Pedestrian/Bicyclist Safety in Numbers Program Evaluation

Jackson, Steve; Miller, Sheryl; Goughnour, Elissa; Boller, Nadia; Johnson, Kristie; Kehoe, Nicholas; Symoun, Jennifer · 2022 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration. Office of Behavioral Safety Research

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Summary

This report evaluates the "Safety in Numbers" (SIN) hypothesis, which posits an inverse relationship between the volume of walking/bicycling and the probability of motorist collisions with pedestrians or bicyclists. Motivated by rising pedestrian and bicyclist fatalities in urban areas and a prior literature review confirming the existence of SIN effects, the study aimed to determine if specific programs designed to increase non-motorized travel could demonstrate these safety benefits. The research team selected three cities—Fort Collins, Colorado; Philadelphia, Pennsylvania; and Anchorage, Alaska—based on criteria including climate, geographic diversity, and data availability. The evaluation focused on specific initiatives: Fort Collins’ Safe Routes to School, Open Streets, Bicycle Ambassador Program, and Bike to Work Day; Philadelphia’s Indego Bikeshare Initiative; and Anchorage’s Bikeology program. The methodology involved acquiring and preparing multifaceted datasets, including program participation metrics, crash data, traffic volume counts, and infrastructure details. The team converted short-term counts to annual average daily volumes, geocoded crash locations, and determined appropriate crash zone sizes. Statistical models, specifically negative binomial regression as recommended by Elvik (2013), were used to analyze the relationship between program implementation, volume changes, and crash rates. The analysis distinguished between "complete SIN" (crashes increase less than proportionally to simultaneous increases in non-motorized and motorized volumes) and "partial SIN" (crashes increase less than proportionally to increases in either volume type). Results varied significantly across sites. In Fort Collins, findings were mixed, raising questions about program nature and data quality. In Philadelphia, the bikeshare program positively affected bicyclist volumes but had no effect on pedestrian volumes; notably, no evidence of SIN was found in Philadelphia. However, an ad-hoc analysis incorporating infrastructure data (e.g., bike lanes, sidewalks) yielded statistically significant results for volumes and crash rates. In Anchorage, program data were insufficient for robust analysis, though the available data indicated complete SIN for bicyclists and partial SIN for pedestrians. Fort Collins also showed evidence of complete SIN for bicyclists and partial SIN for pedestrians. The study concludes that robust, multifaceted data are essential for evaluating program effectiveness and SIN, yet such data are challenging to obtain due to limitations in local agency capacity and data collection practices. The research highlights that while SIN effects exist, their manifestation depends on context, including infrastructure quality and data integrity. The findings provide a framework for future researchers, offering solutions to common data challenges and emphasizing the need for comprehensive data collection to accurately assess the safety impacts of walking and biking promotion programs.

Key finding

The Indego Bikeshare Initiative in Philadelphia positively affected bicyclist volumes, while complete Safety in Numbers was observed for bicyclists and partial Safety in Numbers for pedestrians in Fort Collins and Anchorage, though Philadelphia showed no evidence of the effect.

Methodology

field_study

Provenance

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

Topics

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• incidence prevalence
• cyclist safety
• vru crash typology

Information type

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• Applied Guidance: countermeasure evaluation
• Empirical Findings: crash risk outcomes, observational prevalence