Safe Urban Form: Revisiting the Relationship Between Community Design and Traffic Safety

Problem: While concerns about traffic safety were central to the development of conventional community design practice, there has been little empirical examination of the relationship between community design and the incidence of traffic-related crashes, injuries, and deaths. Purpose: We examine the relationship between community design and crash incidence. Methods: We present a brief historical review of the safety considerations that helped shape conventional community design practice and then analyze GIS data on crash incidence and urban form using negative binomial models. Results and conclusions: We find that many of the safety assumptions embedded in contemporary community design practice are not substantiated by the empirical evidence. While disconnecting local street networks and relocating nonresidential uses to arterial thoroughfares can reduce neighborhood traffic volumes, this does not appear to improve safety, but rather substitutes one set of safety problems for another. We found urban arterials, arterial-oriented commercial developments, and big box stores to be associated with increased incidences of traffic-related crashes and injuries, while higher-density communities with more traditional, pedestrian-scaled retail configurations were associated with fewer crashes. We found intersections to have mixed effects on crash incidence. We conclude by discussing the likely reasons for these findings (vehicle operating speeds and systematic design error) and outline three community design strategies that may help improve traffic safety. Takeaway for practice: Community design is strongly associated with crash incidence. The speed and operating characteristics of arterial thoroughfares, as well as the design and configuration of commercial and retail uses, appear to be particularly important. Our findings suggest that safety may be enhanced by strictly managing access along arterial thoroughfares and by locating commercial and retail uses away from these roadways, or at least orienting them toward lower-speed access lanes with limited connections to the arterial system. Designing communities to have higher-density, more urban design configurations generally appears to help reduce crash incidence, although four-leg intersections pose potential traffic hazards.