I thought this was a pretty good reason to drive 65 mph instead of 75 or even 70, going from home (L.A.) to school (SLO) and back (about 400 miles roundtrip).
“Peak Performance: A U.S. Department of Transportation study averaged the fuel-efficiency curve for eight cars and light trucks.”
It’s one thing for my brother to tell me the highway mileage stat on cars is obtained while driving 47.5 mph and somewhere above that speed the mileage starts to go down. It’s another to see that at 70 mph I get the same mileage as at 15? And the sharp decline as the speed rises…
The rest of the page:
Teutonic Shift: Freedom to speed is an inalienable right in Germany—at least on those portions of the nearly 8,000 miles of autobahn that have no posted limit. Some drivers well exceed 450 mph. So there was an uproar when a European Union official suggested last year that Germany cut greenhouse emissions by imposing a limit of 75 mph or so on the entire expressway.
The idea has merit. Cars burn fuel to overcome friction, air resistance, and other forces allied against them. The more fuel a car burns, the more CO2 it produces. Every car has a peak fuel-efficient speed that gains the greatest distance per unit of energy spent. That speed varies by make and model, but according to David L. Greene, a corporate research fellow at Tennessee’s National Transportation Research Center, “there would be very few cars with an optimal speed above 70 mph.” Still, an autobahn limit might not be a huge help. Even now, its drivers average around 80 mph.
—Tom Zeller, Jr., National Geographic, October 2007