A group of us took our kit cars to Sweden for a trip. We didn't know about the pollution rules and got asked to turn off our engines while we were sat in our cars idling while we waited for someone to join us.
It made us much more aware of the need for cleaner air and it was proof that it worked because all our cars got better mpg while we were in Sweden.
In the UK, although there are now cars that auto-switch off at lights or whilst stationary, there are still many, many drivers who seem unaware of the health and environmental hazards that are caused by exhaust fumes. Buses, coaches and taxis are the worst offenders plus over-protective parents waiting for their molly-coddled young to come out of college opposite where I live.