i work at the port and have talked to the department of transportation mvcd or wtv there called on numerous occasions about such questions. these people are state officers who regulate trucking and interstates and highways. one of my good friends is a sargent and he told me that as of right now the government has no plans to start messing with diesels, atleast older trucks that are pre emmisions. he also said that becouse 100% of semi's are diesels that "the government would be biting off more than they could chew" as he put it. he also told me that i cannot get a ticket for smoke and that if anything does change it will be up to the states to determine such laws.