I call bullshit.
It would have been more convincing had the guy not said, "I'm going twice the speed limit. I'm going to burn this stop sign, and see if he stops me." Then thirty seconds later the cop says, "You're looking for a gas station? Is that why you burned the stop sign, at twice the speed limit?"
It might NOT have been scripted, but what are the chances of two people using two nearly exactly identical phrases, containing the exact same slang, and contractions, within seconds of each other?