Abstract
The use of an appropriate method in determining the left-turn signal change interval (yellow change interval plus red clearance interval) can result in signal timings that improve both safety and efficiency of an intersection. An improved framework for calculating the change interval for the left-turn movement is presented: it incorporates a comprehensive set of parameters, which are identified from a survey. Field data collected from 21 intersections in eight Texas cities were used for the basic calibration of three essential parameters within the improved framework: drivers’ entering driving behavior, drivers’ behavior on left-turn curves, and drivers’ tolerable centrifugal force. After the basic calibration, a sensitivity analysis of the three essential parameters was conducted. Further, a systematic calibration approach was designed to extend the improved framework to a wider range of intersections with different approach speed limits, number of left-turn lanes, control types, and truck percentages. Values of the three essential parameters under different intersection attributes were calculated; they can be of direct reference for practicing engineers. Finally, the effect of intersection attributes on the yellow change and red clearance intervals was analyzed. The research recommends that the change intervals for left turns based on the proposed framework and calibration method be used by practicing engineers, which would improve both safety and efficiency of the intersection.