1. A computer implemented method for determining a length of a route travelled by a vehicle using a position measuring device that records positions of the vehicle, and a digital road map including road segments of known segment lengths, the method comprising: recording positions of the vehicle on the route by the position measuring device; matching the recorded vehicle positions to a sequence of road segments travelled by the vehicle, by a processor; calculating by a processor, from an angle between two consecutive travelled road segments of said sequence of road segments and an assumed road width of the two consecutive travelled road segments, a turn-off route length travelled by the vehicle from the first consecutive travelled road segment into the second consecutive travelled road segment of the two consecutive travelled road segments; and determining the length of the route travelled by the vehicle from segment lengths of the sequence of road segments travelled by the vehicle, and the calculated turn-off route length travelled by the vehicle.