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34 to keep pace with the average rate of development of abutting property on all roads having unrestricted access, the fast rate of development in favorably located areas close to access points on the selected routes must be great enough to compensate for the lack of traffic contributing development along the balance of the system. It seems doubtful that it would be great enough even were the selected routes operated as free facilities, but in the absence of a definite means of determining the extent to which these items balance, it is assumed that the average rate of development on such a system operated as a free facility would keep pace with the average rate of development on all routes. For a system of toll highways, a slower rate of development must be assumed.

In considering the probable faster rate of increase in the average length and number of long trips, it becomes apparent again that the allowance made for the selected routes operated as toll facilities should be different from that which would be made if they were operated as free facilities. This difference is caused by the fact that the more money people spend for tolls, the less they have left to spend for operation of their vehicles. However, this rate of increase should be greater for the selected routes, operated on either a free or toll basis, than the rate of increase for main highways, because the long trips, which tend to increase in number faster than short ones, form a larger percentage of the traffic on limited-access roads than on normal main highways.

A thorough consideration of all of these points indicates that it would be reasonable to assume that the trend of travel on the selected routes, operated as toll facilities, would increase approximately one-third faster than travel on all roads.

Before expanding the maximum estimates of 1937 traffic by application of these trends, one further factor must be considered. That factor is generated traffic which, for this purpose, may be defined as the traffic which results from a new desire for travel on the part of certain people who would not care to perform the same travel in the absence of the improved facilities. This traffic would appear during the first years of operation of the new facilities, after which time its entire effect upon the rate of increase may be assumed to be eliminated. It is estimated that 3 years after completion of a route this traffic would increase the total diverted traffic by 20 percent, if it were operated as a toll facility.

Using these relationships, the multiplying factors derived for converting the maximum estimates of 1937 traffic on the selected routes, operated as toll facilities, were 2.5 for 1960 traffic and 34.2 for the traffic of the entire period from 1944 to 1960, assuming that one-half of the system could be placed in operation January 1, 1944, and the remaining half could be placed in operation January 1, 1946.

NUMBER OF LANES REQUIRED FOR FREEDOM OF MOVEMENT OF TOLL-PAYING TRAFFIC

One of the elements of highway design most affected by the volume of traffic to be served is the width of the pavement or the number of lanes provided.

In determining the number of traffic lanes required for toll roads, it is necessary to base the determination upon factors that are not