If you're a motorist at speed (and I'll take "at speed" to mean normal street speed); you're almost probably not looking for a parking spot. Further, if you're going "at speed" --25-35mph -- the person behind you should be, at minimum, 2-3 car lengths behind you. If they aren't, they're failing to maintain a safe distance. You're not liable if the person behind you, driving unsafely, rear-ends you.