Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections

Red-light running is one of the most common causes of intersection crashes. Research shows that yellow interval duration is a significant factor affecting the frequency of red-light running, and increasing yellow time to meet the needs of traffic can dramatically reduce red-light running. However, it is not known if the reductions in red-light running translate into reductions in crashes and injuries. Longer yellow times may increase the zone in which drivers have the option of safely stopping or going and thus increase the potential for conflicts and risk of rear-end crashes. Furthermore, there is no consensus on how the yellow and all-intervals should be timed. The assumed reaction time and deceleration rates for timing yellow lights are based on limited research of car drivers that is a quarter century old. The effects of heavy vehicles are ignored although trucks require longer distances to stop especially at higher speeds. Given the aging of the population, research is needed to determine normal reaction times and deceleration rates for use in timing yellow change intervals. This should be done for intersection approaches covering a range of speeds, grades, vehicle types, surface condition (wet/dry), and turning movements. The end product would be improved guidelines for timing change intervals. Most studies on driver behavior during yellow change intervals were conducted more than 25 years ago and the observations were limited to a few hours at a few sites. The research indicates that if the deceleration required to stop is less than 8 ft/sec<sup>2</sup> most drivers will stop and if it is more than 12 ft/sec<sup>2</sup> most drivers will continue through the intersection. None of the research appears to investigate behavior or needs of truck drivers or assess whether these values apply for all approach speeds. Most studies on the effects of all-red intervals report accident reductions; however, these studies were limited to a 1-year-after period. Long-term evaluations in Indiana and Minnesota found accidents increase after the first year resulting in no net reduction. Bonneson and Son (2003) and Zador et al. (1985) found that longer yellow interval durations consistent with the ITE Proposed Recommended Practice(1985) using 85<sup>th</sup> percentile approach speeds are associated with fewer red-light violations, all other factors being equal. Bonneson and Zimmerman (2004) found that increasing yellow time in accordance with the ITE guideline or longer reduced red light violations more than 50 percent. Van Der Host found that red light violations were reduced by 50 percent 1 year after yellow intervals were increased by 1 second. Retting et al. (2007) found increasing yellow time in accordance with the guideline reduced red-light violations on average 36 percent with higher reductions. This project will develop guidelines for timing yellow and all-red intervals to meet the needs of traffic and assess the long-term effectiveness of increasing yellow time on red-light running and crash risk. Observational field studies should be carried out to determine reaction times during onset of the yellow light and develop updated functions for probability of cars stopping versus deceleration required to stop and new functions for trucks. Before-and-after crash studies should be done at intersection where yellow times have been altered. The research task should address questions such as: Do reductions in red-light running associated with increased yellow time translate in to crash reductions? Should yellow timing be based on prevailing speed or posted speed. If prevailing speed is used, should it be 85th percentile, 95th percentile, or some other measure? Does acceptable level of deceleration vary with approach speed and vehicle type? What reaction time is normal? Does reaction time differ by area type or driver age? Should there be an upper limit on length of the yellow? What amount of side street start-up delay if any should be subtracted from the clearance time to determine the amount of all-red? What is a fair and reasonable tolerance for RLC violations? There are approximately 1,000 fatalities and 90,000 injuries each year attributed to red-light running. Deficient yellow times entrap drivers into running red lights or stopping abruptly and risk being rear-ended. Red light cameras are being implemented with little or no grace period. Such practice fails to recognize that current practice for timing yellow lights reflect an average driver and unfairly penalizes a large number of motorists behaving reasonably. Over time, this practice could lead to a backlash against red-light cameras and prohibition of a potentially useful tool in improving highway safety Data collected at several red-light camera (RLC) sites in northern Virginia where the yellow was increased has yielded impressive results and suggests that increasing the yellow interval can be more effective in reducing red-light running than RLCs. The dramatic reductions in red-light running from increasing the yellow have been sustained up to 3 years after the yellow was increased, and there is no evidence that motorists take advantage of the increased yellow over time. Further, it is very simple and inexpensive to implement. This needs to be evaluated on a wider scale and the results widely disseminated. </span><span>The final report should include recommended changes to the <em>Manual on Uniform Traffic Control Devices</em> and a recommended practice for consideration by the Institute of Transportation Engineers. </span></font></div><div><font size="3"> </font></div>


  • English


  • Status: Active
  • Contract Numbers:

    Project 3-95

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  USA  20590

    American Association of State Highway & Transportation Officials

    444 North Capitol Street, NW, Suite 225
    Washington, DC    20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  USA  20001
  • Project Managers:

    Reynaud, David

  • Performing Organizations:

    Vanasse Hangen Brustlin, Incorporated

    P.O. Box 9151, 101 Walnut Street
    Watertown, MA  USA  02471-9151
  • Principal Investigators:

    McGee, Hugh

  • Start Date: 20090318
  • Actual Completion Date: 20110617
  • Source Data: RiP Project 17861

Subject/Index Terms

Filing Info

  • Accession Number: 01464493
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 3-95
  • Files: TRB, RiP, USDOT
  • Created Date: Jan 3 2013 2:43PM