What are the smoke signals?

摘要

In 1995, A United States-Based environmental pressure group's advertisement on New York City buses read: 'Standing behind this bus could be more dangerous than standing in front of if The source of danger at the rear was sooty particulates coming out of bus tailpipes. Fast-forward 15 years. Nowadays diesel engine manufacturers describe tailpipe emissions from the latest buses and trucks in the US as 'near zero'.rnThis remarkable turnaround has been driven by succeeding tiers of US Environmental Protection Agency emissions legislation, the most recent of which (EPA2010, in commercial vehicle industry shorthand) took effect in January.