If you drive at 55 mph rather than 65 mph, you can improve your fuel economy by as much as

Tractor-trailers today average about 6.5 miles per gallon of diesel fuel. Driving at 55 mph rather than 65 mph can increase fuel economy by as much as one mile per gallon. That works out to a saving of about two gallons of fuel for every 100 miles traveled. Over the course of a year of driving, that can add up to significant savings.