Encourage increasing U.S. Diesel refining capacity to lower prices

With today's cleaner burning diesel engine technology, why are us 'green-minded', newer diesel car owners being 'punished' at the pump? Diesel used to be cheaper than gasoline, and still should be; it doesn't take nearly as much energy to convert oil into diesel as it does gas. Also, diesel engines are 20% to 30% more fuel-efficient than gasoline. Carbon dioxide emissions are considerably less than gasoline on account of the increased fuel economy. More diesels are making their way from Europe into the showrooms of U.S. dealerships and with this growing demand, refining capacity should be increased to match.