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42 CHARACTER OF THE APPROXIMATE LOCATIONS SELECTED

In accordance with criteria and standards previously established the selected routes were approximately fixed by detailed location on large-scale maps, chiefly county maps, prepared in connection with the State highway planning surveys. A typical section of one of these maps is shown in plate 27. The lines were located either by Bureau of Public Roads engineers resident in the several States or by engineers of the State highway departments, or both, working together. In all cases the locating engineers were intimately familiar with the areas in which they worked.

Wherever necessary a field reconnaissance was made. It is thus reasonably assured that the approximate locations chosen are practicable of development and conform closely to the criteria adopted. The field inspections also permitted a better judgment to be formed of the quantities of the various construction items that should be accounted for in the estimates of cost.

The alinements chosen extend as directly as possible from one major source of traffic to another, deviating from such direct lines to serve minor sources of traffic only where it has been estimated that the resulting increase of traffic would be substantial. Sources of traffic, in general, consist of cities and towns, intersecting highways, and points of travel interest, such as national parks, resorts, etc.

In all but two sections, totaling 94.2 miles, the detailed locations have been made entirely on new lines apart from existing roads. One of the excepted sections, 51.9 miles in length, lies along the Columbia River in Oregon; the other, 42.3 miles long, crosses the Sierra Madre Range north of Los Angeles, Calif. In these sections the alinement chosen coincides with that of existing highways because no other topographically feasible line could be found.

The chosen approximate locations bypass cities and towns, but pass sufficiently close to them, wherever possible, to attract their traffic. In detail, the locations are such that (1) control of access may be readily obtained wherever possible; (2) obstruction to the outward development of cities and interference with communication across the selected route are avoided to the greatest extent possible; (3) the cost of grade separation structures is reduced to the feasible minimum; and (4) a maximum feasible benefit of low land values is gained.

STANDARDS OF DESIGN ADOPTED

It was considered necessary that the design standards of the selected routes be sufficiently superior to the standards of existing roads to attract traffic, insure a maximum of safety and utility in their present use, and conform so far as possible to the probable requirements of future traffic. At the same time the standards were not set so far in advance of the requirements of existing traffic as to incur excessive initial costs which present users should not be asked to pay. For example, over three-fourths of the mileage of the routes, as designed, consists of two-lane roads, but to meet the possibility of future expansion to four lanes the initial pavement would be placed at one side of the right-of-way.