New clean diesel engines offer better fuel economy and lower emissions than their gas counterparts, so why aren't they more popular in the U.S.? That's the topic on this edition of Autoline EXTRA. John and his guests discuss why there are not more diesels in the U.S. and whether or not something should be done to promote them. Joining in the discussion is Dan Weiss from the Center for American Progress, Fred Smith of the Competitive Enterprise Institute and Ron Cogan from Green Car Journal.