Slow down to save gas?

TigerHawk discusses current gas prices, and how they're not causing people to change behavior. Driving the New Jersey Turnpike at 66 mph, he was basically the slowest car on the road. This was observed, despite the estimated savings in gas usage caused by going slower. From an article he cites:

How much you stand to save depends on a lot of factors. With gas at $4 a gallon, a driver with a long commute - 400 miles a week - and a gas-guzzling vehicle getting only 20 mpg would save $18.74 a week by slowing down dramatically from 75 to 55 mph, extrapolating from the government's most recent figures on the subject. Even a more moderate deceleration - from 70 to 60 mph - would save that driver $11.74 a week.

Sure, I could save money if I drove slower, although the variability I observe in my gas mileage on similar long freeway drives (sub-30 to 35) makes me wonder if any savings would fall within the margin of error from other causes affecting gas mileage. Perhaps the number of times I have to brake because of a semi traveling under the speed limit in the left lane is the main cause of this difference.

But let me apply these numbers to me taking one trip of 400 miles. At 30 mpg, let's say the savings becomes $12.50. But there's an additional cost: time. The travel time while going 55 is roughly 7.3 hours, compared to 5.3 hours at 75. In other words, traveling slower would make sense if I value my time at less than $6.25 an hour. I don't, and I doubt you do, either.

And it could be even worse: what if the difference between traveling 75 and 55 is an arrival home at 11:30 PM versus 1:30 AM? In trying to save money on gas, you may incur a much greater cost, with a serious accident or death due to driving while tired and impaired. I'm reminded of an old series of Dilbert comic strips, where a coworker decides to save money by cutting his own hair, an act that leads to his divorce and being taken off the management fast track. It's another example of the adage penny wise, pound foolish.

Or should we say pound fuelish?