Did you read the case in Crim where the guy fell asleep in his truck in his own driveway, with a bunch of empty beer cans on the passenger side?
Claimed he was mad at his wife or something and went out there to drink, then passed out.
He got off because they couldn't prove whether he was coming or going. No way to infer the driveway was the end of his trip rather than the beginning.
People get off all the time. What's the citation for that case? Whether the drunk was at the end or the beginning of his "trip," it would seem that the drunk still made or was about to make a "trip."