A car can kill a pedestrian/bicyclist/motorcyclist at surprisingly low speeds. It's almost impossible to kill someone in a car at under 25 MPH or so (unless they drive off a cliff or something), but pedestrians can be killed by cars going as slowly as 10 MPH (they get knocked off their feet and hit their heads, usually). I read a very interesting paper by the NTSB or IIHS about that, but can't find it now.