| Acceptable for existing roads |
Desirable for new or widened roads
| ||
| Grades (over 500 feet long): | |||
| Mountainous areas | Any existing | 6 percent | |
| Nonmountainous areas | do. | 4 percent | |
| Curvature : | |||
| Mountainous areas: | |||
| Heavy grading | do. | 14 degrees | |
| Other | do. | 6 degrees | |
| Nonmountainous areas: | |||
| Present average daily traffic less than 600 | do. | 10 degrees | |
| Present average daily traffic 600 and over | do . | 4 degrees | |
STANDARDS APPLICABLE TO URBAN AREAS
For the improvement of bridges and roads located in urban areas, the only items of the foregoing rural-area standards that are directly applicable are those for vertical clearance of bridges and underpasses and for the strength of paveme_nts. The only other feature of design for which it is practicable to prescribe a general urban-area standard is the load capacity of bridges, and for that feature the standard H–20 design loading of the American Association of State Highway Officials (see pls. 7 and 8) is recommended as more consistent with the greater frequency of application of extremely heavy gross loads to be expected generally in such areas. The horizontal clearance of bridges, width of pavements, gradients, and curvature in urban areas can be determined only after consideration of conditions peculiar to each location, and shoulders are not employed in urban street construction.
THE APPLICATION OF DESIGN STANDARDS
Some apprehension has been evidenced that the foregoing standards of design for roads and bridges might be arbitrarily enforced on all defense projects without reference to the particular conditions surrounding each project undertaken as a defense facility. No such policy has been given consideration. It would be a very unintelligent approach to the solution of the many problems. For the purpose of securing a reasonable measure of the adequacy of the highways to serve the needs of the defense operations, it has been necessary to use an accepted yardstick. The actual planning of the individual projects is being, and will be, worked out in full cooperation with the State highway departments. The organized engineering and administrative abilities of these organizations are essential to the success of the defense-highway programs and constitute the most important contribution to the strengthening of the national security.
Appendix IV
GENESIS AND CHARACTER OF THE STRATEGIC NETWORK
The strategic network in its present form is not a haphazard or theoretical collection of lines on a map. Its conception goes back more than two decades, and through this period the earnest attention of both State and Federal agencies has been devoted to perfecting the plan of interconnected routes that would best serve civil needs in times of peace and the defense needs in times of a national emergency.
