If you’re one of the many drivers who typically go anywhere from 5 to 15 mph over the speed limit, Consumer Reports has looked at the fuel economy penalty that you’re giving yourself. The publication wanted to know if you drive at 75 mph rather than 55 mph, how much additional fuel would be used.
The publication looked at several vehicles including the Honda Accord LX 4-cylinder. With the Accord, the fuel efficiency decrease between 55 and 75 mph was 29%. CR says that by driving 200 miles at 75 mph instead of 55 mph you’re losing approximately $30 and increasing your carbon footprint by 7 to 10 gallons.
At 75 mph the Accord averaged 35 mpg. At 55 mph, the Accord averaged 49 mpg. These fuel efficiency ratings sound really high to me it would likely vary significantly from most drivers.