A new study from the University of Michigan Transportation Research Institute (UMTRI) has determined the precise effects of vehicle selection, maintenance and driving style on an individual driver's fuel economy. The results? No matter what you drive, your car can be a gas guzzler.

Not surprisingly, choosing a fuel-efficient vehicle has the biggest single impact on how many miles per gallon a driver can get. Whether you buy a gas guzzler or fuel miser accounts for 28 percent of your individual fuel economy, regardless of how you drive or how the vehicle is equipped. It gives credence to policies that encourage car buyers to choose efficient vehicles, as real-world mileage can only vary so much from the number on the window sticker.

Cumulatively, however, individual choices that a driver makes with an existing vehicle can make a Chevy Cruze's mileage match a Suburban.

Study authors Michael Sivak and Brandon Schoettle examined the effects of a driver's decisions on a hypothetical high-mileage car, one so neglected by its owner that it's out of tune with low tires, the throttle pushed to the limit after every stop sign and the trunk full of scrap metal. In such a state, that poor car's mileage could decrease by about half.

"Following the remaining best eco-driving practices will result in no change in fuel economy for the car that gets 11 mpg," Sivak and Schoettle wrote. "By contrast, the car that nominally gets 36 mpg will experience a reduction to 19.8 mpg in actual fuel economy."

Many of the authors' recommendations read like one of those "improve your fuel economy" pieces that local news stations run every time gas prices start to go up: Keep your engine tuned and your tires properly inflated. Don't speed, don't drive aggressively and clean heavy debris out of your trunk.

However, the authors also calculated exactly how route planning can affect mileage. Commutes that avoid hills and congestion can affect mileage by up to 40 percent. As navigation systems begin to better detect traffic patterns and road topography, the Michigan research could be used to instantly calculate the estimated fuel economy for different routes, letting the driver take into account the cost of a journey.

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Photo: Flickr/M.Markus