There is some evidence concerning the incidence of accidents involving trams in Sheffield, although most of the studies appear to date back to the early years of the tram system.
When the system first started, there was concern about the number of accidents involving cyclists and pedestrians. Indeed, there are learned papers by Sheffield medical staff on this very issue. This was compounded by a number of well-publicised accidents involving cars and the tram system (either through skidding on the track or through collisions).
I give some examples of this evidence below, although I would be interested to see more recent data.