It's a clever idea that is gradually spreading this Halloween season. You're trapped inside your car while horrifying monsters lay just beyond the glass. They invite you to come out to play.
To make it only scarier, I'd suggest having the car wash "break down" in the middle, trapping the passengers inside. Then, in total darkness, the clowns try to open the car doors.
This particular haunted car wash is in Cleveland which, of course, makes it only scarier.
-via Super Punch