here in Oz they create more than emissions - they have been the direct cause of many accidents & near accidents outside schools. As has been said they also cause/add to many road accidents.

I was recently listening to talkback after another accident at a school. After the accident the Headmistress had asked parents to park away from the school & walk back to collect their primary aged children, but even then idiot parents didn't listen to her & parked & double parked around ths gates & endangered their own & other children. Other parents rang up to report similar behaviour at other schools. We also have restricted speeds in school zones, ignored by the majority of drivers.

I live on the edge of the CBD in an area with lots of 4WD's & lots of rich folks. The vast majoriy in my area would never go off inner city roads, which were not even built for motor vehicles! I'm glad I don't drive.