The relationship of the timing of the traffic signal clearance intervals (yellow phase plus red in all directions) to traffic flow, and crash rates at signalized intersections was examined. Specially designed traffic data logging devices provided data on the presence and speed of vehicles, and signal timing for 91 signalized intersections throughout the United States. Results showed that intersections with more adequate clearance intervals had substantially fewer rear-end and right-angle crashes than those with less adequate clearance intervals. The observed flow of traffic through the intersections after yellow onset was largely unaffected by variation in the lengths of clearance intervals, thus the proportion of drivers exposed to cross-street traffic decreased as the clearance interval lengths increased. Ideally, clearance intervals should be long enough to allow slower traffic approaching the intersection to cross before the cross-street traffic starts. However of the intersections in this study, the group with the highest average crash rate also had the slowest average crossing speeds, the widest cross streets, and the shortest and least adequate clearance intervals. Crash increases associated with deficient clearance intervals may be caused by abrupt stops by drivers who are reluctant to traverse wide cross streets with traffic waiting to start-up and by vehicles unable to clear the intersection under cross-street red protection.

  • Corporate Authors:

    Insurance Institute for Highway Safety

    1005 North Glebe Road
    Arlington, VA  United States  22201

    PRC Voorhees Company

    1500 Planning Research Drive
    McLean, VA  United States  22102
  • Authors:
    • ZADOR, P L
    • Stein, H
    • Shapiro, S
    • TARNOFF, P
  • Publication Date: 1984-6

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 29 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00395304
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: HS-037 886
  • Files: HSL, TRIS, USDOT
  • Created Date: Jun 30 1985 12:00AM