Although back in the 70's there were cars that achieved between 50 and 100 mpg todays cars have the potential to get much better. The engines are getting smaller and more powerful... ever wonder why?
Toyota has a prototype that gets 104 mpg but by their own admission will never go into production. Look up the Toyota ES3 (Eco Sprint cubic). This is a hybrid/diesel combination. Or better yet how about a 265 mpg VW... although a bit awkward, is a tandem 2 seat with a 1 liter diesel. What do you suppose Ford, GM, and Daimler-Chrysler is up to? I believe they have more to do with trying to keep them out as opposed to trying to compete with them. Just think of the money being spent on marketing these big expensive low mileage vehicals.
Gee even the government promotes gas guzzelers by giving tax breaks for those that own them... are they really concerned about the environment? Probably more concerned with their pocket books. It's not technology thats to blame here its Politics. Actually the average mpg now is lower than it was in the 80's. The government wants to set standards for fuel economy of 35mpg by 2010... 35mpg? The US is only 5% of the world population and accounts for 25% of the worlds energy use ... AND contributes 36% of all greenhouse gasses!
The technology is already here.... multivalve engine for better flow, change valve timing during light loads and close the exhaust valve sooner(6% increase in efficiency), let the computer set up lean burn for light loads as in crusing down the highway( another 6% in efficiency)... Optimize the transmission with better gearing ( up to 9% increase in efficiency). The list continues including materials other than steel, better tires, low friction lubricants, aerodynamics, more efficient pumps, alternators that work from the motion of the car (free recovery of lost energy), more efficient power steering units and on and on and on....
You see the point any way... whew... I feel better... But I've only touched on a very small and tiny tip of what could be... and in all reality should be.
Have Fun
Ed