2014 - Research

Bicyclist Safety Performance Functions for a US City

Efforts have intensified to apply a more evidence-based approach to traffic safety. One such effort is the Highway Safety Manual, which provides typical safety performance functions (SPFs) for common road types.

  • SPFs model the mathematical relationship between frequency of crashes and the most significant causal factors.
  • Unfortunately, the manual provides no SPFs for bicyclists, despite disproportionately high fatalities among this group.
  • In this paper, a method for creating city-specific, bicycle SPFs is presented and applied to Boulder, Colorado. This is the first time a bicycle SPF has been created for a U.S. city. Such functions provide a basis for both future investigations into safety treatment efficacy and for prioritizing intersections to better allocate scarce funds for bicycle safety improvements.

Key findings: 

  • As expected, the SPFs show that intersections with higher bicyclist traffic and higher motorist traffic have higher motorist-cyclist collisions.
  • The SPFs also demonstrate that intersections with more cyclists have fewer collisions per cyclist, illustrating that cyclists are safer in numbers.
  • Intersections with fewer than 200 entering cyclists have substantially more collisions per cyclist.

Nordback, K., Marshall, W. E., & Janson, B. N. (2014). Bicyclist safety performance functions for a U.S. city. Accid Anal Prev, 65, 114-122. doi: 10.1016/j.aap.2013.12.016