I was at a party this weekend when the cops showed up presumably because of a noise complaint and demanded that everyone (except the residents) leave the apartment. I"m pretty sure the cops knew (or had strong suspicions) that kids had been drinking. I want to know why they would then request that people who have been drinking now get in their cars and drive. It seems a much sounder policy would be to make sure that everyone who left was able to drive under the legal limit.
I've thought that maybe it's a ploy to encourage drunk driving in the parking lot where a confederate cop is waiting to issue DUIs. I think that might be entrapment or something, but it could happen.