Left-turn Lane Installation Guidelines

• Authored by:  Kay Fitzpatrick
• Co-authored by:  T. Wolff

Fitzpatrick, K. and T. Wolff, “Left-turn Lane Installation Guidelines,” Proceedings of the 2nd Urban Street Symposium, Transportation Research Board, Anaheim, California (2003)

This report summarizes several previous research efforts focusing on criteria for the installation of left-turn lanes at intersections. The goal of this report was to streamline previous research efforts into a single set of guidelines that included considerations for delay, safety, and conflict avoidance. After reviewing eight different techniques for evaluating left-turn lane installations, as well as the guidelines adopted by several DOT agencies across the nation, the authors developed their own comprehensive guidelines based on the strongest components of each previous research effort. In addition to combining the different methods into one set of criteria, the authors suggest making adjustments to several base line assumptions, such as increasing the critical gap from 5.0 seconds to 5.5 seconds, increasing the time to make a left-turn from 3.0 seconds to 4.3 seconds, and increasing the time to clear the lane from 1.9 seconds to 3.0 seconds.