The sudden decision of whether to stop or go when the traffic signal changes from green to yellow at a signalized intersection often leads to drivers making incorrect judgments. The inability to perform either option successfully is attributed to the existence of dilemma zones (DZs). DZs often form at high-speed signalized intersections and occur when an intersection is hidden or occurs after a long gap. One way to avoid DZs is to advocate stopping at the intersection through Advance Warning Signals (AWSs). This study evaluates the effectiveness of AWS devices in providing DZ protection to drivers at two intersections in Utah: one in Brigham City and the other in St. George. The AWS in Brigham City also was reinforced with advance detection (AD) technology. The Utah Traffic Lab compared the intersections with AWS to an intersection without AWS. Findings showed that the AWS in St. George was not effective in reducing the number of drivers in DZs. Although 90% of drivers responded positively by reducing their speed when the signal was flashing, most of them reserved their decision to stop or proceed until they were close to the intersection. St. George had 1.15 percent more vehicles in the DZ than the control intersection. In contrast, the AWS setup at Brigham City was effective in reducing vehicles in the DZ. There were 1.4% fewer vehicles in the DZ than at the control intersection. The combined AWS-AD setup in Brigham City may have contributed to this effectiveness. Because the study did not yield conclusive results on the effectiveness of AWS systems, it is recommended that a detailed study be conducted at potential AWS locations before any future installations.

  • Record URL:
  • Supplemental Notes:
    • This research was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
  • Corporate Authors:

    University of Utah, Salt Lake City

    Department of Civil and Environmental Engineering
    122 South Central Campus Drive
    Salt Lake City, UT  United States  84112

    Mountain-Plains Consortium

    North Dakota State University
    Fargo, ND  United States  58108

    Department of Transportation

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    Utah Department of Transportation

    4501 South 2700 West
    Salt Lake City, UT  United States  84114-8410
  • Authors:
    • Martin, P T
    • Kalyani, V C
    • Stavanovic, A
  • Publication Date: 2003-11


  • English

Media Info

  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 50 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00980585
  • Record Type: Publication
  • Report/Paper Numbers: MPC Rept. No. 03-155
  • Created Date: Oct 31 2004 12:00AM