Thus, as the evidence on the preceding pages shows, cities are of very great importance in the movement of most interregional and long-range traffic. It was on this fact as well as on its general knowledge that the most concentrated masses of population and industry are located in the cities, that the Committee determined to base its selection of routes primarily upon the principle of the interconnection of important cities.
ACCOMMODATION OF SHORT-RUN TRAFFIC MOVEMENTS
As important as the interconnection of cities is, however, ideal directness of connection between the largest centers was not attempted, All highway traffic is a composition of long-range and short-range movement, and the highway planning surveys have shown that the latter is the predominant element on all roads. Normally, for example, about 85 percent of all trips are for less than 20 miles, and only about 5 percent for more than 50 miles.
In the selection of routes, therefore, the Committee has deemed it desirable to deviate from ideally direct lines of connection between the larger regional centers in order to connect en route as Many as practicable of the smaller urban centers.
Large and small are relative terms, however. The question upon which the Committee had to reach a decision was that of the general order of cities to be considered as primary points of connection. This decision would determine the extent of the system selected.
In applying the terms “large” and “small” to the problem in hand the Committee has considered both the population and the industrial importance of the cities. It has used its best judgment in determining the centers of primary connection and also the extent of desirable deviation from direct connection between these primary points in order to join in the system, urban communities of lesser importance.
MAXIMUM UTILIZATION
To connect all communities classified as urban would require inclusion in the system of a large part of the Nation’s 3,000,000-mile rural road system. Such a system would serve a very large part of the total highway traffic, but its average intensity of usage would be low by reason of the inclusion of much lightly traveled mileage. Obviously, it would be a much more extensive system than any that could properly be described as a major interregional system.
To go to the other extreme, it would be possible to select a system that would connect only, or mainly, the very largest cities of the country. It might be possible to accomplish this with a few transcontinental highways in each direction, though the connection would be indirect except between cities joined by the same route, and such a system would serve conveniently and fully only a very small part of the highway traffic of longer range. It would miss connection with many of the larger cities in its direct courses between the very largest cities. It would, therefore, traverse long distances, particularly in the West, where there would be little traffic to serve. Hence the average intensity of usage of such a system would probably be less than that of a larger system that would touch more, even though smaller cities.
