I drove by a bad car accident this evening, which caused a pretty large traffic jam. It was clear when I got there that traffic was not moving, so I (and I alone) turned my engine off. There were probably about a thousand or so cars waiting to get by, not moving, and all I could see were still running, evidenced by a long line of brake lights in front of me and headlights behind me, all making the fog from cars' tailpipes glow like fire. I really wanted to yell out to everyone there that it's really not beneficial to anyone to keep idling like that, as if they couldn't see that traffic ahead was not moving and would not move anytime soon. (The highway was crossing a wide valley between a pair of low hills, so there was a very long line of sight.) Why do they keep their engine running? Traffic did move forward a few dozen yards every once in a while, but between those, I just kept the car parked.