A recent US study into the affect of community design on traffic safety is reported in the new issue of the Journal of the American Planning Association. Results include finding a 6.6% increase in total crash incidence for each big box store located adjacent to an arterial thoroughfare and a 2.2% decrease in crash incidence for each pedestrian-scaled commercial or retail use. Population density increases were associated with fewer crashes. Each additional mile of arterial roadway within a block group was associated with a 15% higher incidence of crashes.
Traffic Safety and Community Design: What is the Relationship?
The Journal of the American Planning Association (JAPA) article Safe Urban Form: Revisiting the Relationship Between Community Design and Traffic Safety looks at how the design of our communities may lead to traffic crashes, injuries, and deaths.
The article, published in the Summer issue, analyses three years of traffic accident data for the City of
One of its most important conclusions is that many current assumptions about how community design practice affects traffic safety are not supported by empirical evidence. The article reviews the connection between traffic safety and community design practices since the beginning of the 20th century, including:
- Arterial thoroughfares
- Routing traffic away from residential zones
- Reducing numbers of four-way intersections
- Disconnected residential subdivisions and cul-de-sacs
- Retail and commercial uses located on arterial roads designed for heavy traffic volumes
The study matched data on crash incidence at the block group level 4 in the City of San Antonio (a city of 1.4 million residents) with data on land use, street network characteristics, traffic volumes, and community demographics, and then analysed them using a series of negative binomial regression models 5 to predict the incidence of total, injurious and fatal crashes.
Results include finding a 6.6% increase in total crash incidence for each big box store located adjacent to an arterial thoroughfare and a 2.2% decrease in crash incidence for each pedestrian-scaled commercial or retail use. Population density increases were associated with fewer crashes. Each additional mile of arterial roadway within a block group was associated with a 15% higher incidence of crashes.
The authors note that the speed of modern vehicles makes urban arterials 6 particularly problematic. Though they are designed to address regional mobility functions 7, they are also commonly shopping corridors. When asked about these findings, Dumbaugh replied, “from a traffic safety perspective, the modern commercial arterial is a perfect storm of bad planning and design. These roads are designed to support high operating speeds, making it difficult for drivers to stop quickly to avoid a crash, and the presence of commercial and retail uses on these roads means that drivers will routinely need to stop quickly in order to avoid crashing into pedestrians, bicyclists, and especially vehicles turning in and out of driveways.”
While the presence of big box stores and strip commercial uses led to significant increases in crash incidence, the presence of more urban, pedestrian-oriented retail configurations was associated with a significant reduction in traffic crashes, a finding which helps illustrate the role of design. “We’re seeing this in a growing number of studies, both here in the
Based upon the data obtained and the results, the authors make three suggestions for future design enhancements to roads and communities: manage mobility and access functions of urban arterials; relocate retail and commercial uses to lower-speed thoroughfares (or reduce speeds on roads already lined with commercial uses); and give greater attention to how land use planning may affect crash incidence. The article concludes that the relationship between community design and traffic safety are very important, and calls for a more thoughtful, evidence-based approach to addressing traffic safety through community design.