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 A previous unpublished sign study provided further evidence that the chosen signs were comprehensible and clear to drivers.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.
Performance data collected during the simulated drives and self-reported questionnaire responses were used to evaluate driver behavior and comprehension of the reversible lane designs and associated signs. Results showed that drivers used both versions of the reversible left-turn lane safely and with frequency high enough to potentially improve throughput during periods of high traffic volume.
The following traffic control measures including signs and symbols were used in this study to encourage driver comfort and proper use of reversible lanes:
- Posting advance guide signs describing reversible-lane operations upstream of an intersection.
- Altering stop bars (e.g., raising, embedding, or milling the footprint) to make them visible only to non-reversible traffic.
- Installing low-profile raised curbs or flexible delineator posts along reversible lane markings to discourage lane changes.