Joo Koon collision: Software glitch in signalling system results in second train misjudging distance

Two MRT trains collided at Joo Koon station on Wednesday morning, injuring 29 people. Here are five things about the accident.
Two SMRT employees and 26 commuters were injured in the collision.
Two SMRT employees and 26 commuters were injured in the collision.PHOTO: MELVIN LAU
SMRT staff inspecting an affected train on platform B after 2 trains collide at Joo Koon MRT station on the morning of Nov 15, 2017.
SMRT staff inspecting an affected train on platform B after 2 trains collide at Joo Koon MRT station on the morning of Nov 15, 2017.ST PHOTO: SEAH KWANG PENG
Rail officers inspecting the trains.
Rail officers inspecting the trains.ST PHOTO: JONATHAN CHOO
The second train stopped 10.7m behind the first one as the glitch caused it to "misjudged the distance".
The second train stopped 10.7m behind the first one as the glitch caused it to "misjudged the distance".ST PHOTO: JONATHAN CHOO
Stranded commuters at Joo Koon station after the collision.
Stranded commuters at Joo Koon station after the collision.ST PHOTO: JONATHAN CHOO
The stalled train at Joo Koon was mistakenly profiled as a three-car train instead of a six-car one, causing the second train to "misjudge the distance".
The stalled train at Joo Koon was mistakenly profiled as a three-car train instead of a six-car one, causing the second train to "misjudge the distance".ST PHOTO: JONATHAN CHOO

SINGAPORE - An unprecedented software glitch in the signalling system of the East-West Line resulted in a collision between two MRT trains at Joo Koon station on Wednesday morning (Nov 15).

This resulted in a stalled train at Joo Koon being mistakenly profiled as a three-car train instead of a six-car one in the system, operator SMRT and the Land Transport Authority (LTA) revealed.

As a result, a second train which stopped 10.7m behind the first one "misjudged the distance" between the two, resulting in a collision, and injuring 29 people.

Transport Minister Khaw Boon Wan said: "It's an awful day today. Commuters were inconvenienced, and some even injured. We are deeply sorry for that."

Sharing their preliminary findings at a press conference on Wednesday evening, SMRT and LTA said the first train departed Ulu Pandan depot with a software protection feature, but this was "inadvertently removed" when it passed a faulty signalling circuit.

When it arrived at Joo Koon at 8.18am, all passengers were detrained due to an anomaly in the train signalling system, except for one SMRT staff member on board.

At 8.19am, the second train, carrying more than 500 passengers, arrived but stopped at the correct safe stopping distance, said LTA and SMRT. However, a minute later, the second train moved towards the first train and hit it.

Among the 29 people hurt were 27 commuters, and one SMRT employee each on board the first and second trains.


Transport Minister Khaw Boon Wan said that the investigation should be allowed to take its course. ST PHOTO: BENJAMIN SEETOR

Thales, the company which is supplying the new signalling system for the North-South and East-West lines, said it had not encountered a glitch similar to Wednesday's incident previously.

Said Mr Khaw after the press conference: "Thales is confident of their system, but I advised the team, let's play doubly safe, where safety is involved, that's why I want them to suspend the Tuas West Extension tomorrow, so we have a whole day to do a thorough check before we resume the Tuas West Extension."

Asked if a committee of inquiry will be convened to look into this, Mr Khaw said the investigation should be allowed to take its course.

Asked whether commuters' confidence in the MRT system had been undermined following Wednesday's accident and October's MRT tunnel flooding, Mr Khaw said: "Obviously people will be upset... I'm equally upset."