Actually neither of those matter much anyway. The energy transferred is primarily a function of the velocity difference (squared) and the mass of the lighter o

Actually neither of those matter much anyway. The energy transferred is primarily a function of the velocity difference (squared) and the mass of the lighter of the two objects. That is, a pedestrian will experience a collision with a car and with a bus in much the same way. If the two objects are close to the same mass, i.e. car vs. car, the energy transfer will be reduced by up to 75%, but otherwise the mass of the larger object is immaterial. That is, a car-car collision at 60 MPH does equal damage as a bus-car collision at 30 MPH.