Page:Highway Needs of the National Defense.pdf/48

32 For urban highways, right-of-way width will be determined by economic feasibility.

Control of access

Control of access shall be provided where State laws permit and where traffic conditions warrant. Where required, in the absence of permissive State laws, additional right-of-way should be provided sufficient for the construction of frontage roads with controlled access to the through highway.

Lane width

For two-lane rural highways on which traffic density in the thirtieth highest hour is less than 200 vehicles in one direction or 300 in both directions, a minimum lane width of 11 feet is required. For two-lane rural highways of thirtieth-highest-hour traffic density greater than the above, lane width shall be 12 feet.

For rural highways of four or more lanes, lane width shall be 12 feet.

For all urban highways lane width shall be 12 feet.

Divided highways

Divided roadways are required on all highways on which the two-direction traffic volume was 800 or more vehicles in the thirtieth highest hour of 1948. Division may be provided on highways of lesser traffic volume where such provision is less costly than the provision of the required passing sight distance for single two-lane roadways.

The width of median strip on divided highways shall be as follows:

Three-lane highways

Three-lane highways are not permissible.

Shoulder width

In mountainous areas shoulder width shall be a minimum of 4 feet, and elsewhere a minimum of 10 feet, measured to the intersection of shoulder and side-slope planes.

Railroad grade separations

Separation of grades shall be provided at all railroad crossings of two or more main-line tracks, and at all crossings of single main-line tracks on which there are six or more regular train movements daily.

Although by the agreed standards separations are required to be provided at crossings of single main-line tracks of five or less train movements daily only where justified by economic analysis, they were, for purposes of the cost estimate prepared for this report, provided at all such crossings.

Highway grade separations

Separation of grades is to be provided at all highway intersections where the sum of the two-direction traffic volumes on the intersecting roads in the thirtieth highest hour of 1948 was 2,000 vehicles or more,