I can't drive 55, but I'll think about 60

When you drive from Atlanta to Greensboro and back you have to play a little game. The game starts about a week before you leave from Atlanta, when you start trying to make sure that you have exactly enough gas left in your gas tank when you leave to just coast across the South Carolina state line on fumes. If you do it right, you can fill up your whole tank at about 20 cents per gallon cheaper than in Georgia thanks to the lower taxes. Then you drive to one of the last gas stations in SC, fill up again, and see if you can do whatever you need to do in North Carolina and make it back across the line again without having to fill up.

Usually I'm driving around in Greensboro for a couple of days, so it's not easy to not have to fill up, but this last time I happened to just make it. The empty light clicked on just past Charlotte which is still 30 miles or so from the cheap gas, so I slowed down a bit to make sure I didn't run out.

Doing that reminded me to try an experiment I'd been meaning to do for a while but kept forgetting. I've always known in theory that you get better gas mileage driving at 55 or 60 than you do at 70 or 75 mph, but I've never known how much, and whenever I've tried to figure it out I get frustrated driving slowly and start driving normally again. But since it's exactly 100 miles between the first and last gas stations in the state on I-85, I figured I could grit my teeth and set the cruise control and drive 60 just that far to see how much difference it made.

I was in our 1998 Mazda Protege with 140k or so miles, and that little junker already gets good mileage, usually about 30mpg on the highway. I had reset the trip odometer at the last fillup, so I was able to tell that for that tank of gas the ol' Mazda got 31.09 miles per gallon. That was including probably 15 miles of rush-hour traffic in Charlotte and probably 40 miles of in-town driving in Winston-Salem and the rest freeway speeds of 70-75, so pretty good.

I was expecting my 100 miles of slow driving to increase that somewhat, but since the mileage was already pretty good I didn't think it would make that much difference, maybe get me up to 35 mpg or so. I doubted that would be enough to make it seem worthwhile to me to change my driving habits significantly, but it'd be worth 100 minutes to see.

When I filled up again 100 miles later before crossing back into GA, I'd used 2.25 gallons of gas - which meant my gas mileage had gone up to 44.44 mpg! Granted, that's under pretty much ideal conditions since I hadn't hit any traffic and so had never slowed down or stopped, but still!

So at $4/gallon average driving 60 mph across South Carolina cost me $9. At 70 mph, it cost me $12.87. At 60 mph it took me an hour and 40 minutes and at 70 mph an hour and 25 minutes or 15 minutes faster. So the financial savings of slowing down would be $15.48 per hour.

Whether or not that's worth it depends on how much I want to be wherever I'm going a little faster, of course, but I was surprised at how much difference the 10 miles per hour does make. Those of you in California and elsewhere where it's even more expensive per gallon could save more if you can get over the indignity of being passed all the time by 18-wheelers and little old ladies.

Fortunately, probably because gas prices are so high I think there are more people driving that speed than in the past. So even if you're driving 60 mph, you can still look down on those wimps who are only going 55.