The main force reducing mileage is air drag, says Dr. Greene. The faster you go, the greater the drag. Drag forces increase exponentially, so doubling your speed from 40 to 80 increases drag fourfold.
It makes a huge difference, for at 80 m.p.h. your car pushes against wind with the force of a hurricane.
Consumer Reports tested the effect of higher speeds on gas mileage. David Champion, director of auto testing, found that boosting the highway speed of a 2006 Toyota Camry cut gasoline mileage dramatically:
•55 m.p.h. – 40.3 miles per gallon
•65 m.p.h. – 34.9 miles per gallon
•75 m.p.h. – 29.8 miles per gallon
On a hypothetical 1,900-mile round trip from New York City to Disney World in Florida, the Camry would use 47 gallons of gas at 55 m.p.h.. But at 75 m.p.h., it would burn nearly 64 gallons – a $70 difference.
Tell that to the pushy raised pick-up trucks with yellow ribbon magnets that try to run me off the road on a near daily basis.