A new system using infrared detectors to monitor traffic movements and control traffic lights is being tested at three junctions. Transport officials hope they can replace the existing, more costly system, which uses wires embedded under the road. A senior engineer at the Transport Department, Wong Wing-kwong, said the detectors had been installed at the junctions of Tat Chee Avenue and Dianthus Road, Kowloon Tong, Choi Hung Road and Tseuk Luk Street, Wong Tai Sin, and Collinson Street and Kennedy Town Praya, Kennedy Town. The German-made devices, fitted on the top of traffic lights, were installed between April last year and last month. More than 800 detectors using the embedded wire system, with what are known as inductive loops, are buried under Hong Kong roads. Mr Wong said the inductive loop system could disrupt traffic during installation and repairs. 'Repair of damaged loops is costly because works to dig under the road is needed,' he said. 'Since the detector can be mounted on the top of a traffic signal, disruption to traffic and costly engineering works can be avoided.' An infrared detector costs only $10,000, while it costs $30,000 for the hardware and installation of an inductive loop. But test findings on the infrared detector installed in Kowloon Tong showed it was sometimes only between 85 and 100 per cent reliable. 'Results showed that if a jay-walker stepped in its detection zone it may count him as a vehicle and tell the traffic signal ahead to switch to the green light signal,' Mr Wong said. He said their initial observation was that the detectors were more suitable at junctions of a minor road and a main road, where rails prevented people from walking across the road recklessly or illegally.