Fuel Economy Depends on Driving Style

This smart fortwo gets better highway fuel economy than most hybrids currently on the market.

Courtesy of Kristen Hall-Geisler

Speaking of driving style, a person's daily commute should also be a major contributing factor when buying a hybrid. As you can see from the fuel economy numbers on the previous page, some hybrids get better mileage around town than they do on the highway. That's because at lower speeds, usually up to about 40 miles per hour (64.4 kilometers per hour), full hybrid cars can run using only their electric motor -- no gasoline is used at all.

And, while stopped at red lights or in horrendous city traffic, the engine can cut off completely, and then start up again when the vehicle needs the extra boost. This is often referred to as idle-stop technology or start-stop technology.

If in-town, low-speed, start-stop driving is a major part of your day, a hybrid will probably get the better side of the gas mileage equation. But for long highway commutes at steady high speeds (the kind of trip where you may even be able to use the cruise control) gasoline- and diesel-powered cars might perform comparable to, or in some cases even better than, the hybrids.

For instance, a gasoline-powered smart fortwo gets 41 miles per gallon (17.4 kilometers per liter) on the highway, which is better highway fuel economy than all but the top two hybrid cars on the previous list.

So what's a hybrid car's overall impact on the environment? The answer may surprise you.