A CLOSED-CIRCUIT television system that can detect suspicious behaviour is being tested this week at two London Underground stations.

The Intelligent Pedestrian Surveillance system, being piloted at Liverpool Street and Mile End stations, is designed to spot passengers who may be about to attempt suicide or commit a crime, or to detect overcrowding before it becomes dangerous. The computerised network uses advanced software to track unusual movements and alert staff if abnormal patterns are detected.

While existing CCTV can be used to do this, it is only as good as the operators who watch the images. Often there are too many cameras for the human eye to follow: London Underground staff can have as many as 60 cameras to monitor simultaneously.

The number of CCTV cameras in Tube stations in London is set to increase from 6,000 to 9,000 over the next few years, and cameras are also being installed on trains.

Peter Tollington, who is overseeing the installation of the system, told New Scientist magazine: “CCTV itself is fantastic, but this puts it on another plane. It means that you don’t have to look at a screen all the time.”

Six European countries collaborated on the system, which took ten years to develop. Actors were used to simulate passenger behaviour in London Underground stations.

The software compares images from each camera with pictures of the empty station, and clusters of pixels that differ between them are tracked in real time. For instance, an image that remains on a platform after several trains have passed could be a loiterer, someone who is lost or a potential suicide victim.

The system does not distinguish between the possibilities, but draws attention to the need for something to be investigated.

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