rhubarbquid parent
I've heard both that you should not answer for fear of incriminating yourself, and that you should answer because not knowing how fast you're going means you're negligent and that's also a crime. (I'm neither a lawyer nor know which is the better choice)
IANAL, but the way I've had it described to me is not knowing exactly how fast you're going is not negligence, as it's always a better idea to keep your eyes on the road instead of a speedometer. Hitting people is a potentially more serious crime than speeding. I'd love to hear a lawyer's take on this, however.