London Congestion Charge OCR technology (Anders Jacobsen's blog)

January 11, 2005

London Congestion Charge OCR technology

Curious visitors looking for information on "congestion charge ocr", here you go:

The London Congestion Charge zone is a defined area in London where you have to pay a fee to drive your veichle. The charging of this fee (and the tracking of evaders) is being done by a large number of CCTV-style cameras, of which most (688 total (254 colour, 434 mono) cameras)) are installed at 203 camera sites at the edge and inside the zone, recording streams of video of roads in the zone. There are also ten mobile camera units which may be deployed anywhere in the zone (and are moved randomly).

Wikipedia tells us:

The video streams are [...] transmitted to a data centre located in Central London where a computer system equipped with Automatic Number Plate Recognition (OCR) software deduces the registration plate of the vehicle. A second data centre provides a backup location for image data.

Although this process is not infallible, the process only needs to have a reasonable probability of success to have a deterrent effect. It appears that both front and back number plates are being captured, on cars going both in and out. This gives up to four chances to capture the number plates of a typical car entering and exiting the zone.

I haven't found tech specs for the CCTV/OCR technology itself, but it may not be vastly different from what is called Automatic Number Plate Recognition (ANPR) - a portable image-regonizing license plate alert system used by british police forces to quickly identify stolen/uninsured cars.