Volume Warrants for Left-Turn Storage Lanes at Unsignalized Grade Intersections

• Authored by:  M. Harmelink

Harmelink, M. D. “Volume Warrants for Left-Turn Storage Lanes at Unsignalized Grade Intersections,” Highway Research Record, No. 211, Highway Research Board, National Research Council, Washington, D.C. (1967), pp. 1-18.

The research presented in this paper has been the basis for turn lane warrants and design guidelines across the nation for more than four decades. Harmelink used queuing theory, which is based on gap acceptance and driver delay for left-turning vehicles, to develop left-turn lane warrants for unsignalized intersections on two-lane and four-lane highways. The warrants consider through and right-turn volumes in both directions of travel, roadway speed, and the ratio (percentage) of left-turning vehicles to through vehicles. In addition to providing guidance on when left-turn lanes are warranted, information on recommended storage lengths is also included. While the warrants developed by Harmelink are still used today, more recent research efforts have developed methodologies that also consider the operational effects of turning traffic on through traffic, and most implementations of Harmelink’s warrants have been modified to include these considerations.

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