a system for determining an energy - optimum route for a vehicle to take between an origin and a destination includes a computer onboard the vehicle . a global positioning system transceiver is also onboard the vehicle for receiving vehicle position data from the satellite . the computer access a database containing both topographical map information and vehicle energy consumption data , and based thereon the computer determines and displays an energy - optimum route . the computer can also display information regarding nearby refueling stations . also , the vehicle energy consumption data can be modified as appropriate based on the operation of the vehicle , to account for the particular vehicle &# 39 ; s actual fuel consumption characteristics .