Passing Zone Behavior and Sight Distance on Rural Highways: Evaluation of Crash Risk and Safety under Different Geometric Conditions

Belz, Nathan; Chang, Kevin · 2018 · ROSA P / Pacific Northwest Transportation Consortium (PacTrans) (UTC)

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Summary

This study evaluates how horizontal curvature, vertical curvature, and guardrails influence driver passing behavior and crash risk on rural two-lane highways. The research was motivated by the high fatality rate associated with passing maneuvers on rural roads, particularly on curves, and the need to assess whether current American Association of State Highway Transportation Officials (AASHTO) and Manual on Uniform Traffic Control Devices (MUTCD) design standards accurately reflect real-world driver behavior. Specifically, the authors sought to determine if geometric conditions and roadside features affect passing choices, maneuver characteristics, and safety outcomes. The methodology combined field data collection with a controlled driving simulator experiment. Field data were gathered via video recording at three highway segments in Alaska: Parks, Seward, and Sterling Highways. A total of 165 hours of video were analyzed to observe real-world passing maneuvers. These field observations informed the development of a driving simulator environment that replicated the specific geometric alignments of these highways. Seventy-two participants were recruited to drive in the simulator, allowing researchers to isolate the effects of horizontal and vertical curvature and the presence of guardrails on passing behavior without the confounding variables present in naturalistic driving. Field results revealed that passing vehicles traveled approximately 10 mph over the posted speed limit, while vehicles being passed traveled about 2 mph over the limit, contradicting AASHTO assumptions that passing speeds do not exceed the limit. The study also identified a significant prevalence of "early start" and "late finish" passes, where maneuvers extended beyond designated passing zones, occupying the opposing lane for longer durations than compliant passes. Simulator results demonstrated that both horizontal and vertical curvature significantly affected passing maneuver characteristics, including passing vehicle speed, total time and distance of the maneuver, and the distance between vehicles at initiation and termination. However, geometry did not significantly affect safety outcomes in terms of time to collision. Regarding guardrails, their presence did not alter the frequency of passes or collision safety metrics but did impact drivers' ability to avoid collisions when another vehicle was in their lane. The findings suggest that current design standards may underestimate the speeds and spatial requirements of actual passing maneuvers. While geometric curvature influences how drivers execute passes, it does not inherently change the safety outcome regarding collision time. The study concludes that guardrails may negatively impact safety by converting potential run-off-road crashes into more severe head-on collisions, suggesting that additional safety precautions, such as specific signage, may be warranted in areas with guardrails. These insights provide state Departments of Transportation with improved criteria for designing and evaluating geometric roadway configurations to enhance traffic safety and operational efficiency.

Key finding

Guardrails do not affect the number of passing maneuvers or overall safety outcomes but significantly reduce drivers' ability to avoid collisions when another vehicle is in their lane.

Methodology

mixed_methods

Sample size: 72

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).

Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• rail grade crossings
• road geometry
• perceptual countermeasures
• urban rural setting

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Empirical Findings: crash risk outcomes, behavioral performance data
• Methodological Resource: dataset resource