柴油机车被越来越多的人认为是主要的污染源.

But locomotives are increasingly recognized as a significant source of pollution.

研究小组将高速列车同汽车，火车（美国的全国铁路乘客公司的柴油机车）以及飞机的排放周期进行了比较。

The team compared the lifecycle emissions of high-speed electric rail with transport by car, by heavy rail (the Amtrak diesel system) and by air.

最近，牵牛星（Altair）产品设计向公众透露了他们所说的世界上首批液压混合动力公共汽车，并说，这种混合动力车能够节省出一辆传统柴油机车能节省的燃料的两倍。

Altair Product Design recently unveiled what it says is the world's first series hydraulic hybrid transit bus and says it delivers twice the fuel economy of a conventional diesel bus.