"At a per-passenger-mile basis, rail is about three times as efficient as travel by car, in terms of fuel efficiency, and six times as efficient as travel by air, so there are pretty substantial pollution reduction benefits both in terms of greenhouse gases and other pollutants."

VOA: standard.2010.02.15

Clearly, if I did nothing more, but I took every car, doubled its fuel economy, its emissions would go to 50% of what they are now, no other changes being made.

显然，如果我什么也不做，但是我把没量车的汽油价加倍，汽车废气排放量就会是现在的一半了，别的不会有什么改变。

麻省理工公开课 - 固态化学导论课程节选

Clearly, if I did nothing more, but I took every car, doubled its fuel economy, its emissions would go to 50% of what they are now, no other changes being made.

显然，如果我什么也不做，但是我把没量车的汽油价加倍，汽车废气排放量就会是现在的一半了，别的不会有什么改变。

麻省理工公开课 - 固态化学导论课程节选