Abstract
In 2009, NCHRP Project 03–95 sought to develop a comprehensive, uniform set of recommended guidelines for determining safe and operationally efficient yellow change and red clearance (i.e., all-red) intervals at signalized intersections. Before guideline development, a comprehensive field study of driver behavior was performed to establish the three primary parameters found in a commonly used kinematic equation (the ITE equation): perception–reaction time, deceleration rate, and approach speed. To provide broad nationwide representation of driver characteristics, site conditions, and traffic signal timing practices, 83 study approaches were evenly selected from four regions of the United States: Southeast Michigan, Central Florida, Southern California, and Greater Washington, D.C. Driver behavior data were collected at each site with an elevated high-definition video camera. The resulting data set included 2,458 first-to-stop dilemma zone vehicles that were less than 5.5 s upstream of the intersection at the start of the yellow interval. The study's overall mean brake response time of 1.00 s was identical to ITE's recommended default value of 1.0 s for timing of the yellow interval, and the overall mean deceleration rate of 10.08 ft/s2 was very close to ITE's recommended deceleration rate of 10 ft/s2. The study determined that the 85th percentile speed of free-flowing through-moving vehicles approaching a signalized intersection may be accurately estimated by adding 7 miles per hour (mph) to the posted speed limit on the approach. Similarly, the 85th percentile approach speed for free-flowing left-turning vehicles may be accurately estimated by subtracting 5 mph from the posted speed limit.
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