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.