Death by sprawl: traffic fatalities associated with land use patterns of sprawl

Reid Ewing & Shima Hamidi & James Grace, "Urban sprawl as a risk factor in motor vehicle crashes," Urban Studies 53 (2016): 2

The take-away: This statistical study investigates the relationship between sprawl and motor vehicle crashes. The findings indicate that sprawl both directly and indirectly causes higher traffic fatality rates. The authors suggest this may be because areas characterized by sprawl feature higher VMT, higher speeds, and slower emergency response times.

Abstract: A decade ago, compactness/sprawl indices were developed for metropolitan areas and  counties which have been widely used in health and other research. In this study, we first update the original county index to 2010, then develop a refined index that accounts for more relevant factors, and finally seek to test the relationship between sprawl and traffic  crash rates using structural equation modelling. Controlling for covariates, we Mind that sprawl is associated with significantly higher direct and indirect effects on fatal crash rates.  The direct effect is likely due to the higher traffic speeds in sprawling areas, and the indirect effect is due to greater vehicle miles driven in such areas. Conversely, sprawl has negative direct relationships with total crashes and non-fatal injury crashes, and these offset (and sometimes overwhelm) the positive indirect effects of sprawl on both types of crashes through the mediating effect of increased vehicle miles driven. The most likely explanation is the greater prevalence of fender benders and other minor accidents in the low speed, high conflict traffic environments of compact areas, negating the lower vehicle miles travelled per capita in such areas.

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