Mileage: Wild Driving Can Cost $100 More in Gas Per Month Bernd Opitz / Getty Images How can one driver average 37 m.p.g. and get 575 miles per fill-up, while another driver - driving the same model car - tops out at 21 m.p.g. and 325 miles per tank? The answer is that these two drivers drive very differently. You've probably heard, and ignored, advice on how to get the best mileage in your car. The Internet is loaded with tips for upping your average m.p.g., including inflating tires properly, taking it easy on the gas and brake pedals, and emptying the trunk to lighten the car. We all know that vegetables are good for us too. That doesn't mean we'll do what's best for us. Perhaps behavior would change if a dollar figure were attached to the equation. To prove just how big of an impact driving habits and vehicle maintenance have on a car's mileage and fuel costs, General Motors recently conducted an experiment in which two of its fuel-economy engineers commuted to work in identical Chevy Cruze LTs. In this morality tale, one engineer (Beth Nunning) was the bad driver who sped on the highway and floored the gas and pounded on the brakes in traffic, while her counterpart (Ann Wenzlick) demonstrated more exemplary driving habits. Much like the fable of the tortoise and the hare, it's the steady and conscientious, if slow of foot, competitor who comes out the clear winner. Wenzlick, who used cruise control and maxed out at 70 m.p.h. on the highway, compared with Nunning's 80 m.p.h., averaged 37 m.p.g., according to GM. At Wenzlick's pace, a tank of gas in the Cruze would last 575 miles, and she could expect to pay $1,621 per year to fuel up. Nunning, on the other hand, drove like a jerk, hammering on the brake and gas pedals and going over the speed limit. The car's tires were underinflated by 5 lb. each, and the trunk was filled with 240 lb. of unnecessary stuff. She also wasted gas by doing things like keeping the windows open on the highway and idling at the drive-through for 15 minutes to order a coffee, instead of parking the car and going inside. Nunning's numbers came in at just 21 m.p.g., for 325 miles per tank. That would work out to a yearlong cost in gas of $2,857 - $1,236 more than Wenzlick's cost. While the difference in gas mileage and costs is eye opening, it's not nearly as impressive as the exploits of the so-called world's most fuel-efficient couple, John and Helen Taylor. The twosome, who hold dozens of fuel-efficiency records and seem to work full time in pursuit of maximum mileage, recently completed a 9,000-mile tour of all lower 48 states, averaging just under 70 m.p.g. in a hybrid car. After that, the Taylors employed their obsessive slow-driving strategies on a three-day trip from Houston to Virginia, averaging 84 m.p.g. in a Volkswagen Passat diesel. Normally, the Passat diesel gets 43 m.p.g. on the highway and can be driven up to 795 miles with a single tank. The Taylors drove their Passat a whopping 1,621 miles on one tank. That's pretty amazing. But I have to wonder about the idea of taking a road trip for no other reason than trying to get the best mileage. No matter how lofty one's m.p.g. average, isn't such a feat basically, you know, a waste of gasoline? Tuttle is a reporter at TIME.