necessary, limited-access belt lines should also be provided; and all small communities should be bypassed—not entered. In general alinement the routes should be directed toward the center of large cities and past the sides of small towns, the line between large and small communities being drawn in each section between cities of such size as to contribute either (1) the larger or (2) the smaller part of the expected traffic on the route at their boundaries.
The standards of grade and curvature should be substantially the same as previously considered for the proposed toll-road system, varied slightly in concession to the more difficult or expensive locations. All railroad grade crossings should be eliminated and all highway intersections should either be separated, closed, or positively protected according to the importance of the intersecting roads.
Lane widths should be the same as those proposed for the toll highways, and pavements more than two lanes wide should be provided where traffic exceeds 2,000 vehicles per average day. Wherever it is probable that an original two-lane pavement may have to be increased in width, the original pavement should be laid off-center of the right-of-way.
The right to limit access should be acquired at all points and should be exercised wherever and whenever the amount of entering vehicles is likely to endanger appreciably, or interfere materially, with the freedom of movement of the main stream of traffic. Approaching large cities and elsewhere, if necessary, bordering local-service roads should be provided.
Right-of-way width in rural areas generally should be not less than 300 feet, in urban areas not less than 160 feet. And here, it may be observed again, as in respect to the various classes of city and city-vicinal facilities previously discussed, lies the crux and the initial and greatest difficulty of effecting the type of direct rural facility proposed.
SECONDARY AND FEEDER ROADS
The great preponderance of highway traffic in the United States is served by the rural roads included in the Federal-aid and State highway systems and by city streets. Local rural roads administered by county and lesser governmental units, although they comprise the large percentage of the total rural highway mileage, serve a relatively small percentage of the total vehicle-mileage.
As shown graphically in plate 60, it is estimated on the basis of results obtained by the highway planning surveys of 17 typical States that the main highways, comprising the Federal-aid and State highway systems and their transcity connections, serve approximately 57 percent of the total vehicle mileage on all roads and streets, although these systems constitute only 11 percent of the total mileage. The local streets of cities, constituting only 6 percent of the total road and street mileage, serve approximately 30 percent of the total traffic expressed in vehicle-miles.
Contrasting with these more heavily traveled highway and street facilities, the county and other local rural roads, which constitute approximately 83 percent of the total road and street mileage of the country serve only about 13 percent of the total traffic.
As these relative percentages indicate, problems incident to the service of large volumes of traffic are found almost exclusively on the Federal-aid and State highway systems and on the streets of cities.
