A method and apparatus is disclosed for evaluating the driving of a vehicle performing a journey on a road network, comprising determining at least one constant speed zone of the road network, a constant speed zone being a portion of the road network at which the vehicle can travel at a constant speed, said determination being based upon expected speeds of travel along the road network determined from positional data relating to the movements of a plurality of vehicles over time along the road network. A speed of the vehicle traversing the road network is determined at a plurality of times during the journey, and a value indicative of a consistency of the speed of the vehicle within the at least one constant speed zone is further determined.