A method and apparatus for evaluating an advised driving speed of a vehicle traversing a particular portion of a road network is disclosed. The method comprises accessing first predetermined data indicative of the variation in average fuel consumption for the vehicle with speed of the vehicle, using the first predetermined data to determine data indicative of average fuel consumption for the vehicle for a plurality of speeds within a range based on a speed limit for the portion of the road network being traversed, and evaluating the advised driving speed of the vehicle based at least in part on the determined data indicative of average fuel consumption for the vehicle for the range of speeds. The evaluation of the advised driving speed may further be based on second predetermined data indicative of the variation in a likelihood of the vehicle being in the highest gear with speed of the vehicle.