I owned a manual trans Ford Festiva for a couple of years. I got a consistent 45 MPG without even trying. I was suprised at how perky the acceleration was, but if you had a second person in the car you could really feel the drag. The top speed was about 75 on level ground with one person, so gearing was low to help the tiny engine. After digging some, I found it was a re-badged Kia from South Korea, and I was impressed with its reliability.
In 2008 or 09 diesel cars will be more available in the US. Most manufacturers were not interested in having a diesel option when their are 5 important states (California is a big market by itself) where the old style diesel didn't meet the newer European clean diesel standard because USA diesel fuel had high levels of sulfur.
You could buy a diesel VW or Mercedes in Arizona, but you had to put 7,000 miles on it before you could "move" to California and register it there. (Cordless drill on the odometer cable?).
Sulfur acts as a lubricant, and when removing it (in 2006-7) refiners had to add something to replace it, and the government ramped up bio-diesel production with incentives, so bio-diesel is added at about 5% as a fuel pump lube. All USA diesel fuel in 2008 meets the new clean diesel standard.
Current diesel engines have more excursions into a rich and lean condition when RPM's cycle than gasoline engines. When rich, the new exhaust has a soot trap. When lean, some low-oxygen exhaust gasses are bled into the intake (Exhaust Gas Recirculation-EGR). To reduce cylinder heat (and thus NOX production), the new diesel EGR (unlike gasoline EGR) is cooled.
Rather than have an old-style mechanical fuel distributor (at 18,000 PSI), the new clean diesels have electronically controlled fuel injection. Because of how thick diesel is, the newer diesels use 30,000 PSI for finer atomization, and a cleaner burn.
All new cars need to meet the new front-and-side impact standards (heavier, more expensive), and the tiny cars that are available in the USA have a more powerful engine and a higher final drive gear ratio than the old Festiva. This improves the two-person top speed, but lowers the one-person mileage. The VW diesel Lupo gets ~80 MPG, but doesn't meet the new USA crash standards. It probably also would NOT be enjoyable to try and cross mountainous Colorado in a Lupo with three people in it, but it is selling in Europe ($5-$6/gal).
Companies will only survive if they produce what the consumers are buying, so we must blame all of us for some of this.
My wife is resistant to us getting one of the 80's VW/Mercedes diesels (but she doesn't mind me building an electric bike). My community won't allow me to have a windmill or a clothes drying line. (A single tear slowly rolls down Rons cheek as the camera close-up captures the sadness and frustration in his eyes...)
"We don't like their sound, and guitar music is on the way out." - Decca Records memo, rejecting the Beatles, 1962.
<BR