A system and method of adding one or more sensors to a road traffic monitoring network includes providing one or more sensor arrays of wireless road-based sensors mounted on, in, or at a surface of a road network, each sensor array including at least three sensors, analysing sensor measurements to determine traffic information including vehicle speed information, identifying from the sensor measurements that one or more sensors have become separated from the road or are otherwise malfunctioning, adding one or more sensors to replace or supplement the one or more sensors that have become separated from the road or are otherwise malfunctioning, and using analysis of received measurements to associate the one or more added sensors with an existing sensor array to restore or maintain redundant operation of the sensor array.