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108 publicly controlled margins will permit employment of various measures designed to abate the menace; among them roadside planting to obscure unwanted billboards, the prevention of parking on the traveled way, and control of the conditions of egress from and ingress to the highway at all bordering properties.

The need for such additional right-of-way width is not so great on the less frequented highways, because most of the developments complained of are only attracted by and associated with the denser traffic flows.

The need of modernizing improvements here suggested—improvements made necessary by the changes that have occurred in the speed and volume of traffic, and most of them involving important new right-of-way requirements—is present today on a large mileage of existing main highways in the State and Federal-aid systems, and on other roads of comparable importance, generally in the vicinity of cities. Specifically, the needed improvements include the reduction of excessive curvature; the flattening of heavy grades; an opening of longer sight distances; a general widening of pavement lanes; a construction of additional lanes and separation of opposing traffic where increased volume requires, and possibly also for the accommodation of slow vehicles on the heavier grades; the separation of grades at many railroad and highway intersections, and installation of protective cross traffic controls at others; the abatement of dangerous roadside conditions of all sorts; and a substantial improvement in the general directness of alinement between important objectives of the principal routes serving movements of the longer ranges.

All of these named improvements, except one, can be accomplished generally by local correction of, and addition to, the existing highways after acquisition of the new rights-of-way almost invariably required. The exception—the provision of more direct routes for long distance, interregional movements—will involve the construction of considerable lengths of new and more direct highways to be used in place of existing indirect roads by the through traffic. Usually the existing facility will remain in use for the service of the local traffic it was located originally to serve.

The abundance of information supplied by the State highway-planning surveys now makes it possible to decide upon the lines for such direct highways most useful for the accommodation of the ordinary peacetime movements. In consideration of this information and a knowledge of the general needs of the national defense received from previous advices of the War Department, a tentative selection of routes has been made, which, comprising a 26,700-mile system, is shown on the map reproduced as plate 57.

After further study, in which there should be a close cooperation with the Bureau of Public Roads by various agencies, particularly the War Department and the several State highway departments, it is now advisable by law to establish this or a closely similar system as the Primary Highway System of the United States.

The system tentatively selected is believed to include substantially every major line of interregional travel in the country. As shown on plate 58, it joins the populous cities of the United States, almost without exception, and one of its routes follows practically every of the lines along which the population of the country has moved one present settlement and along which it is still obviously thickest to its both in city and country.