While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 60 mph. In general newer cars maintain peak fuel economy to higher speeds than older models.

Optimal efficiency can be expected while cruising with no stops, at minimal throttle and with the transmission in the highest gear.

You can assume that each 5 mph you drive over 60 mph is like paying an additional $0.26 per gallon for gas. Drivers of vehicles with fuel-economy displays can check their own vehicles by cruising at different speeds and monitoring the readout.