Dear Tom and Ray: I'm considering buying a hybrid car, but someone recently told me that because I do a lot of highway driving, I will not get nearly the mileage promised in the ads. The reason I was given is that on the highway, the gasoline portion of the engine is used rather than the electric portion. Is this true?

Gayle

Ray: Well, Gayle, no one ever gets the mileage promised in the ads. But it's true that the benefits of hybrids are tilted toward city driving.

Tom: Here's why: Hybrids combine a gasoline engine with a battery-powered electric motor. In Toyota's hybrid system (which is the most popular), the battery power is called on first. So if you're just driving gently in city traffic, you might use ONLY the battery a lot of the time. And if you're stopped at a light, you're using nothing!

Ray: That's when a hybrid will save you a lot of gasoline.

Tom: At higher speeds -- above 15 mph or 20 mph -- or on harder acceleration, the gasoline engine kicks in. And, while the battery is still assisting the gasoline engine, you rely much more on the gasoline engine. So, at highway speeds, you still get good mileage, but the boost isn't quite as great as it is around town.

Ray: Incidentally, the reason nobody gets the Environmental Protection Agency-rated mileage in their car is that the tests are totally unrealistic. The tests are done with all of the accessories off, including the heat and air conditioning. In reality, most people have at least some accessories on all the time. Every accessory requires some power and lowers your mileage.

Tom: What makes the difference even greater on a hybrid is that turning on a major accessory, like the heat or AC, automatically turns on the gasoline engine. So, even at low speed around town or when you're stopped at a light, if your AC is on, your engine is running and you're using gasoline.

Ray: The Prius EPA test claims ratings of 60 mpg in the city and 51 on the highway. We have yet to meet anybody who gets even close to that. Most Prius owners we talk to get somewhere between 40-50 mpg -- which is still fantastic! You might be very happy even at the lower end of that scale, Gayle. But the mileage is not what the EPA leads you to believe it will be.

Tom: So, it's time for the EPA tests to join the real world. Turn on the AC, let a few pounds of air out of a couple of tires, and throw a mother-in-law or two in the back, and then we'll see some real-world mileage estimates.