selection in the system recommended in this report. This network, or a better system selected after more complete study, should be consistently constructed throughout, in all parts of the country, as a well-balanced whole, in the post-war years ahead.

There are existing roads that conform closely to all parts of the recommended system. There will be existing roads conforming more or less closely to any system that may be selected as a better modification of the system recommended. After any such system is finally agreed upon, whenever the improvement or reconstruction of any section of conforming highway is contemplated, it should be built on a location and to a standard of design that will make it a fit and lasting part of the complete interregional system that will be created by such sectional increments.

This incremental construction will be carried out under various auspices. In part, doubtless, it will be done by the Federal Government and States jointly; in part, by the States alone; in part by combined Federal, State, and city effort; in part by State and city cooperation; and possibly in part upon the completely independent initiative of cities. If, built in this manner, the interregional system is to achieve the high degree of consistency of design and utility that is desirable, two arrangements are necessary: First, there must be an agreement upon certain basic standards of roadway design and location, by all authorities likely to have a share of responsibility for its construction. Second, there must be a determination on the part of these authorities and the public that whatever work at any time is done on routes generally conforming to the selected system shall be well done in accordance with the agreed standards. In no other way will it be possible to achieve the timely completion of a consistently useful and wholly satisfactory interregional highway system.

To this end the Committee proposes herein certain basic standards for general adoption. It recommends that these standards be widely considered by all possible cooperating authorities, and that after there has been sufficient opportunity for such consideration, occasion be made at the initiative of the Public Roads Administration to effect agreement as complete and general as possible upon these or other acceptable standards. The Committee recommends further that the agreed standards be made the required basis of any cooperation on the part of the Federal Government in the construction of any route conforming to the interregional highway system as it is finally designated.

Prefatory to the standards proposed, the Committee offers the following fundamental recommendations:

1. The interregional highway system, as it is hereafter constructed or improved, shall provide or allow for the subsequent provision of facilities capable of serving safely and efficiently a mixed traffic of passenger automobiles, motor busses, and motor trucks, and tractor-trailer and semitrailer combinations, of a volume of each of the constituent elements estimated to be that which will exist 20 years from the date of construction.

2. All roadways and structures built on the interregional system shall provide, either in their immediate design or feasible modification thereof, for the passage and support of vehicles and combinations of vehicles of the following dimensions and weights, in the frequency and distribution of such dimensions and weights to be expected 20 years from the date of construction:

Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	96 inches
Height. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12½ feet.
Length (over-all, including bumpers and load):
Single vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	35 feet.
Tractor-semitrailer combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	50 feet
Other combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	60 feet.
Axle load[1] on pneumatic tires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18,000 pounds.

1. Defined as the total load on all wheels whose centers may be included between 2 parallel transverse vertical planes 40 inches apart.

Gross weight on any vehicle or combination of vehicles according to the formula.

$W=C(L+40)$

In which:
W = gross weight of vehicle in pounds.
L = Length in feet between the forward and rear axles of the vehicle or combination of vehicles or any group of axles thereof.
C = A coefficient with the following values:
For values of L less than 18 feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	650
For values of L equal to or greater than 18 feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	750

3. For purposes of the design of highway facilities and the application of standards and conditions hereafter recommended, all sections of the interregional system in or approaching a city or town and at least 1 mile long, along which intersecting roads or streets average one-quarter mile or less apart, shall be considered as urban sections, regardless of their locations within or without the corporate limits of cities. All other sections of the system shall be considered as rural sections, regardless of their location within or without the corporate limits of cities.

4. All rural sections of the system shall be designed at all points and in all respects for safe travel by passenger vehicles at a speed of not less than 75 miles per hour, and by trucks and tractor combinations at a speed of not less than 60 miles per hour in flat topography. In more difficult terrain the speed for which the highway is designed may be reduced; but in no case to less than 55 miles per hour for passenger vehicles and 35 miles for trucks and tractor combinations in mountainous topography. All rural sections shall provide a sufficient number of traffic lanes and other facilities so that at no time, except during infrequent peak hours, will it be necessary because of the interference of other vehicles to reduce the average running speed to less than 50 miles per hour. All two-lane rural sections, on which the sight distance provided will not permit safe passing at the above design speed for passenger vehicles, shall be appropriately and conspicuously marked as no-passing zones or as zones in which passing is unsafe.

5. All urban sections of the system shall be designed at all points and in all respects for safe travel by passenger vehicles at a speed of not less than 50 miles per hour, and by trucks and tractor combinations at a speed of not less than 35 miles per hour. All urban sections of the system shall provide a sufficient number of lanes and other facilities so that at no time, except during infrequent peak hours, will it be necessary because of the interference of other vehicles to reduce the average running speed to less than 40 miles per hour.

6. Wherever financially feasible, the system shall provide continuous lateral space and adequate support for standing and disabled vehicles of the recommended maximum sizes and weights, clear of the road surface or pavement.

7. All road surfaces, pavements, and structures on the system, when maintained with a reasons expenditure of effort, sha capable of supporting vehicles of the recommended weights without reduction of either weight or speed at any season of the year.

Consistent with the foregoing fundamental recommendations, the Committee proposes for general adoption, basic standards of road and structural design, applicable to the selected interregional highway system. These basic standards are contained in appendix V.