This project was conducted to develop preliminary design specifications for a speed advisory system for use during periods of reduced visibility (fog). 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 consisted of a series of interrelated experiments to identify optimum advisory information (sign messages and speed values), and the number, locations, and interconnections between signs which would result in the smoothest traffic flow. Phase III utilizes the information from Phase II, as well as the pertinent literature, to develop preliminary specifications for a full-scale advisory system for use on the public highway. Phase II contained six separate studies. Study I was concerned with determining the speeds drivers normally drive at various levels of reduced visibilities without special signing. Study II was to determine which of the three major percentile speeds (15th, 50th, 85th) from Study I would produce smoothest traffic flow when used as a posted speed. The main purpose of the third study was to determine driver response when other vehicles are present on the highway under conditions of reduced visibility. The 4th study investigated the effects of different types, amounts and display characteristics of advisory signing. Study V investigated the utility of centerline and edgeline delineation. The final study dealt with the effects of unreliable information presentation by advisory signing systems. (FHWA)
Abstract