Guidelines for Timing Yellow and Red Intervals at Signalized Intersections

The lack of a national standard, recommended practice, or set of guidelines for determining the duration of the yellow change and red clearance intervals for the timing of traffic signals has left each transportation agency to determine its own practices. The objective of NCHRP Project 03–95 was to develop a comprehensive and uniform set of recommended guidelines for determining safe and operationally efficient yellow and red intervals at signalized intersections. To accomplish this objective, the study established a state of knowledge and a state of practice through a review of existing guidelines and various literature sources and a survey of transportation agency practitioners. The research also conducted a comprehensive national investigation of driver behavioral characteristics through an extensive field data collection and analysis effort. These efforts confirmed the accepted values for perception–reaction time (1.0 s) and deceleration rate (10 ft/s2) and established 85th percentile speed estimations for through and left-turning vehicles. Justification was also provided for accounting for start-up delay. From the findings, a succinct recommended guideline for the timing of yellow change and red clearance intervals was formulated on the basis of a kinematic equation and its associated variable values. The recommended guideline encourages a uniform practical application that provides a framework that can be easily adopted into transportation agency practice.