Passing Segment Length Determination on Two-Lane Highways

Passing lane has been often constructed to dissipate traffic queues growing behind slow moving vehicles. These queues may appear randomly on a two-lane highway depending on geometry, traffic volumes, location and vehicle performance. For example, on the uphill side of a highway with relatively high AADT, a transient queue can rapidly grow behind a slow leading heavy vehicle. Aggressive drivers in the queue, losing patient of coasting along at a low speed, may make unsafe passing maneuver at occasions with limited passing sight distances in the presence of double-yellow centerline. Since passing sight distance may not be sufficient at many spots along a two-lane highway, installing a passing lane becomes necessary to relieve recurrent transient queues and avoid traffic collisions due to passing. The purpose of our study is to determine the passing segment length that is sufficiently long to dissipate the foreseeable traffic queues. Based on the criterion for dissipating a traffic queue behind a slow leading vehicle, we derive the passing length by integrating vehicle performance, driver characteristics, roadway geometry, traffic flow volume, and queue size into one realistic and analytic equation. All parameters introduced into this study can be adjusted for any highway project to fit anticipated design scenarios for enhancing traffic operational safety on two-lane highways. Interesting consequences from this study will be presented to showcase the usefulness of this multi-parameter framework. Practitioners can easily apply this framework to estimate or check the potential project scope and make long-lasting smart decisions for improving safety and operation and potentially reducing emissions on two-lane highways