Planetizen links to a New Urban News article reporting on a study which finds that cities built in California before 1950 have safer raods than those built after 1950. The authors, Wes Marshall and Norman Garrick, find that post 1950 cities:

tend to have more “dendritic” networks — branching, tree-like organizations that include many cul-de-sacs, limiting the movement of traffic through residential areas. They also don’t have as many intersections.

They suggest these “dendric” networks actually lead to greater travel speeds which in turn cause more fatalities. “Connected” grid-like streets are less likely to lead to fatal accidents because the heavier traffic leads to lower travel speeds.