Image: A truck engine is tested for pollution exiting its exhaust pipe as California Air Resources field representatives (unseen) work a checkpoint set up to inspect heavy-duty trucks traveling near the Mexican-U.S. border in Otay Mesa, California September 10, 2013. REUTERS/Mike Blake By David Shepardson WASHINGTON (Reuters) – U.S. regulators on … Continue reading U.S. regulators unveil final rule on truck emissions limits