Momentum matters as much as speed. Suppose you are doing 35mph on a bike the road and you get sideswiped by a car doing 35mph. The direct impact is negligible,

Momentum matters as much as speed. Suppose you are doing 35mph on a bike the road and you get sideswiped by a car doing 35mph. The direct impact is negligible, but now you've got angular momentum that is going to send you into another car or the ground at high speed. And even if you are doing 35mph, and claiming a lane, you'll still be passed (often unsafely) by cars doing 40, 50mph. (Source: motorcyclist who can't go fast up hills)