Well, if you've driven behind a Semi on the highway that has not been serviced in some time, then you'll know the Black noxious smoke that bellows out of the exhaust pipes. The problem is not so much that the trucks haven't been properly maintained, it's that they burn a Fossil Fuel similar to what is used in a common heating home furnace. # 2 Diesel fuel to be precise. The Diesel engine was NOT ORIGINALLY DESIGNED to burn "Diesel" fuel. The original design required the use of "plant based" oils like Corn or Palm oil. Ethanol, to be more to the current term. However, to produce Ethanol at the time when Diesels were first produced, was more expensive than distilling the "fossil fuel." Also, Diesel was more abundant. So "Diesel" became the fuel of choice. However, it does not take a major "modification" of the engine design to convert a Diesel engine to run on Plant oils. Some people have already done the modifications themselves. Using "used" cooking oil to power the engine. They "clean up" the used oil and actually run the engine on it. With the current Farm Output and Farmers finding themselves "suffering" economic loses on some crops on the Global Market, perhaps the concept of using Plant Oils for fuel (which actually burns cleaner) vs Fossil Fuels to power Diesel engines is the answer. The cost for Diesel Fuel is higher than the cost of Gasoline, now would be the time as producing Ethanol would be equal to or less than the cost of Diesel Fuel per gallon. The Liberal Democrats who are touting "Global Warming" as a major issue would go for this. The Republicans, in going along with this, would score a major political point. It's a Win / Win situation for all involved. Except of course, BIG OIL.