Slightly more than half of all vehicle makes on American roads are eligible, Dr. Campbell said.

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The new rules meant that Navistar, as well as rivals like Volvo, Mack, Freightliner, Paccar and Cummins, would have to redesign all their engines for American roads, using technologies that were less than perfect or inventing new ones.

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After all, almost 370, 000 people died on American roads between 2001 and 2009 and millions more were injured.

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