But the common impression that provision of such routes would constitute invariably a complete, or even a substantially adequate, solution of the highway problem at cities is not well-founded. It is a fallacious conception of the need for adequate accommodation of the traffic moving over the rural highways. From the standpoint of the cities it fails as a solution of the most serious aspects of the problem.
The root of the fallacy, so far as the rural highways are concerned, lies in the fact that on main highways at the approaches to any city, especially the larger ones, a very large part of the traffic originates in or is destined to the city itself. It cannot be bypassed.
This fact was demonstrated by the Public Roads Administration in its report entitled “Toll Roads and Free Roads,” published in 1939,[1] by reference to studies of the origin and destination of traffic observed on U.S. 1 between Washington and Baltimore. A diagram presented in that report is here reproduced as figure 27. The text that accompanied it is as follows:
As shown by the topmost line in this graph, the total traffic on the route rises to a peak at each city line and drops to a trough between the two cities. Of this total traffic, that part above the highest of the horizontal lines represents movements of less length than the distance between the cities. At each city line this part consists of movements into and out of the city all of which are of shorter range than the distance to the neighboring city. The uniform vertical distance between the highest and the next lower horizontal lines measures the amount of traffic on the road moving between points in each city. The height of the next lower horizontal band represents the traffic moving between Washington and points beyond Baltimore; that of the next, the traffic moving between Baltimore and points beyond Washington; while the height of the lowest horizontal band measures the volume of the traffic moving between points that lie beyond both Baltimore and Washington. Of all the traffic shown as entering the two cities, only this last part plus that represented by one or the other of the next two higher bands can be counted as potentially bypassable around the two cities. At Washington this bypassable maximum is 2,269 of a total of 20,500 entering vehicles; at Baltimore it is 2,670 of a total of 18,900 vehicles. The remainder of the
An origin-destination study of the traffic on this same highway was made at an earlier date by Coverdale & Colpitts[2] at a point near Baltimore. It serves further to illustrate the manner in which the traffic approaching a large city by a typical main highway is distributed to the center and various quarters of the city and, via various other main routes, to points beyond the city.
Figure 28 is adapted from the report of this study. It shows that of a total of 5,874 vehicles approaching the city, 717 moved to the center of the city as their ultimate destination. Others, numbering 726, 398, 113, and 163, respectively, proceeded to ultimate destinations in the northwest, northeast, southeast, and southwest quarters of the city. A large number, 2,225 vehicles, went to points within the city (largely in the central portion) and returned the same day by the way they had come. Seventy-one vehicles, bound to points beyond Baltimore, made stops in the city before proceeding to their ultimate destinations, and the remainder, totaling 1,157, or 21 percent of the city-entering traffic, passed through the city and emerged by several other main highways en route to destinations beyond the city.
