[jameshart]

That goes against my subjective experience. The contribution of buses and trucks in US cities is also significant, and my sense is that EU regs on those vehicles are more stringent than US. I particularly tend to notice how much -noisier- large US vehicles are than European equivalents in a city traffic environment, which tends to correlate with lower efficiency.

[maxerickson]

Europe generally has more stringent regulation and worse pollution than the US. It's many more people in a smaller space.

Noise isn't a good predictor though, a muffler is a drain on efficiency.

[happyscrappy]

Actually the VWs that were emitting 40x pollution in the US were only 10x of the Euro regs.

[zardo]

Eu has stricter PM limits, the US has stricter NOx limits.

[happyscrappy]

http://www.hybridcars.com/will-america-avoid-europes-clean-d...