There are a lot of good points in this thread. Diesel and bio diesel are pretty much interchangeable these days. There are some crazy efficient diesel cars and although the cost and emission difference is not that much different than gas, when you can get the crazy mpg out of the diesel it just makes sense. I think I have seen it before on some sort of science show where they were running an electric car off of an on board generator and getting very high ratings for mpg. The thought that small cars are not as safe as big cars is simply not true. Also if you have ever seen large SUVs and big luxury sedans that have been caught in a tangle with a transport truck, no one survives those either. The big difference being that it is easier to write off a small car, in fact you can write them off in accidents that are not much more than a fender bender. A couple of years ago we were out shopping for a new car for my wife for her commuter car. Honda Civic gets better gas mileage than a a Toyota Prius and costs around half as much. Also the Civic has a more comfortable interior. Neither of those cars fall into what I would consider ultra efficient.