From the Red Line
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From the Red Line

Automatic train what — ?

I was asked about this a while back, when there were all sorts of issues along the NSL.

“But SMRT claims that they’re automating the NSEWL, that’s why all these problems are happening!”

Well, no, that statement isn’t incorrect, but it’s not entirely wrong either. As usual we don’t know the whole story, so let’s look at it this week.

The bad old days of Westinghouse Fixed Block

The old Westinghouse block system installed in the 80s has plenty of components, but we’re only interested in two: ATP and ATO.

ATP, short for Automatic Train Protection, is the feature that physically prevents a train from colliding with another one in front of it. Imagine if you had a device in your car, that could read traffic lights, and prevent you from running a red light.

In London and New York, since systems are older and far more crude, there are physical devices that can trip the emergency brake of a train when it runs a red signal. We don’t have such things in Singapore — the train’s onboard computers must read the signals off the track.

This is what caused the Clementi train crash of 1993, which happened almost 24 years ago to the day. Then, due to oil on the track, the train’s onboard computers were unable to interface with the signals being transmitted on the track, failed to see the other train in front of it, and ploughed directly into the front train.

The second, less critical part is ATO, or Automatic Train Operation. In Singapore, ATP does not only transmit instructions to “go” and “stop”, it also transmits instructions on how fast you can go. Like the autopilot of a commercial airliner, ATO reads these codes from the ATP system, and goes as fast as it is allowed to, within the speed limits defined by the codes. This is why, when on the EWL, you may see cases of trains slowing down, and speeding up again.

ATO is started by the driver pressing two buttons in his cab to depart. There is a light on the front of every train, and this light is turned off when the ATO system is in use. After all, ATO is the preferred mode of operation as it guarantees some consistency in performance.

However, this does not mean the driver has no control of the train. He can take over manual control of the train, while subject to the same ATP speed limits as the ATO system, or he can have the train ignore the ATP codes, but for safety reasons, he is limited to 18km/h. When he does so, the light at the front of the train turns on.

Hence, in normal operations, the driver only watches the doors, and regular movement of the train is controlled automatically unless it’s raining.

From Paris, with love

When the North-East Line was designed in the 1990s, it was thought that it would be a good idea to adopt the then-new and highly advanced driverless train technology, the first early adopter being Line 14 of the Paris Metro that opened in 1998.

This completely took away the driver from the equation, allowing a train to manage itself completely automatically, and was then the longest line in the world to do so. A fully-automated CBTC-based signalling system was then an unproven technology, but LTA’s bet paid off, and the NEL is running on technology that has only been picked up by metros today.

It proved so successful, in fact, that the decision was taken to also employ automated, driverless technology on the then under-construction Circle Line, and every MRT line after that. But what about the NSEWL?

A proposal was floated early in the 21st century to install a modern signalling system on the NSEWL. But, as I think we would all know, the then-SMRT CEO didn’t bother with that, choosing instead to take a leaf out of the book of Japanese railway firms, and invest in shopping and property around stations. And for that, we now pay the price, and have to make up for it plus interest in the form of disruptions.

So why is there still someone in front?

Unlike the other MRT lines, which are all underground and safely protected from the elements, the NSEWL have significant overground stretches, where it’s exposed to Mother Nature.

Under the old Westinghouse system, train drivers were required to drive manually in inclement weather, since slippery rails meant that the crude braking of the ATO system could often cause trains to miss stops. And as we saw during the CBTC testing, even under CBTC which by right should allow for more fine-tuned control of how trains brake, some work is still needed.

Also, the driver is there to take control, should he be needed. Should there be a failure in the CBTC communications systems, like what happened last year along the Circle Line, the driver can still take control of the train and keep a service running. This is also why, on the other lines, there’s always one member of staff near the front of the train, even if he doesn’t seem to be doing much.

Hope that answers some doubts. Questions and comments welcome.

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yuuka

yuuka

Sometimes I am who I am, but sometimes I am not who I am not.