With gas prices on the rise I started thinking about my driving habits, and how I can get a little further down the road on a little less gas.

I’m not a big speeder.  Five mph over the limit is about as fast as I’ll go.  But I started thinking about the value of going faster. I even broke the analysis down a single mile per hour.  How much time do I save for each mile per hour over the limit, and how much more does each mile per hour cost me?

The results are quite interesting…

I used 60 mph as a baseline, as I figured that’s a good ball park speed for the most economic speed for most vehicles.  Depending on your vehicle it could be a bit more or less, but it’s a start.

Let’s say you drive 65 miles per hour instead of 60.  Driving that extra 5 mph faster saves you 4.6 seconds per mile (i.e. it takes 138 seconds less to drive 30 miles at 65 miles per hour vs. 60 mph).  But, the catch is that your fuel economy drops by a significant amount, for each 5 mph over 60 you drive. 

According to http://www.fueleconomy.gov, for each 5 mph over 60 you drive, you add $0.21 per gallon to your fuel costs (based on $2.50/gal gas).  So, if your car gets 30 miles per gallon, saving that 138 seconds (2 minutes 18 seconds) cost you 21 cents. 

Do you drive that same 30 miles back and forth to work, five days a week?  You’ll save a whole 4 minutes and 36 seconds out of your busy day by driving faster, but it will cost you $0.42 per day. Over the entire year (~260 work days) it will cost you $109.20 to save less than 5 minutes per day.

If you drive 75 mph in a 70 mph zone, the costs are even higher, as the effficiency does not go down linearly.

It’s pretty interesting (daunting?) after you can quantify how much your time costs. 

Looking back over all the highway driving I did last year, and I would guess that the majority of the time, the time I saved was not worth the cost.

I think I’ll keep the speed down next time I’m on the road.

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