I thought it was 4 Hz strobe that cause epileptic seizures. But I have never heard of anyone having a seizure from a film. And I agree... if the authorities cannot assure that the speed limit will not cause flashing sunlight that may cause seizures.... htey really ARE obligated to post signs. But they should also feel obligated to post signs that say, "Driving slower than speed limit is just as unsafe as driving too much faster than the speed limit."