Yeah, the idea of lowering speed limits has been brought up before, with the intent on lowering the emissions and fuel usage by forcing people to drive slower. This would work, of course. The slower an engine turns, generally the less fuel it is using. And, generally, the less fuel that an engine is using, the less emissions are being produced.
Maybe we should propose adopting a new slower speed limit, like is being done on one street in ChangSha, China. On this street the speed limit is 5 kilometers per hour, which is just over three miles per hour. So, anything over a gentle walk is speeding. No jogging! Some motorcycles and scooters would have to be banned, because they are too difficult to control at that speed. No problem, though, just get off and walk! The world's emissions problems solved!
[Source: Weird Asia News]