Using Simulation to Assess Conflicts Between Bicyclists and Right-Turning Vehicles

Christofa, Eleni; Knodler Jr., Michael A.; Deliali, Aikaterini · 2019 · ROSA P / Safety Research Using Simulation (SAFER-SIM) University Transportation Center

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Summary

This study investigates the safety conflicts between bicyclists and right-turning vehicles, specifically focusing on how transitions between separated and mixed-traffic environments affect driver behavior. While protected bike lanes (PBLs) reduce collisions along roadway segments, they may cause drivers to underestimate the presence of bicyclists at intersections, leading to "right-hook" crashes. The research aims to determine if specific combinations of segment-level and intersection-level infrastructure treatments can improve driver situational awareness and scanning behavior. The researchers employed a high-fidelity driving simulator at the University of Massachusetts Amherst to test 32 participants across eight scenarios. These scenarios combined two segment treatments (protected bike lanes and conventional bike lanes) with two intersection designs (protected intersections and non-protected intersections), with and without a bicyclist present on the upstream segment. Data collection included kinematic metrics (speed, acceleration) and eye-tracking to record visual glances. The analysis focused on driver speed and the frequency of rightward glances toward bicyclists or intersection infrastructure during the segment approach and at the intersection zones. Results indicated that both the presence of a bicyclist and the implementation of protected bike lanes significantly reduced average vehicle speeds on the roadway segment. At the intersection, the presence of a bicyclist significantly reduced speed in non-protected intersection designs. Regarding visual behavior, the presence of a bicyclist on the upstream segment significantly increased the likelihood of drivers glancing right at the intersection approach, regardless of the intersection configuration. However, drivers were less likely to glance at the bicyclist while traveling on a segment with protected bike lanes compared to conventional bike lanes. Additionally, protected intersections attracted more driver attention to the infrastructure itself, with approximately 94% of participants glancing at the design elements in protected intersections versus 62% in conventional ones. The findings suggest that while protected bike lanes improve segment safety, they may inadvertently reduce driver scanning for bicyclists during the approach to an intersection. The presence of a visible bicyclist serves as a critical cue that triggers necessary scanning behavior. Protected intersections appear to enhance driver awareness of the infrastructure, potentially compensating for reduced scanning caused by upstream separation. These results provide evidence-based guidance for transportation planners, indicating that combining protected bike lanes with protected intersections may mitigate right-hook conflicts by maintaining driver alertness through distinct visual cues and physical barriers.

Key finding

The presence of a bicyclist significantly reduces intersection speed in non-protected designs and increases right-glancing behavior, while protected bike lanes reduce driver glances at bicyclists on the segment.

Methodology

simulator

Sample size: 32

Provenance

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

Topics

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• cyclist safety
• driver vru interaction
• looked but failed to see

Information type

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• Empirical Findings: behavioral performance data