Will driving slower really save you gas?

Lawton_Does driving slower really cut down on how much gasoline you use?  Many experts say it does, and one U.S. Senator is tossing around the idea of a 55-mile-per-hour national speed limit to cut down on the nation's gas consumption since the U.S. Department of Energy says fuel efficiency drops sharply when vehicles travel at speeds over 60-miles-per-hour.

But, how much gas will you really save?  Will you save any gas at all?

7News set to find out in an unscientific experiment.  7News took a trip from Lawton to Wichita Falls, driving 55-miles-per-hour on the way there.  On the return trip, the speed was bumped up to 75-miles-per-hour.  Before beginning the trip, 7News Reporter Monte Brown, and Chief Photojournalist Oliver Knop hit the road - they fueled up, making sure the tank was completely full, and not filling up with the 10% ethanol blend.  Then, they hit the slow lane.

"A 55-mile-per hour speed limit is just ridiculously slow," said 7News Mechanic Karl Boyer.  It felt ridiculously slow on the trip, seemingly barely moving on the turnpike south.  It took one hour and one minute to reach Wichita Falls, where once again, the tank was topped off.  The trip used 3.6 gallons for the 54-mile trip in a Ford Windstar.

On the return journey - finally moving at the turnpike speed limit of 75-miles-per-hour - the trip only took 50-minutes...11-minutes less than driving 55-miles-per-hour.  The travel time wasn't too surprising, but the pump reading was.  The trip only used 2.4 gallons on the trip back to Lawton.  "It's an oddity that the faster you run the better your gas mileage was, but to explain...we don't know," says Boyer.

Boyer says there are a number of factors that could have skewed the results - including tire pressure.  "The faster we run, the more air pressure we gain in the tires and less ground resistance we have.  Of course wind resistance coming across the car could have caused some of it."

Boyer says he believes modern fuel-injected cars are designed to drive faster than old carburetor engines, so he was not too surprised by the results.  But, he says there's a simple way to decide which speed to travel.  "If a man wants to drive 55 to save gas let him drive 55.  If the man can afford 75 let him run 75," he says.  "Run a comparison and see where you get your best gas mileage.  At my shop 85 might be the limit we need to run (laughing)."  Boyer says the biggest impact on your gas mileage is ethanol blended fuel - he says it will decrease your gas mileage by about 10 to four miles-per-gallon.

This was an unscientific experiment, but the findings were similar to another news station's investigation.  They, too, used less gas at 75-miles-per-hour on a trip between Tulsa and Oklahoma City.