海角大神

Saving Pennies or Dollars is a new semi-regular series on The Simple Dollar, inspired by a聽聽concerning frugal tactics that might not really save that much money. I鈥檓 going to take some of the scenarios described by the readers there and try to break down the numbers to see if the savings is really worth the time invested.

Gayathri writes in:聽Driving 1mph slower than posted speed limit. Yeah, that鈥檚 a myth.

Actually, it鈥檚 not a myth. Most cars made in the United States maximize their fuel efficiency at about 55 miles per hour and drop off聽rapidly聽above that limit (this is actually from a study 鈥� West, B.H., R.N. McGill, J.W. Hodgson, S.S. Sluder, and D.E. Smith,聽Development and Verification of Light-Duty Modal Emissions and Fuel Consumption 海角大神 for Traffic Models, Oak Ridge National Laboratory, Oak Ridge, Tennessee, March 1999).

This means that if you鈥檙e tooling along on the interstate at the speed limit of 65 miles per hour and drop that back to 64 miles per hour, you鈥檙e actually improving your gas mileage by about 1.5%, according to聽.

So, let鈥檚 work out what that鈥檚 really worth.

Let鈥檚 say you have a typical car that gets 25 miles per gallon at 55 miles per hour. At 65 miles per hour, it鈥檚 going to get roughly 15% worse gas mileage, or 21.25 miles per gallon. If you trim that back to 64 miles per hour, your gas mileage is a bit better 鈥� you鈥檒l be getting 21.625 miles per gallon, more or less.

Now, let鈥檚 say you鈥檙e going on a 400 mile trip on the interstate and that gas is available for $3.25 a gallon.

If you go 65 miles per hour, it will take you 6 hours and 9 minutes to make the trip. You鈥檒l burn through 18.82 gallons of gas, which will cost you $61.17.

If you go 64 miles per hour, it will take you 6 hours and 15 minutes to make the trip, six minutes longer. You鈥檒l burn through 18.5 gallons of gas, which will cost you $60.13.

In short, driving one mile per hour slower will add six minutes to the trip and save you $1.04 in gas.聽Your savings simply by driving one mile per hour slower is $10.40 per hour.聽That, of course, is after-tax money.

That figure, as mentioned above, assumes a 25 mile per gallon car, but other mileages have similar savings. It also assumes that you鈥檙e slowing down a bit from a speed above 55 miles per hour.

厂辞,听should you just go 55 on any road you鈥檙e on?聽I wouldn鈥檛 do that. Instead, I鈥檇 stick to the posted speed limit and maybe go a mile an hour or two below that in the slower lane on an interstate.

Doing this serves three purposes. One, you鈥檒l put cash in your pocket for the extra time you spent driving. Two, you鈥檒l never get a speeding ticket. Three, you鈥檙e sticking more or less with the flow of traffic (going much slower would disrupt that), so you鈥檙e not disrupting traffic flow and endangering yourself that way.

The next time I鈥檓 rolling along some flat four lane road in southern Iowa, I鈥檒l just set the cruise to a couple of miles per hour below the speed limit and roll along. Sure, I might get there five minutes later, but I know I won鈥檛 get pulled over for speeding, I鈥檝e got something entertaining on the radio, and that bit of extra time will put a bit of money straight into my pocket.