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Throughput at signalized intersections with high left-turn demand is a common cause of bottleneck for traffic flow. Dynamic lane-grouping strategies offer cost-effective methods for increasing operational efficiency within existing rights of way. Previous traffic simulations suggest that reversible left-turn lanes can significantly increase throughput at intersections where left-turn demand is high. However, the operational benefits offered by reversible-turn-lane designs depend on safe and proper use by drivers.

Because reversible lanes make use of existing infrastructure and are time-of-day dependent, they require clear and adaptive signs and signals to indicate the active or closed status of a reversible lane and control alternative lane assignment during active periods. Reversible-lane designs may also expose drivers to novel or unfamiliar situations, such as sharing a lane with opposing traffic waiting at the far side of the intersection. In these cases, appropriate signs can mitigate unsafe driving behaviors and driver discomfort or confusion. In addition, improved signs and markings may aid in minimizing issues observed at existing reversible-lane interchanges, such as incorrect or missed turns and lane changes within the intersection.

Two experiments were conducted in a highway driving simulator to evaluate driver behavior and sign comprehension during reversible-lane operations compared to conventional-lane operations. Several key behaviors were measured to evaluate safe and efficient use of reversible-lane interchanges, including lane choice, sign comprehension, and appropriate navigation of reversible lanes. Conventional versions of the interchanges were simulated to provide a basis of comparison for driving performance. The signs used in these studies were chosen based on feedback obtained from a panel of subject-matter experts. A previous unpublished sign study provided further evidence that the chosen signs were comprehensible and clear to drivers.

The experiments tested the dynamic reversible left-turn (DRLT) lane at diamond interchanges and the contraflow left-turn (CLT) lane at signalized intersections. The DRLT lane design replaces back-to-back left-turn lanes with reversible lanes that span the entire distance between interchange nodes. In a CLT lane intersection, a gap in the median allows drivers turning left to queue in a lane that is normally used by opposing through traffic. This design provides an additional left-turn lane without widening the roadway.
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U.S. DOT Federal Highway Administration
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Simulator Assessment of Alternative Lane Grouping At Signalized Intersections
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