Recently, three engineers at the U.S. Department of Energy’s Oak Ridge National Laboratory have calculated the answer to this question. For example, if you drive 60 mph on your next trip, but you would like to instead drive 70 mph, be prepared to pay 16.3 percent more for gas, Oak Ridge says. At today’s average price, that’s like spending an extra 55 cents a gallon!
Oak Ridge National Laboratory is where the engineers decide on the fuel economy ratings for new cars. In this exercise, they tested 74 new and old cars and trucks at 50, 60, 70 and 80 mph. For every 10 mph increase, they charted the corresponding decline in mpg.
The results varied from one car to another. The fuel economy decrease was greatest when cars accelerated from 70 to 80 mph (15.4 percent) than when they went from 50 to 60 mph (12.4 percent).
Speed has its benefits when you have a deadline. If you set the cruise control at 70 mph instead of 60 mph, you’ll cut your travel time by 14.3 percent. On a 100-mile trip, you’ll arrive 14.3 minutes sooner.
But, if your car gets 25 mpg when you drive 60 mph, that comes out to 4 gallons for 100 miles. The Oak Ridge engineers determined that at 70 mph your fuel economy will fall by 14 percent, to 21.5 mpg. Now you’re up to 4.65 gallons, which means that you’re burning 16.3 percent more gallons per mile.
Recent average price for regular gas was $3.38 a gallon. If your fuel cost rises for that fast trip by 16.3 percent, it’s like paying $3.93 a gallon. (Want to drive 80 mph instead? Make that $4.65 a gallon.)
Suddenly, speed carries a price and getting there 14.3 minutes faster costs an extra $2.20.