Driving Green on Regular Gas

“Depending on your vehicle’s design, an active A/C can cut fuel economy by anywhere from 3% to 10% percent in standard summertime temperatures. During a brutal heat wave, though, the power drain can be near 20%–the hotter it is outside, the harder the A/C needs to work at maintaining your cabin climate,” he writes.

The reason you don’t want the windows open on the highway is that as the car accelerates, drag (which increases with the square of the speed) becomes more of a factor and the car has to work harder to battle wind resistance.

The rest of Koerner’s column illustrates how hard it is to get credible information on green driving. The test data he was able to find, from the Society of Automotive Engineers, dealt with only two vehicles, an SUV and a full-size sedan, both with eight-cylinder engines, so it’s a little hard to determine exactly how that translates to the dozens of other auto types that Americans drive. At least we have a rule of thumb.