While the prevailing assumption is that "livable"; street treatments, such as street trees, on-street parking, narrower lanes, and adjacent roadside development, have a negative impact on transportation safety, empirical evidence indicates that these designs are actually safer than conventional roadway designs. In analyzing crash data for several livable and comparable sections of roadway, livable sections had fewer ﬁxed-object, multiple vehicle, and pedestrian crashes as well as fewer injuries and fatalities.
Dumbaugh, Eric. (2005). Safe Streets, Livable Streets. Journal of the American Planning Association 71(3), 283-300.