Comparative Analysis of Leading and Lagging Left Turns: Final Report

This project was undertaken to compare operational and safety characteristics of leading versus lagging protected left turn operation. The measures of effectiveness included field measured intersection delay with leading and with lagging left turns. Intersections in Pima County, Glendale, Tempe and Mesa, Arizona were studied with both leading and lagging operation. Intersection delay studies were also done with first car versus third car actuation of leading protected left turn phases. Signal progression was studied with leading, lagging and combination of leading and lagging left turns which provided the best progression. This evaluation was accomplished with an instrumented vehicle and travel time runs throughout a grid. Accident studies were conducted in Tucson, Pima County and Scottsdale, Arizona. These studies compared accident frequency before and after the conversion from leading to lagging left turns. A public opinion survey was conducted to obtain motorists' preference of leading or lagging left turns.