1. Hybrid cars are not intended to save fuel, and do so poorly. They are intended to reduce emissions. The reason they exist is that auto makers are required to reduce their overall emissions and to provide some zero emissions vehicle by law. In order to continue producing luxury trucks with inefficient pushrod V-8 engines, they must produce a token amount of the hybrids, on which they lose money. When you purchase one you are personally producing less pollution as you drive, but the overall problem is not solved, nor are these vehicles a solution of any kind to the problem of the car.
2. Biodiesel requires more petroleum to produce than ordinary petroleum-based fuels, according to recent studies. This is because industrial agriculture in the United States requires so much energy, from the nitrogen fixation to the machinery used, that the fuel oil produced from crops is basically inefficiently converted oil. Biodiesel is a great idea if you already have a source of free biomass around, and it is a great idea for a small number of vehicles that can live off the waste biomass others discard. The overall problem is not solved, nor are these vehicles a solution of any kind to the problem of the car.
3. Ethanol and ethanol-gasoline mixes do not reduce the U.S. dependence on foreign oil. Ethanol is made almost entirely from corn. The corn is indeed domestically grown in huge quantities and not imported. However, the corn yields depend absolutely on high-powered artificial fertilizers which require so much energy to produce that they are basically congealed electricity. Unless the plants that produce these fertilizers are somehow powered by some unknown renewable or domestic energy source, this country is still absolutely dependent on oil to make the fertilizer so that the corn can be grown and converted into ethanol. When there is a surplus of corn and a temporary shortage of petroleum, ethanol is a fine idea, because it reduces the consumption of gasoline in the short term. The overall problem is not solved, nor are ethanol-based fuels a solution of any kind to the problem of the car.
4. Great strides have been made in improving the passenger car. If the current technology was appropriately used to its maximum, pollution and fuel consumption from cars could be reduced tremendously. However, almost everything in this country is distributed by truck. It would be difficult to change this, because the country is very spread out. Commercial trucks predominantly use older diesel engines which are inefficient and dirty. Even if every new truck sold was required to be much, much more efficient and clean, the current trucks would be on the road for a long time. Trucks are rarely replaced; they are repaired. It’s very expensive to replace them. Any large-scale change in the trucking industry would require a tremendous amount of government subsidy to compensate the small companies and individual contractors who own these trucks, because they can’t afford to upgrade. A sharp increase in the cost of trucking would be felt throughout the entire company. There is currently no good solution to the problem of the truck.

Have a nice auto-doom!