A system for monitoring road traffic flow on a roadway 1 comprises a central control unit 30 for deployment near a roadway and multiple roadside detection modules 20. Each detection unit is operable to monitor a traffic flow parameter (e.g. using RADAR or LIDAR); generate an alarm condition in dependence upon a monitored traffic flow parameter and a predetermined alarm condition; and consequently transmit 31 traffic flow parameter information to the central control unit. The central control unit may include a camera such that an image of a portion 2 of the roadway may be captured and transmitted 32 with the flow information to a recipient. Transmission 31, 32 may be wireless. The central control unit and detection module may be lightweight for ease of transportation and temporary deployment, e.g. to monitor traffic near road works.
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