Was system upgrade to blame for signal failure that caused six hours of chaos on Hong Kong rail network?
Four lines share one ‘main brain’ and work on Tsuen Wan route may have affected Island, Kwun Tong and Tseung Kwan O lines
The reliability of the signalling system on Hong Kong’s railway has been called into question after it broke down on four of the city’s lines and caused six hours of chaos on Tuesday morning.
During the morning rush hour, MTR services on Island, Kwun Tong, Tsuen Wan and Tseung Kwan O lines were disrupted by a fault, that affected hundreds of thousands of commuters on their way to work, and school.
Hours after normal service resumed, the MTR Corporation said it would form a committee to investigate the matter, and invited external experts to take part.
Hung Wing-tat, a fellow of the Hong Kong Society for Transportation Studies, said signalling faults were common to see, “sometimes [these are] caused by some buttons getting old, or sometimes due to it [the signalling] being overly sensitive”.
“Similar problems also happen to other systems in the world. The key is how to control it within a tolerable level,” he said.
Large-scale breakdowns have also raised questions in the management of the Mass Rapid Transit (MRT) network in Singapore.
1. How does the signalling system in Hong Kong MTR work?
According to a Legislative Council document in 2016, the signalling system is the hub of the railway operation. It controls train operation, and will bring trains to an automatic halt if any irregularities are detected.
The Tsing Yi Operations Control Centre captures the operation status of the system via the data transmitted through the monitoring and communications system.
Former railway boss Michael Tien Puk-sun said the affected lines were linked under two signal systems which are connected to each other.
“The affected lines were all controlled by one main brain,” he said. “Therefore, in this case, when one line got a problem for an unknown reason, the other three lines were affected.”
2. What are the advantages and disadvantages of the existing arrangement?
Tien, who is also the chairman of the Legislative Council’s railways subcommittee, suggested that sharing one system provide a greater flexibility, allowing trains to transfer between lines.
But, the downside was when a problem occurred, several lines would be affected as they were bundled together.
The rail firm said it would investigate whether the signal glitches on Tuesday were caused by the upgrade of the Tsuen Wan line’s signal system on Monday night.
Tien said the operator should be “very careful” in stepping up the systems on the four lines, because “similar problems may happen”.
Hung said the rail operator should know there was a risk in upgrading the system of one line, because the four lines shared tracks in some sections.
“When a signal from one system failed to control the trains on one line, it would affect others because they couldn’t receive signals on when a specific train would arrive,” he said.
3. What should the MTR Corp do better?
Apologising to the public, MTR Corp managing director Jacob Kam Chak-pui said the breakdown of four rail lines in one day was so unprecedented that even the design and maintenance handbook did not mention such a scenario.
The problem on the service were “complex”, and the MTR Corp had to download relevant data for analysis after train services finished for the day on Tuesday, Kam said.
A Facebook page called MTR Service Update said initial information suggested the breakdown had been caused by re-signalling works. An MTR Corp staff member who helps runs the page, but wished to remain anonymous, said there were some problems with the corporate data network.
The page, which has more than 56,000 followers, shares information on railway service incidents.
Staff members suggested that programming verification should have done better, for example making sure there were no bugs in the system, as to make the process work smoothly.
4. What are overseas experience in rail systems such as those in Singapore?
In Singapore, rainwater flooded a metro tunnel and caused disruption to parts of the rail network for about 20 hours last October. A mechanism designed to remove storm water from the tunnel failed to work as it was poorly maintained.
Transport minister Khaw Boon Wan criticised workers in charge of anti-flood measures at the metro operator, adding the maintenance team had “failed us”.
A new signalling system had also caused several minor delays.