There are two fundamental problems with this line of thinking in relation to vehicles:

• The Manufacturers are unwilling to participate except to the level of vehicle efficiency mandated by the government. The government is not going to change the efficiency improvement levels that are already in place. And the efficiency improvements do not sufficiently address things like trucks, SUVs, and the like.
• The Consumer is not going to go for such vehicles any time soon. The average consumer is only partly interested in fuel efficiency - size and amenities in a vehicle are also very much in the consumer's mind when a purchase is being considered. Then there are the aftermarket products, such as high-rise modifications to make a truck look as though it stomp a Saturn without going into four wheel drive, or a 500-watt stereo system (which often requires an oversized alternator to power, which, in turn, requires more fuel to power). If you look at the sales ratio of truck/SUV vs. passenger vehicles, and do the math of the comparable fuel ratings based on that ratio, you'll see what I mean. People don't want nice, efficient transportation, they want the ability to intimidate the 'nice' vehicles with something nearly the size of a half-track. They also don't care that those of us who strictly walk, bicycle, or use public transportation have an equal right to the road. I do all three (and don't own a vehicle), and it can get ugly at times. How many people do you know that hop into their hummer to go to the store for a gallon of milk? Bleah.