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these counties traversed were inhabited in 1940 by 25,862,000 persons or 45.2 percent of the entire rural population of the United States. The evidence of appropriate selection in this respect is marked in each geographic region. It is naturally more striking in regions with large variations of rural population. It is less conspicuous in regions where rural population is more uniformly spread, with either a relatively high or relatively low average density.

Location in relation to manufacturing activity.—Unquestionably any limited system of interregional highways that may be designated should, within the limits of mileage adopted, provide transportation facilities for as much as possible of the manufacturing industry of the country. Where manufacturing activity exists in greatest volume, there it may be assumed are the points of origin and destination of the greatest volumes of motortruck traffic. The interregional system should provide for the service of this traffic as well as passenger-car traffic.

In expressing this view, however, the Committee does not suggest that there is need of special highway facilities for the accommodation or encouragement of long-distance trucking. All the evidence amassed by the highway-planning surveys points to the fact that the range of motortruck hauls is comparatively short. There is nothing to indicate the probability of an increasing range of such movements in the future.

The length of truck hauls will be determined in the future as it has been in the past, by the competitive advantages at various distances of other modes of transportation. The probable early development of an efficient commercial air-freight service, together with the keener competition of a rejuvenated rail service, would seem to forecast a future shortening rather than a lengthening of average highway-freight hauls.

The volume of highway-freight movements in the future may be expected to be greatest on highways joining the centers of greatest industrial activity. Such highways should be incorporated, as far as possible, in the interregional system.