Greater sprawl leads to a higher pedestrian death rate -- not jusr fewer people out walking. From the New York Times:
Urban sprawl comes with numerous liabilities, among them, as it happens, a heightened risk of pedestrian death, which may not seem entirely obvious given that you are infinitely more likely to see people walking around Manhattan than you are to see people walking around Atlanta. Data in a coming report from the National Institutes of Health indicate that for every 1 percent increase in a city’s compactness index, essentially a measure of its density, there is a 1.9 percent drop in the pedestrian fatality rate, adjusted for exposure. The more miles traveled by car in a particular place, the greater the chance of accident, as Reid Ewing, the report’s lead researcher and a professor of city and metropolitan planning at the University of Utah, said.