The Changi Problem
I thought this deserved a post by itself.
In the latest masterplan, it was announced that the Changi Branch of the East West Line will be transferred to the Thomson-East Coast Line. There are, of course, a few issues with this.
In my previous post, I mentioned:
Of course, this is assuming they’ve managed to solve the problem of Changi Airport T1/2/3 station platforms not being able to accept the 5-door TEL trains. In short, the station’s supports are designed in such a way that pairs of doors on the NSEWL fleet are aligned with gaps in the supporting pillars. On the TEL, this means that the middle door will just open into the tunnel wall, creating a safety risk. One such way to do that is selective door operation such that the middle door doesn’t open at all, but that’s a band aid at best.
But what is this “Changi Problem” in the first place, and why bother at all?
2024 update: Nothing in this blog post has changed. It appears the LTA will press forward with this project, so let’s see how they plan to work around things.
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This sounds like a headache
Yes, it does, and we’ll see why later. But if you ask me, the LTA has been clear that the intention is to provide direct travel between the CBD and any airport terminal.
Currently, the Changi branch line service doesn’t do this. There was a while in the early 2000s when they did, even down to fitting C751B trains with luggage racks for airport-bound travellers. However, the through service was quickly canned due to low ridership, and that most people were going in the direction of Pasir Ris.
But today, with the Downtown line, the development of Changi Business Park, and of course Jewel, I daresay things are quite different. In fact, sometime early last month I went to Jewel to soak up the hype, and Changi Airport station was the busiest I’ve seen in quite a while. It’s clear that better train services are needed.
In the short term, with the extension works at Pasir Ris, they may be unable to send so many trains in that direction. As a consequence, it may become possible to send some direct trains to Changi Airport, but it probably won’t work out after the works at Pasir Ris are done, when the opportunity comes to send more trains in that direction again. Hence the transfer of the Changi Branch to the TEL, which can provide better service (think a train every 2 minutes instead of 8), albeit with smaller trains, and still retaining the direct service from the CBD, although it’s a longer distance via the east coast.
What is *not* the problem
Let’s get this out of the way first.
I expect the TEL to connect to the existing Changi Airport station overrun tunnels under Terminal 2. If you consult onemap the tunnels are shown ending just before gate E20, so it won’t be a big issue to dig a hole there for the TBM to reach.
Signalling isn’t a problem, since it’s just a matter of installing the new system over the old one. LTA’s done it before, it may have almost been a trainwreck but the concepts and experience are there. It might seem like a waste of money to set up and signal the Changi Branch again so soon, but well…
Power isn’t the problem either, since both EWL and TEL use a third rail system. They will want to split out the Changi Branch power supply from the EWL one, though, and that might incur some downtime. But I don’t think it will be that hard.
The track layout isn’t an issue too. Part of the construction of that mega 3 in 1 depot in the East Coast will build new tracks for the EWL, so that the Changi branch is no longer constrained to a single track. In fact, this is actually a remnant of the original plan to run through service from Boon Lay (then the EWL terminal) to Changi Airport, but that didn’t really work out due to low ridership.
Don’t fall off
In a way, the platform doors are the problem. But it’s at the same time much easier and much harder than you think.
I’ll have to let this picture speak for itself.
The green block is an EWL train, brown block a TEL train. Where I’ve put black lines indicate PSD panels, and on the green and brown blocks, train doors. See the blue rectangle? That’s a structural support pillar holding up the station structure. And it’s in the way of door 3.
What this means is that besides the obvious reconfiguration of PSDs to ensure that the platform doors line up with the TEL trains, there is also a need to find a way to deal with that support pillar. If the train doors just open like that into the tunnel, unsuspecting passengers could meet the fate of Wile E. Coyote. And I’m sure no one wants that.
One way, as mentioned, is to use selective door operation, such that door 3 remains closed while all other doors open into the platform. However, this would require in-train notices and reminder announcements, given that this is an airport station we’re talking about and plenty of passengers are new to the MRT network. Also, systems aren’t perfect, and what if the selective door operation controls fail?
Another is to cut away the pillars and provide a continuous platform. I’d argue that the LTA has the full documentation of the station’s structural support system, and they would be best placed to find a way to do it. However, I’m still thinking that whatever method they choose to cut the , I would expect a few weeks’ closure of Changi Airport station, in order to allow for the pillars to be safely cut and removed while temporary supports hold the structure up. Don’t forget there’s a bridge in the middle of the station hall that restricts the amount of space available for such works. And, of course, whether relevant approvals in the name of safety can be obtained for such works.
Of course, alternatively you could throw everything out and build a new station for the TEL at terminals 1/2/3, while leaving the Changi branch untouched, or even extending it to T5, giving you 2 MRT lines between the terminals. London Heathrow has this with the Piccadilly Line and TfL Rail (soon the Elizabeth Line), and Tokyo Haneda also has the monorail and Keikyu trains. Then again, this would cost a lot more, and I’m not really sure where such a new station would go. (maybe nearer to T1 and Jewel?)
Where else?
There are plenty of other places where this happens too, although they’re all on the NEL and lines built after that. It’s too long a list to fully describe, but Dhoby Ghaut and one-north on the Circle Line are particularly egregrious examples — especially since you could argue that the Circle Line, as an orbital line with high passenger traffic at interchange stations, would need 5 door cars the most.
As an example, look at the picture below, of Dhoby Ghaut’s CCL platforms. There’s a pillar between every door. An undertaking like what they plan to do at Changi would require a redesign of the entire station.
Hopefully Changi Airport will be the first and last time we have to do such technically complex projects. For future capacity increases, one thing to consider would be keeping the door positions as is, but widening them so as to provide a similar door capacity increase as adding a 5th door position. Something like the Tokyo Metro 15000 series.
However, it’s important to note that the platform doors themselves are also built with a degree of tolerance to allow for trains stopping in irregular positions (I’m told this is about +/-200mm off the stopping mark). Making the train doors wider will reduce this tolerance, which may reduce some of the passenger benefit of having wider train doors, although they could of course modify the platform doors as well. Wider doors also take longer to open and close, too.
