Ford makes a Fiesta diesel in Germany that gets 63 mpg highway. I have read that the car companies are going to make more diesels for their bigger vehicles so they can meet the fuel requirements. American diesel has been cleaned up and sulfer removed. That extra refining makes it cost more. However, it is easier to make diesel than gasoline. Germany has 85% diesel vehicles on their roads. They cut their fuel imports drastically when they went to diesels. They average 30% better mileage for a comparable gasoline vehicle. They cost more than gasoline, but less than hybrids. In the next few years there will be more on the road.
We converted an F-250 diesel in Birmingham to a combination diesel-natural gas, and it gets 36 mpg diesel. I don't remembe how much natural gas equivelant was injected with the diesel. Both fuels run at the same time. Natural gas is about $1.35-$1.85 equivelant cost per gallon vs gasoline. Just need more compressor stations installed around the country.
The vehicle "fleet average" is the mpg government requirement. So they will still make big vehicles, but they will probably be diesel within 10-20 years. Small vehicles will probably be hybrids and diesels. If they made a diesel hybrid big vehicle or truck, one would probably get 30-50 mpg in them.
Chrysler makes an all plastic vehicle, except engine, drive train, wheels and axles, in Brazil. This vehicle is a 5 seater hatchback, no air, no heater, and gets 75 mpg. It has a two cylinder garden tractor air cooled engine. Sells new for about $4,000. It will not be sold in America because it doesn't meet our safety standards.