From an article in Consumer reports –
Slow down. In our tests, we’ve found that driving faster on the highway can really take a bite out of a car’s fuel efficiency.
We measured gas mileage while driving at a steady 55, 65, and 75 mph in a Nissan Altima and Toyota RAV4. Reducing speed from 65 mph to 55 mph improved fuel economy by 6 mpg in the Altima and 8 mpg in the RAV4.
The penalty of cruising at 75 mph, rather than 65 mph, was almost 7 mpg in the Altima and 6 mpg in the RAV4.
These findings are similar to what we have recorded in the past, once again proving that higher speeds exact a toll in fuel consumption.
Another way to look at it: Speeding up from 55 to 75 mph is like moving from a compact car to a large SUV. Beyond fuel concerns, speeding is, of course, a safety risk as well.
Avoid hard acceleration and braking whenever possible. In our tests, frequent bursts of acceleration and braking reduced an older Toyota Camry’s mileage by 2 to 3 mpg. Once up to speed on the highway, maintain a steady pace.
The harder you accelerate, the more fuel you use. Unnecessary braking wastes the fuel you used to get up to speed. Drive smoothly and anticipate the movement of traffic. Once up to speed, maintain a steady pace. Smooth acceleration, cornering, and braking also extend the life of the engine, transmission, brakes, and tires.