Broken signalling cable led to six hour disruption on Downtown Line

A broken signalling cable has been identified as the cause of delays that lasted for about six hours on the Downtown Line (DTL) on Monday, 28 December 2020.

Commuters had faced longer travelling times along a stretch of 12 stations from Expo to Geylang Bahru during evening peak hours, from around 6:30pm. The fault continued till the end of service hours, past midnight.

Rail operator SBS Transit had said that the fault caused delays of up to 20 minutes, although commuters said they experienced longer delays.

In an update on Thursday, 31 December 2020, SBS told The Straits Times that the fault originated at a sector between Mattar and Geylang Bahru stations, in the direction of Bukit Panjang.

The signalling system's safety protection measures automatically kicked in and imposed a speed restriction of 18km/h for trains travelling over the affected track section. SBS Transit Senior Vice-president for Corporate Communications Tammy Tan said, "Our engineers responded to the situation by employing the established recovery procedures recommended by Siemens, the original equipment manufacturer. However, they were unsuccessful in recovering regular passenger service despite several repeated attempts."

Ms. Tan said SBS engineers found the broken signalling cable between Mattar and Geylang Bahru in the early hours of the morning. This cable had affected the transmissions of signals in the system. The cable was replaced and trains travelling through the sector were able to resume their regular speeds of 70km/h by the start of operations on Tuesday.

Ms. Tan said, "SBS Transit together with the Land Transport Authority have discussed with Siemens to provide an action plan to expedite the recovery of normal train operation in the event of such a situation and to prevent future occurrences."

Signalling systems are used to direct rail traffic and ensure a safe distance between trains. The DTL service disruption was the second major signalling fault along an MRT line last month.

On 4 December 2020, Thomson-East Coast Line services were disrupted for five hours because of a software glitch in the signalling system's network component.