Our Odyssey, which weighs 4300 lbs, gets 24-25 MPG at 80 MPH. That is not great gas mileage, but it is when you consider that it is carrying five people and lots of luggage. If I drove at 60 it would get 28-30. Gas would have to be $10 a gallon for that to happen. An SUV or pickup of the same weight and carrying capacity would get 10 MPG at 80 MPH. Why? It's called wind drag. The reason the Odyssey (and the Prius) get such good highway mileage (each for their size) is streamlining. At interstate speeds (75 here in Idaho) the hybrid nature of the Prius is not relevant, but the shape, narrow tires, etc, are.

I know that in a few years gas will be $10 a gallon, due to market forces. By then there will be lots of highly streamlined cars to buy, not necessarily hybrid, which is not very advantageous where there is no traffic. I'll buy one. BTW, it will probably have lots of horsepower and go from 0-60 in 6 seconds. And that have no effect on the gas mileage, because if all it takes is 40 HP to travel at 80 MPH, that is all the gas it will consume, whether the peak HP is 300 or 90.

The two major causes of high gas consumption at cruising speed are wind drag and pumping losses. If an engine is perfectly sized so that it requires maximum HP to cruise at some speed, the throttle will be wide open and pumping losses will be minimized. However, no one would want such an underpowered car. There are two ways to reduce pumping losses, the first being used by some cars is to shut off some cylinders. This requires a wider throttle opening to produce the required HP, reducing pumping losses. The other way, which is superior, is to have additional ratios in the transmission to reduce RPM's to a low level. In order to maintain the required HP the throttle has to be open more. Many cars now have 6-speed or even 7-speed transmissions for this purpose. So, by having variable valve timing, which allows the engine have lots of torque over a wide RPM range, an engine can comfortably operate at a very low RPM, where the maximum HP is minimized, and the throttle is open quite far. So despite your high school physics expertise, you really can have lots of power and good gas mileage. We'll talk about engine friction losses some other time.

You might be right on the acceleration, but consider this: rapid acceleration implies wide open throttle with its reduced pumping losses. Over-acceleration which would require excess braking would consume more fuel, but rapidly accelerating to a steady speed might be more fuel efficient than slower acceleration. Ideally, the way to accelerate is to get in the highest possible gear so that large throttle openings are required for adequate acceleration. Most automatics shift down under those conditions, but I have noticed that my Odyssey is reluctant to downshift unless I give it lots of throttle. And I have never gotten less than 20 MPG, even in town driving.

My approach to getting good mileage is to treat the brake pedal as forbidden territory, and to drive so as touch it as little as possible. After all the frictional heating of the brakes is directly equivalent to wasted gasoline.

In the old days of muscle cars cars burnt lots of extra fuel. The extra fuel cooled the engine and allowed the engine to run at its most powerful fuel-air ratio. They got terrible mileage. Now with computer controlled engines, and also much better engine designs we can have efficiency and power at the same time. I read somewhere that a GM V-8 of the 1960's cost GM $25 to build. In todays dollars that would be maybe $200. I suspect that our much more complex engines of today cost more.

Variable valve timing, which flattens the torque curve, allows efficient operation at low RPM, which reduces engine friction and pumping losses. Yet these same engines when revved to 6000 or more RPM produce gobs of power. So a modern engine with a six speed transmission can drive a car at 80 MPH at less than 2000 RPM, and by shifting down and revving up can deliver 250-300 HP with no efficiency penalty. Small cars of the '80's weighed around 2000 lbs; they now weigh over 3000, except for the very small cars now on the market. The engines of the'80's would get terrible mileage pushing todays (relative) behemoths.

Those who are old enough can remember the Messerschmitts and BMW Isettas of the '50's. If they were out today with modern engine technology they would probably get 80 MPG in the city. And if you got hit by a modern sub-compact you would die.

The Insurance Institute of Highway Safety has a web site that charts the death rate per million registered vehicles of almost all cars on the road. My Odyssey has one third of the fatality rate of a Suburban, for example, so size isn't everything. But a car can get so small that it is inherently hazardous to drive it. So we will have fairly heavy cars for the foreseeable future , but modern engine-transmission combinations and hybrid technology will sure help. I think we will have $10 gas within five years. Make your plans accordingly.