[UnFleshedOne]

Might have something to do with the size of your signature (I think that's what they call it in military terms).

Consider a spherical traveler following a certain path in a field of randomly moving projectiles. The chances of being hit with one depends on path length, your own size, and how long you stay on the field.

Seriousness of the hit depends on your durability and speeds involved.

Maybe pedestrians just spend a lot of time exposed (assuming they have to cover similar distance) and bikers are extra fragile.