This project is being 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 consists 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 will results in the smoothest traffic flow. Phase III will utilize this information, as well as the pertinent literature, to develop detailed specifications for a full-scale advisory system for testing on a public highway. This report covers the activities of Phase I and the preliminary results of the first two experiments of Phase II. The facilities, equipment and procedures developed are described as well as some of the problems encountered in their development. The first study of Phase II was concerned with determining what speeds drivers normally drive at under various conditions of reduced visibility. Fifity-one subjects maye a total of 144 fog runs at 100, 200, 300 and 400 foot visibilities. The drivers speed distributions were obtained and the 15th, 50th, and 85th percentile speeds calculated for each condition. The second study was intended to determine which of the percentile speeds from Study I would results in the smoothest traffic flow when used as a posted speed for each of the four visibilities. One hundred five subjects made a total of 140 runs under that 12 speed-visibility conditions. Although only a first level analysis has been completed, the results indicate that the posted speed sign had little or no effect (regardless of which percentile speed was posted) upon driver performance in terms of mean speed through the fog. Additionally, the presence of the posted speed was found to have a slightly deterimental effect upon traffic stability. This was evidenced by an increase in speed variance for the conditions of Study II when a posted speed was present over similar visibility conditions of Study I when the sign was not present. For Study II, little in the way of a systematic effect was found for the posted speeds within visibility conditions. A more detailed analysis of the data is suggested and is being conducted. The report also contains a description of the remaining studies in Phase II. /FHWA/

  • Corporate Authors:

    Oregon Department of Transportation

    State Highway Division, State Highway Building
    Salem, OR  United States  97310
  • Authors:
    • Lane, F D
    • Pfau, J L
  • Publication Date: 1975-5

Media Info

  • Pagination: 131 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00099905
  • Record Type: Publication
  • Source Agency: Federal Highway Administration
  • Report/Paper Numbers: FHWA-RD-75- 66 Intrm Rpt.
  • Contract Numbers: DOT-FH-11-7950
  • Created Date: Nov 5 1975 12:00AM