This is an annoying problem that I find particularly annoying. Usually when you ask a guy why the truck is idling, there is rarely a rational response. (With tour buses it can be to keep the air moving which I can understand on a warm day when passengers are soon to board.) I try to ask them why they do it (out of genuine curiosity) and I have gotten shrugs, and other non-answers. Once a guy's response was, "It can't hurt the engine." I don't know what that means, but that's what he said.

In Philadelphia there is an ordinance against it as well as a brochure from the Clean Air counsel (links below). A suggestion might be to give the driver the brochure. On a related complaint, every day in front of the Bellevue on Walnut Street there sits two buses - one from DLC Transportation - doing the same thing. I have called the "Air Management Unit" who said they'd send someone out - nothing has changed and the city apparently doesn't enforce the ordinance.

There's also a state statute which I just found - there are restrictions: 35 P.S. § 4603