EVALUATION OF AASHTO RULES FOR IMPLEMENTATION OF CLIMBING LANES ON TWO-LANE HIGHWAYS

Lack of passing opportunities, due to limited sight distance and heavy oncoming traffic volumes in dense platoons, results in traffic operational issues on two-lane highways. Climbing lanes extend an opportunity for breaking traffic platoons on two-lane highway upgrades, thus potentially improving traffic operations on these segments. The American Association of State Highway and Transportation Officials promulgates guidelines to implement climbing lanes on two-lane highways that have remained unchanged over its last four editions of ”A policy on Geometric Design of Highways and Streets”. The guidelines do not account for the combination of variables known to determine specifically performance on two-lane highways by the current state-of-the-practice, in particular the opposing flow or the percentage of no-passing zone. Most state Departments of Transportation base their implementation decisions on climbing lanes on these old guidelines. They either refer to the AASHTO guidelines or interpret those directly as warrants. This research study evaluates the efficacy of the guidelines in the face of new research results on two-lane highway performance. The research deploys the Highway Capacity Software to evaluate the performance achieved with and without climbing lanes for two-lane highways for varied scenarios with randomly generated input values. The data serves to contrast the AASHTO recommendations for implementing climbing lanes with their necessity and sufficiency, thereby assessing their sampled efficacy. AASHTO recommendations only prove beneficial for 36% of the scenarios analyzed. Although certain study limitations apply, results point to a need to further research the study theme and potentially update the AASHTO guidelines.