Abstract
Preliminary design specifications for a speed advisory system for use during periods of reduces visibility (fot) are presented. Phase I of the program consisted of developing the necessary facilities, equipment and procedures to conduct controlled experimentation under various levels of fog density. Phase II consists of a series of experiments to identify optimum advisory information, and the number, locations and interconnections between signs which will result in the smoothest traffic flow. Phase III develops detailed specifications for a full-scale advisory system.