It helps, but you don't have to drive an econo-box appliance to save big on gas. Your decisions can put a big dent in fuel use -- up to a 45% savings, say two University of Michigan researchers.

Michael Sivak and Brandon Schoettle -- being colleagues at the green-friendly U-M Transportation Research Institute -- are quick to say that buying a fuel miser is the surest way to use less gas. Choosing a car (23.7 average mpg for 2011 models) over a minivan (19.4 mpg), SUV (19.2 mpg) or pickup (17.2 mpg) may be the easiest way to save gas.

"Nevertheless," says Sivak, "remaining factors that a driver has control over can contribute, in total, to about a 45% reduction."

They list some of the decisions anyone can make to save gas -- including some we hadn't thought about.

They split the eco-practices into strategic decisions (maintenance, beyond choice of vehicle selection), tactical decisions (picking your routes and vehicle load) and operational decisions (how you drive):

Strategic:

Keep the engine tuned, use the right oil and keep tires inflated (properly -- not waiting till the pressure monitor indicates a safety hazard). Obvious stuff, so its amazing how many people don't do it. But the researchers calculate keeping up on maintenance can boost mileage up to 40%. It's the easiest way to save, and a better-performing ride can be both safer and more fun, too.

Tactical:

Choose the flattest route for your commute or trip -- a flat route can yield 15% to 20% better mileage than a hilly route, they calculate, so might use less gas even if it's a little longer.

Ditto for picking a free-flowing highway route as opposed to a congested route, which can boost mileage 20% to 40%.

And jettison any extra stuff you're carting around -- an extra 100 pounds can cut your fuel economy up to 2%, they say.

Operational:

Less aggressive and slower driving can save up to 30%, so pick your times to let it out. Don't be perpetually impatient, particularly when it's not really saving any time and is really costing you gas.

Use cruise control on the highway (7% better than your right foot).

If you can take the heat -- and don't put down the windows at 70 mph, increasing drag -- turn off the AC. The researchers say that can save up to 25% -- though it would be much less if you have electric, not engine-driven AC.

Don't let your vehicle idle for more than a minute.

As always, the disclaimer: Your results may vary. The researchers note that the savings above are calculated based on "specific and sustained conditions." Unless you're in Kansas, a completely flat route, for example, is not in the cards.

Sivak and Schoettle say your actual total savings will be less than the sum of the maximum savings. But they calculate an overall potential swing of about 45% is under your control.

While vehicle choice is the most important fuel economy decision, Sivak says, "Following the remaining good eco-driving practices can still lead to a major reduction in on-road fuel economy."