While the use of automatic number plate recognition (ANPR) to provide journey time information has been a valuable addition to the overall traffic management strategy of Essex County Council, experience shows that optimumuse is only gained when a solid understanding of the capacity of the system, as well as any limitations, is known. The experience in Essex demonstrates the importance of careful planning prior to implementation. The system provides real time monitoring of routes for day-to-day traffic management and incident detection, as well as long-term monitoring of the network for performance analysis. The primary challenge of journey time monitoring with ANPR is obtaining a high match rate of vehicles between the camera pairs whilst minimising the physical number and optimising the location of cameras; factors which limit the match rate are also discussed. This paper describes the challenges that Essex has faced and how they have been addressed.
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