And "black box" evidence might just as well make for a quick judgment in favor of the defendant. How long does a trial last when all you have are people making contradictory claims? It becomes a long, drawn out crap shoot.
A black box can help settle the issue in no time, for or against.
but since such a large percentage of people exceed the posted speed limit (since they are set artificially low on most roads) - most people are going to be shown in violation based on the black box.