Page:America's Highways 1776–1976.djvu/409

 The Snow Road Bridge over I-496 near Lansing, Mich., is an example of modem safety design. Slanted back slopes and the absence of side piers on either end make safe vehicle recovery possible.

The 1956 Interstate standards made a further breakthrough in stating positive requirements for design with full access control throughout that System and for use of higher realm geometric design values as needed for operations at speeds of 60 m.p.h. and above.

During 1959 and again in 1966, a special AASHO Safety Committee conducted a nationwide survey of highways which resulted in published reports enumerating design details to provide greater safety. The second of these, Highway Design and Operational Practices Related to Highway Safety, 1967, soon known as the “Yellow Book,” included recommendations on the current highway design and practices to attain a higher degree of safety in both State and local agency actions. Responding, Federal policy directives called for utilization of the report recommendations on all project plans designed for a speed of 50 m.p.h. or more and a corrective program to apply the findings on existing highways. The report was updated and reissued in 1974 with the same title.

One of the newly advocated features from these studies was the “clear roadside” concept, which by 1966 had been started in a few States. During the early 1960’s, it became evident through accident analyses that about one-third of all accidents were single vehicle, run-off-the-pavement types, a high proportion of which proved to be of high severity on collisions with an object on the roadside, such as a rock, large tree, or steep cut slope. Some of these objects were highway elements such as culvert headwalls, rigid sign posts, lighting standards, bridge piers, etc. Better design and correction programs for safety were needed to provide traversible roadsides of a width well beyond the shoulder that was free of all formidable objects and reasonably flat and rounded so that off-roadway drivers would have a chance to recover control of their vehicles. Actions taken included lengthening culverts and overcrossings, moving sign supports or using the breakaway type, eliminating protruding drainage inlets, flattening and rounding roadway slopes, and providing tested-types of crash cushions at bridge abutments and between diverging 403