Abstract: An apparatus and method for monitoring traffic comprises a plurality of vehicles fitted with units. Each unit comprises a CPU, a timer and a GPS device. Whenever a vehicle passes a waypoint determined by the GPS device, the CPU notes the time supplied by the timer. When the vehicle passes the next waypoint determined by the GPS device, the CPU notes the time again. The CPU substracts the two times to derive the actual journey time for the link between the two waypoints, and this is compared against a stored link-time for the link. If the actual journey time is greater by a preset amount than the stored link-time, then the unit transmits the relevant information to a control computer by way of a communication device. In addition to notifying the control computer when the vehicle has exceeded a standard time for the link between the waypoints, the unit can monitor the progress of the vehicle along the link by monitoring its progress along sublinks using a technique known as “micro-pointing”.