United States Department of Transportation
i
Development of guidelines for triple left and dual right-turn lanes : technical report.
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2011-07-01
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[PDF-5.17 MB]
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Alternative Title:Project title: Development of guidelines for triple left and dual right-turn lanes
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Edition:Technical report; Sept. 2008-Aug. 2010.
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Abstract:Left- or right-turn lanes at intersections improve safety and operations by separating turning and through vehicles. At intersections
with heavy turning demand, it may be necessary to provide multiple turn lanes. Triple left-turn (TLT) and dual right-turn (DRT)
lanes are still considered as relatively new designs that many agencies are reluctant to use, so they are somewhat limited in Texas.
Guidelines for TLT or DRT lanes are almost nonexistent, leaving traffic engineers to rely on judgment for their designs. Therefore,
this research was needed to develop consistent guidance. The 0-6112 project achieved two primary project goals: (1) development
of geometric and signal design guidelines for TLT and DRT lanes; and (2) evaluation of the safety and operational performance of
TLT and DRT sites in Texas.
Researchers conducted field studies at 5 TLT and 20 DRT, primarily in the Dallas-Fort Worth and Houston urban areas, in order to
evaluate lane utilization patterns, saturation flow rates, conflicts, and other operational factors. The research team also analyzed
safety performance by investigating the crash history of the 25 sites using three techniques: collision diagrams, field conflict study,
and comparison study. The results revealed that TLT lanes do not experience any major safety issues and also concluded that, in
general, a well-designed DRT lane does not cause significantly higher crash frequency or severity compared to single right-turn
lanes.
Based on the results of this research and the geometric and signal design guidelines, TxDOT and other agencies should be
confident that well-designed TLT and DRT lanes can be implemented to address heavy turning demand at key intersections. The
evaluation of these multiple turn lane sites in Texas revealed that they perform well from both operational and safety standpoints.
TLT and DRT lanes are not appropriate for all situations, and their use should be supported by an operational analysis. Other
techniques (grade separation, signal timing, etc.) might be better solutions for a particular site, especially when considering the
effects of adjacent intersections, pedestrian/bicycle movements, and other key factors. Researchers developed a product, Keys to
Successful Public Outreach, which is useful for implementing multiple turn lane projects.
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