If a car is traveling 20 mph and hits a pedestrian the pedestrian has a 5% chance of dying. If that same car is traveling 30 mph the pedestrian has an 45% chance of dying. If you're looking for a new home, it might be worth looking on streets that move slowly.
A corollary to this is that if you're traveling 20 mph on your bike and you hit a parked car you might have around a 5% chance of dying, because what matters is the relative speed. But if you're traveling 30 mph your risk might be closer to 45%. Same goes for the snowboarder who hits a tree.