standards superior to those required by the currently realized or immediately expected traffic. These two considerations have instead generally forced the adoption of “stage construction” as a practical expedient.
Under this policy, initial improvements have often been designed to meet only the imperative requirements of the realized traffic. More adequate improvements have been delayed by sheer necessity. Roads previously unimproved have been partially improved by grading and drainage, with surfacing deferred until a later date. Narrow surfaces have been built where it was definitely anticipated that later widening would be required. Initial thin surfaces have been constructed with the intention later of superimposing thicker or more durable surfaces. Existing weak and narrow bridges too costly to replace at once have been retained as long as possible, with safeguards to permit continued use without excessive hazard . And, finally, narrow rights-of-way, and grades and alinement known to be somewhat inadequate, have had to serve.
All of these expedient measures were adopted so that available funds could be spread over a greater mileage and provide at least a reasonable degree of improvement on many sections of road that otherwise would have remained wholly unimproved for an indefinite period. As a result, the primary highway system was steadily, if adequately, improved over a period of about 15 years. By 1935, these most important roads presented no positive obstruction at any point to the normal flow of ordinary traffic. Conditions at many points, however, still imposed definite limitations on the convenience and safety of traffic.
The end of the pioneer period of road improvement may be said to have been reached by 1935. Then, but not until then, it became possible to do far-sighted planning of the construction that will eventually be required to improve the entire system adequately and consistently. Prior to that time, any appraisal of the adequacy of the main highway system for national defense, or for ordinary civil and commercial uses, would have revealed numerous weaknesses. The greatest of these would have been the entire lack of improvement on many sections. The superior necessity of initial improvement where no improvement whatever existed would have rendered largely impracticable any really effective attention to the many other weaknesses .
This initial improvement bad been completed by 1935, but in considerable part the other defects still remain. However, it is now possible, by careful and consistent planning, steadily to reduce the number of such defects, bring the entire network up to modern standards, and meet the needs of a mature system of highway transportation. This statement applies, of course, to the relation between highway conditions and the needs of all civil and commercial traffic. In view of present plans for a modern mechanized army, it is especially pertinent to the relation between the roads and their probable uses for the national defense.
In 1935, in view of the considerable changes that had occurred since the preparation of the “Pershing map,” the War Department reconsidered the network indicated on that map, and issued a revision. This revised map was then used by the Public Roads Administration and the State highway departments as a guide in their subsequent
