The invention relates to a method for calibration of a road surveillance system (1). Said road surveillance system (1) is adapted to monitor a surveillance area (8) of a road (15) and comprises a plurality of vehicle surveillance means. Said plurality of vehicle surveillance means are adapted to measure a position of a vehicle passing said surveillance area (8) and are synchronized with a global timing signal. The method comprises, in order to calibrate said plurality of vehicle surveillance means such that a position determination of said plurality of vehicle surveillance means is equal, passing a calibration vehicle (5) through said surveillance area (8). Said calibration vehicle (5) is provided with a plurality of predefined calibration markers (6). Said calibration markers (6) are provided at predetermined positions upon said calibration vehicle (5). During the passage of said calibration vehicle (5) through said surveillance area (8) each measurement means measures a position of an assigned calibration marker wherein said measuring is performed at a predetermined time and compares a measured distance between the positions of said calibration markers (6) with a reference distance between the positions of said calibration markers (6) and calibrating said plurality of vehicle surveillance means such, that the measured distances between the calibration markers (6) correspond to the reference distances between said calibration markers (6).