From the Red Line
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From the Red Line

Getting the bends

Some old maps show an extension of the NEL from Punggol towards Seletar. Did it actually exist?

I’ve tried to put together as much information as I can find in the public domain (or, at least, that one can pay money for). But the issue around this is that different sources say different things. What use would there have been for such a tunnel? This might all be moot considering that the NELe takes a rather different alignment in order to head to Punggol Coast, but it might still be worth examining.

Schrodinger’s tunnel

If you go to onemap, you’ll see this alleged curve right there, with the NEL making a 90 degree turn under the Punggol Waterway to align to what is now Seletar North Link.

onemap retrieved 3rd July 2022

Even the LTA’s commemorative book on the construction of the NEL also shows a similar alignment. Consequently, Streetdirectory and other third-party map makers may have taken it as gospel as well. But yet URA Master Plans are silent on its existence, which logically should mean land wasn’t set aside for this tunnel. The 2014 URA Masterplan shows the tunnels extending to only around 200m after Punggol station at most.

URA MP 2014

While one can say that this might have been a cartography mistake by the URA, it roughly matches up with satellite images of the construction site taken from Google Earth. There’s a bit of a gap between the end of the URA Masterplan-defined alignment and the start of the cut and cover tunnels worksite, but perhaps it can be assumed that the missing area was also built at the time of NEL construction — though I wouldn’t say for sure without satellite images from that time, which I have been unable to source.

NELe worksite left of the LRT track

Likewise, the length and extent of cut and cover works shown in the satellite image also aligns with the LTA’s prior claims that 120m of this tunnel will be built in a cut and cover manner. The launch shaft for the remaining 710m of bored tunnel is presumably under the sheltered structure somewhere in the middle of the site.

Official statements likewise do not seem to indicate that there are existing tunnels that must be removed before the new tunnels can be built. This is backed up by Google Earth imagery of the Circle Line tunnels near Promenade, where the excavation has to follow both the new and old tunnel alignments; the old partially-built tunnel having to be abandoned after the Nicoll Highway collapse. Compare this against the NELe worksite shown above, where pretty much only the new tunnels are excavated.

Satellite imagery near Promenade station

If they had planned to build the tunnel so far out, what could it have been for? Even in the same book (Tunnelling and Underground Space Technology volume 14, 1999) I can find two different answers. For copyright reasons I won’t reproduce the images and can only describe what I see in them, but it’s in the book if you can get access to it.

  • A paper by Hulme and Burchell (from page 409) shows the overrun extending in a slope way past Punggol station.
  • Another paper by Krishnan, Copsey, Algeo and Shirlaw (from page 433) shows a truncated overrun ending much nearer to Punggol station
  • A paper by Reilly (page 491) shows the same map as the paper from page 433

I’m inclined to think the second map shown in the Krishnan, Copsey, Algeo and Shirlaw paper is a newer one more matching the as-built conditions of the NEL — namely, that newer names like Little India and Potong Pasir are used instead of Kandang Kerbau and Sennett. Perhaps they might have planned to build it at first but then changed their plans later on.

That said, though, the earlier map shows longer tunnels ending just before some kind of ground depression, which could represent where the shoreline used to be before land reclamation activities took place to shape out the Punggol we know today. So it’s very likely that that extension would have been where the curve would have been.

What was it for?

Early plans for the NEL led it to both Punggol and Jalan Kayu — though what the maps then called Punggol might correspond to contemporary Sengkang or even Buangkok or some other point south. Well, obviously, this didn’t happen.

Since people think branching is bad, especially for a line like the NEL designed to operate at high frequencies, I can’t help but think that instead of some kind of branch line from Serangoon or something to Jalan Kayu, a hook-shaped extension might have been proposed, where trains first go to Punggol then the Jalan Kayu/Seletar area — that later bit perhaps to be left for a future stage of the NEL.

But those plans might have been scrapped when the idea to build a North Shore Line came about, first mooted in the 1996 White Paper as a line from Sembawang to somewhere near Punggol. The same map also shows the NEL extending to Ubin and Tekong instead, so take from it what you will. But with a newfound awareness for natural preservation these days, and the logistics of living on other islands, I don’t think this might happen.

Because of this new line, perhaps digging deeper at Punggol station to construct the provision box now to be used by the CRL Punggol Extension could also have underlined the futility of the extended tunnel. With a new line coming this way and transfers to the new line possible for those going to Seletar/Jalan Kayu, it may not be necessary for the NEL to make such a dramatic hook turn, which meant the overrun could be potentially be cut back to save money.

Much ado about nothing, perhaps

There may be another, not so sexy reason, but I think this is much less convincing than a cartography error.

It might have been possible that the extended alignment actually existed at some point in the past. But only as a construction staging area during the period of NEL construction, with tracks aboveground being used to load up construction material such as tracks and other tunnel infrastructure before ramping down into the tunnel. But this is unlikely, considering the proximity of the NEL depot.

Example construction staging area at TEL Mandai Depot

For a comparable project, the TEL construction staging areas for the respective stages were at:

If it was possible to support the construction all the way to Woodlands North from Mandai Depot for TEL1, it might probably have been possible to support construction and tracklaying at Punggol MRT from the NEL depot as well, negating the need for an additional site in Punggol.

How could these be on the map? A 2010 map archived by NUS’ Geography Department shows a similar stub near Expo station, but satellite imagery from around that time shows some cleared land. The stub also exists in a paper written on the construction of the Changi Airport Line tunnels, so it’s quite possible that the Expo stub was meant to support the construction of the extension — not for operations, considering how near the existing Changi Depot is.

That’s weird (sources in images)

Given how that site sits on where the Singapore University of Technology and Design now is, the temporary worksite may have been drawn by the cartographers for some reason or another when drawing the map earlier, and it just remained there. Someone might have checked on it when construction began on the SUTD campus, but without maps after 2010 on the NUS website I won’t want to be too sure.

Simpler explanations

We may never know for sure whether the bend in the NEL tunnel really existed without the opportunity to access the LTA archives, but after reviewing what publicly available evidence I can find, I’m inclined to think it didn’t exist.

There probably wasn’t much need for it either considering that the crossovers are before Punggol station, unlike at HarbourFront where trains reverse after the station during peak hours and extending the overrun track was necessary in order to allow faster train operation speeds. Likewise, the proximity of the depot to Punggol means that there’s not such a need for so many space to store broken-down and spare trains as they can be sent to/from the depot.

At least the non-existence of such a tunnel made it easier to consider extending the NEL outward to Punggol Coast, doing the job of the presumably-cancelled Punggol North LRT. Punggol Coast also offers a similarly long 300m overrun track, which may not be that much of a reduction in performance compared to the existing tracks.

Likewise, perhaps the construction of Punggol Coast might allow for further increases in NEL service level similar to why the Pasir Ris overrun rebuild happened — considering that the track layout in the Punggol area is similar to that of Pasir Ris. The NEL may be automated, but I won’t be surprised if we were touching the limits of said automation due to the built infrastructure; if it were regular straight track, the extended tunnel wouldn’t have helped anyway.

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yuuka

yuuka

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