General Motors fuel economy engineers Ann Wenzlick and Beth Nunning recently ran an experiment. Both drove a 2012 Chevrolet Cruze for a typical workday to figure out the best and worst ways to improve fuel economy for any vehicle.

The 2012 Chevy Cruze gets an EPA estimated 25 mpg (city), 36 mpg (highway) and 29 mpg combined when equipped with a 1.8 liter, 4 cylinder engine, 6-speed manual transmission.

Driving the same vehicle but in very different ways, believe it or not, one was able to get 250 more miles out of a tank of gas.

Wenzlick used the following tips to maximize her fuel efficiency:
1. Get out of the drive-through lane. Idling for just 15 minutes can waste a quart of gasoline.
2. "Take it easy! In the city I accelerated smoothly while Beth demonstrated one of the most common mistakes we see on the road: Jumping on the gas at every light, only to hit the brakes as she caught up with traffic. Such aggressive driving isn't going to get you home any faster; but driving smoothly can improve your mileage by 20 percent."
3. Driving at 70 mph, not 80 mph.
4. Use cruise control.
5. Roll up the windows. At slow speeds, turning off the AC can save you a little but I always roll up the windows on the highway. Beth was driving with her windows down and the increased air pressure acted like a parachute trying to slow her down, consuming much more energy than her AC ever will."

Nunning drove her car demonstrating common mistakes:
1. Low tire pressure.
2. Using roof ornaments. "To show support for my Detroit Tigers, I put up window flags on my Cruze for every home game. Unfortunately, at highway speeds up to a third is used to overcome wind resistance so even small changes to your vehicle's aerodynamics will have a big impact on fuel economy."
3. Carrying extra junk in the trunk.
4. Ignoring the 'check engine' light.
5. Not bundling errands. "An engine at operating temperature is up to 50 percent more efficient than a cold engine. So, when possible, it's much better to run five errands in an afternoon than running one errand every day of the week," she said.

How much of a difference does it make? Ann and Beth's results support data from OnStar that shows the fuel economy of drivers in identical cars can vary by 75 percent. With a well-maintained car, the best drivers get up to 25 percent more miles per gallon than average.

In this experiment, Nunning's inefficiency represents a cost of $2,857 annually; yielding 325 miles/tank. Wenzlick's efficient driving yielded 575 miles/tank. Wenzlick's efficient driving reduces the fuel cost to $1,621 annually. Subtract Nunning's totals from Wenzlick's and the difference between inefficient and efficient driving --in the same vehicle-- can reach 250 miles/tank and $1,236/year (given 15,000 miles a year at $4 per gallon).