Using GIS to develop a performance-based framework for evaluating urban design and crash incidence

Although traffic safety is a concern to many urban residents, the role of urban design on crash incidence is typically not considered as part of the transportation planning and design process. Much of the problem stems from the types of performance measures used to analyze traffic safety; most conventional safety analyses focus either on crash performance at high crash, ‘black spot’ locations, or else examine safety at the aggregate scale of the city of metropolitan region. Such approaches not only fail to consider how urban design may influence crash incidence, they fail to provide a framework through which the safety effects of urban design can be understood. Urban design influences the composition and distribution of traffic through a community, establishes locations where different users interact and influences the speeds at which these interactions occur. The effects of such factors are experienced neither at the level of the individual intersection, nor at the level of the region. Such effects are best understood at the level of the individual community. To better account for the effects of urban design on crash incidence, the authors recently sought to develop a geographic information systems (GIS)-based database of crash incidence and urban form for the City of San Antonio, Texas. This article details how GIS may be used to analyze the relationship between urban form and crash incidence at the level of the individual community, including the data sources available for creating such a database, strategies for assembling these data using GIS and opportunities for using such databases to advance professional practice. It is hoped that the methods and techniques detailed in this article will assist planners and urban designers in systematically evaluating the effects of community design on traffic safety.