Modeling Passing Behavior on Two-Lane Rural Highways: Evaluating Crash Risk Under Different Geometric Configurations
Dyre, Brian P.
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Passing maneuvers on rural two-lane highways are a complex task with a significant effect on safety, capacity, and service quality. This maneuver, which involves driving in the lane of the opposing traffic, is associated with simultaneously increasing crash risk and increasing the driver's speed. Understanding drivers' passing behaviors and their decision-making on two-lane rural highways can significantly contribute to accurately predicting risk and service quality. Only limited research has been conducted to capture and document drivers' perception of when they need to pass and passing decision-making. This is partly because it is difficult to collect detailed data on driver perceptions and passing behavior in the real-world environment. Furthermore, field studies offer little control over the intervening variables, and usually no information on the drivers being observed. Evidence showing the effects of this limited research lies in recent work assessing passing sight distance (PSD) standards for two-lane highways in two preeminent manuals. One is the American Association of State Highway and Transportation Officials (AASHTO) Green Book, which states minimum PSD and the other is the Manual on Uniform Traffic Control Devices (MUTCD). Marking of passing and no-passing zones is based on PSD criteria presented in the MUTCD. The National Highway Cooperative Highway Research Program (NCHRP) Report 605 presented recommendations regarding current procedures and guidelines used to estimate minimum PSD requirements for highway design and pavement marking. The report concluded that the MUTCD PSD criteria for marking passing and no-passing zones should also be used for PSD design. It also concluded that although the longer AASHTO PSD criteria might provide improved traffic operational efficiency, the AASHTO PSD are so long they are often impractical. As a result of the report recommendations, the PSD values in the 2011 AASHTO Green Book were modified and brought closer to the MUTCD PSD values. The field data used to validate different PSD models in NCHRP 605 were based on video data collection. Videos were used to study distance traveled by the passing vehicle in the opposing lane, the speed differential between the passed and passing vehicles, and the deceleration rate used by the passing vehicle when the passing maneuver was aborted. No relationship was established between driver perception of quality of service, passing behavior, and the present highway conditions. Finally, the only tool available for estimating two-lane highway performance resides in the Highway Capacity Manual (HCM). This tool is not based on any relationship between observed user perception, documented driver passing behavior, and two lane highway conditions. As a result, the Transportation Research Board's Committee on Highway Capacity and Quality of Service identified researching two-lane highway traffic operations as a high priority research subject, as did the AASHTO.