Pedestrian/Bicyclist Safety in Numbers: Program Evaluation [Traffic Tech]

NHTSA · 2022 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration. Office of Behavioral Safety Research

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Summary

This paper evaluates the "Safety in Numbers" (SIN) hypothesis, which posits an inverse relationship between the volume of pedestrians and bicyclists and their individual crash risk. Motivated by a 38% increase in bicyclist fatalities and a 46% increase in pedestrian fatalities between 2011 and 2020, the study investigates whether programs designed to increase non-motorized travel volumes demonstrably reduce crash probabilities. The research aims to clarify conflicting literature regarding whether increased exposure leads to safer outcomes or heightened risk. The study employed a comparative evaluation across three sites: Fort Collins, Colorado; Philadelphia, Pennsylvania; and Anchorage, Alaska. Researchers analyzed specific local initiatives, including Fort Collins’ Safe Routes to School and Open Streets events, Philadelphia’s Indego Bikeshare Initiative, and Anchorage’s Bikeology program. The methodology involved acquiring and processing diverse datasets, including program metrics, crash records, and traffic volumes. Data preparation included converting short-term counts to annual averages, geocoding locations, and defining crash zones. Statistical models, including Poisson, negative binomial, and zero-inflated variations, were used to assess program effectiveness in increasing volumes and to quantify SIN effects. An ad-hoc analysis also examined the role of infrastructure by coding 17 facility types in Philadelphia. Results regarding program effectiveness were mixed. The Philadelphia bikeshare program successfully increased bicyclist volumes but had no effect on pedestrian volumes. Fort Collins results were unclear due to data quality and program nature issues, while Anchorage lacked sufficient data for analysis. Regarding SIN, Fort Collins and Anchorage exhibited "complete" SIN for bicyclists and "partial" SIN for pedestrians, meaning crash rates increased less than proportionally to volume increases. Philadelphia showed no evidence of SIN. The infrastructure analysis yielded counterintuitive findings: standard and high-visibility crosswalks were associated with higher bicyclist crash rates, and pedestrian signals with higher pedestrian crash rates, likely due to increased exposure and volumes at these locations. The study concludes that while SIN may offer insights into the outcomes of increasing non-motorized travel, it does not guarantee safety improvements without systemic changes. As volumes rise, absolute crashes and injuries are likely to increase, even if the rate of increase is lower than the volume growth. The authors emphasize that current research identifies correlations rather than causation, noting significant data gaps in infrastructure and behavioral factors. They caution practitioners that relying solely on SIN to justify policies may overlook the need for comprehensive safety measures, such as those found in Vision Zero initiatives, to mitigate the inherent risks of increased exposure.

Key finding

Complete Safety in Numbers effects were observed for bicyclists and partial effects for pedestrians in Fort Collins and Anchorage, while no such effect was found in Philadelphia.

Methodology

dataset

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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• cyclist safety
• incidence prevalence
• vru crash typology

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).

• Applied Guidance: countermeasure evaluation
• Empirical Findings: crash risk outcomes