quall writes "The Ohio Supreme Court has ruled that police may estimate your car's speed and issue a ticket if they believe you were speeding. The hearing threw out a radar gun as evidence because the officer was not qualified to use it, but apparently his guess was good enough. If you make your way into Ohio, I suggest driving 5mph under the speed limit because this leaves little room to dispute your ticket in court. The only chance you have is if the issuing officer decides to skip your hearing."
I wonder whether the court would also accept a driver's own GPS log as exculpatory evidence.