Everyone in Japan leaves their car running when they're parked. Every time we walk to the park to go running we walk past parked cars that are sitting idling while their owners are: reading, writing, emailing, talking on the phone, watching movies, smoking, sleeping - you name it, we've seen it. One time when we went running there was a guy who parked his car in front of our apartment and left it running while his wife sat inside it. He was moving boxes in and out of his apartment. When we came back from a 10.4km run (20 minute walk there, 50 minute run, 20 minute walk back) he was still moving boxes into the car and it was still running.
When we walked to a neighbourhood restaurant this evening we walked past a guy who was sitting in his running car watching a DVD and using an electric razor that was plugged into the car's cigarette lighter. When taxi drivers park on the side of the main road here to chat with each other they leave their taxis running.
Where am I going with this? I fantasize about turning these vehicles off for their operators and then giggling my ass off when they get upset. In Canada I would (and have) approach(ed) people who do this but here I lack the language skills to properly lay into people when they tell me to mind my own business. You polluting my air is my business and one day when I'm better able to I'll tell you. Or at least find out why idling vehicles are so prevalent here.
As a society we've become dependent on cars and we've decided that it's necessary to use them instead of mass public transit to navigate our cities. This causes a ton of unnecessary pollution - an amount that is increased by idling vehicles. If your vehicle isn't moving it shouldn't be running.
I remember my grandfather telling me that when he went to Switzerland he was amazed to see signs posted indicating that drivers were to turn off their vehicles at stop lights and were only permitted to turn them back on when the light turned green. I was amazed not at the law but that it hasn't been implemented world-wide. It's so simple to do but the effect would be amazing.
I discussed this last night with some friends and their objections were the objections that a lot of people have: it takes more fuel to start a vehicle than it does to leave one running; and, starters will need to be replaced due to more use of the ignition. I told them the same thing I tell everyone else I talk to about idling: those objections are simply not true.