CC: http://en.wikipedia.org/wiki/Strict_liability
It's exactly like Oak said above. For traffic cases, it doesn't matter whether or not you knew you were doing X; all a prosecutor would need to prove was that you were doing X:
"Strict liability often applies to vehicular traffic offenses. In a speeding case, for example, whether the defendant knew he or she was exceeding the posted speed limit is irrelevant. The prosecutor would need only prove that the defendant was indeed operating the vehicle in excess of the speed limit."