To test the adequacy of the recommended system from the stand- point of industrial transportation, the committee has used the census reports of values added by manufacturing industries located in the various cities of the country, as a measure of the relative manufacturing activity of these cities and of the relative probability of intercity highway freight movement.
These values for all cities of 10,000 or more population are shown on the map, figure 7, by circles of various scaled diameters. Here again, as in the similar map (fig. 3) representing the relative populations of cities, it will be seen that the routes of the recommended system connect the cities represented by the largest circles, and within the limit of total mileage adopted, join or closely approach en route about as many as possible of the cities of larger manufacturing importance.
A comparison of figures 3 and 7 will show that while slight differences exist in the relative importance of cities when they are measured on the one hand by their populations and on the other by the values added by their manufactures, on the whole the similarity of the measurements is marked.
This similarity is further evidenced by a comparison of tables 3 and 5. The latter shows the value of manufactures added in the cities of 10,000 or more population that are on the system, in relation to the corresponding total for all cities of the same population range, while table 3 shows the population relation. In both instances the cities on the system are shown to be important beyond their number.
A comparison of the number of cities of 10,000 or more population reached directly by the recommended system and other systems investigated, and the values added by manufacture in these cities is shown in figure 8. From this figure it will be observed that the largest system investigated (78,800 miles) connects directly with about 75 percent of the cities of 10,000 or more population, and that these connected cities account for 90 percent of the value added by manufacture in this population group.
To reach directly all cities of 10,000 or more population it has been determined that the 78,800-mile system would have to be increased by at least 14,100 miles. This new and larger mileage totaling 92,900 miles is shown in figure 8 as the abscissa of the point representing 100 percent of the number of cities of 10,000 or more and of the value added by manufacture in all such cities.
From this figure it is manifest that the cities of 10,000 or more population connected by the recommended system are, in general, the more important manufacturing cities. Numerically only 54.5 percent of all cities of more than 10,000 population, they account for 83 percent of the total value added by manufacture in all such cities.
In contrast, the system reaching all of the cities is nearly three times as large and serves only an additional 17 percent of manufacturing activity.
