Evaluation of traffic safety in sprawl and urban growth in California metropolitan areas

Background/Purpose

Motor vehicle crashes are one of the leading causes of fatalities and injuries in United States each year. Recent findings suggest urban sprawl significantly contributes to the high levels of traffic fatalities and injuries. Therefore, we completed a descriptive cross-sectional and time-series analysis on the relationship between urban growth and motor vehicle crashes.

Methods

Fatal and severe injury crashes in the California Statewide Integrated Traffic Records System (SWITRS) were geocoded for Sacramento and Placer counties. The years of 1998 and 2006 were chosen for analysis due to large amounts of population growth in the counties between those years. Geographic Information Systems (GIS) tools were used to map the collisions and create density maps for the counties for each year. Population values and urban growth acreage data was also obtained to relate to collision counts.

Results/Outcomes

In 2006, urban areas have grown outward towards the periphery of the counties and higher crash densities are more dispersed compared to crash patterns in 1998. Accordingly, the percentage increase in traffic fatalities and injuries (35%) are significantly higher than that of population increase (23%) in the same region. Higher collision densities are also concentrated in core urban areas.

Conclusions

We are able to visually show the relationship between urban sprawl and collisions in selected regions during two distinct time periods using GIS. The results should provide insight into how growth patterns affect traffic safety and help inform planning and policy solutions to reduce motor vehicle crashes.