At least in Massachusetts, if you are drunk, asleep in your car, but it's not on a public way, you can't be arrested. I was a witness to a drunk driving hit and run where the guy was found asleep in his car in a park and the arrest was thrown out. It was at night, and while I could identify the plate, I couldn't see the driver's face. The owner claimed he wasn't driving that night and didn't know who was.
Incidentally, while awaiting for the trial, two other guys' case was thrown out. In that case the driver was off with one officer, and while he was waiting, with another officer in the cruiser behind, the passenger decided to roll and smoke a joint. The second officer came up, saw a coffee can full of weed on the front seat and told him to open the trunk where they found about 100kg more. No search warrant, no case.