This post from Grist looks at the study from the University of Virginia, and discusses some of the reasons cities aren't as dangerous as they might seem.
"The study found that the most dangerous regions of nine metropolitan areas (Baltimore, Chicago, Dallas, Houston, Milwaukee, Minneapolis-St. Paul, Philadelphia, and Pittsburgh) are the outer suburbs. (Inner-ring suburbs were the safest, with central cities coming in second.) People, especially children, are most likely to be hurt or killed in an automobile crash, and, not surprisingly, automobile crashes are more prevalent in areas that require cars to get around. (Outer suburbs also tend to be dominated by two-lane roads, which are responsible for roughly 77 percent of automobile fatalities.) Even though the risk of homicide by a stranger (incidentally, a small percentage of all homicides) is slightly higher in central cities, the difference is not enough to overcome the significantly elevated risk in outer suburbs of a fatal car crash."