FINAL REPORT
DEVELOPMENT OF LEFT-TURN LANE
guidelines FOR SIGNALIZED AND UNSIGNALIZED INTERSECTIONS
Vijayendra R. Lakkundi
Graduate Research Assistant
Brian Park, Ph.D.
Faculty Research Scientist
and
Research Assistant Professor of
Civil Engineering Nicholas J. Garber, Ph.D., P.E.
Faculty Research Engineer
and
Professor of Civil
Engineering Michael D. Fontaine, P.E.
Research Scientist
Virginia Transportation Research Council
(A Cooperative Organization Sponsored Jointly by the
Virginia Department of Transportation and
the University of Virginia)
In Cooperation with the U.S. Department of Transportation
Federal Highway Administration
Charlottesville, Virginia
March 2004
VTRC 04-R11
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DISCLAIMER
The contents of this report reflect the views of the authors, who are responsible for the
facts and the accuracy of the data presented herein. The contents do not necessarily reflect the
official views or policies of the Virginia Department of Transportation, the Commonwealth
Transportation Board, or the Federal Highway Administration. This report does not constitute a
standard, specification, or regulation.
Copyright 2004 by the Commonwealth of Virginia.
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ABSTRACT
It is generally accepted that the level of service (LOS) at intersections significantly
affects the overall LOS of the road system. It is also known that the LOS at an intersection can
be adversely affected by frequently allowing left-turning vehicles to block through traffic. In
addition, crash rates tend to be higher at intersections than on through sections of a road. The
separation of left-turning vehicles from through traffic is therefore an important condition for the
safe and effective operation of intersections.
Existing guidelines for installing left-turn lanes have several limitations. They are mainly
based on the traffic volumes at the intersection, and they use deterministic models with fixed gap
acceptance and/or left-turn maneuver times. In addition, the guidelines for left-turn lanes for
unsignalized intersections and signalized intersections must be specific for the type of
intersection.
In this study, new left-turn guidelines for both unsignalized and signalized intersections
were developed on the basis of well-validated event-based simulation programs. Guidelines for
unsignalized intersections were based on the percentage of left turns blocking through vehicles,
whereas the guidelines for signalized intersections were developed using a minimum left-turn
volume of either 85% left-turn capacity or LOS E delay (55 seconds/vehicle). In addition to the
general guidelines, a prioritization tool that can be used to prioritize candidate intersections was
developed. The prioritization tool accounts for both operational and safety aspects.
FINAL REPORT
DEVELOPMENT OF LEFT-TURN LANE GUIDELINES FOR SIGNALIZED
AND UNSIGNALIZED INTERSECTIONS
Vijayendra R. Lakkundi
Graduate Research Assistant
Brian Park, Ph.D.
Research Assistant Professor of Civil Engineering
and
Faculty Research Scientist
Nicholas J. Garber, Ph.D.
Professor of Civil Engineering
and
Faculty Research Scientist
Michael D. Fontaine, P.E.
Research Scientist <
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