Why is Promenade Station on the Downtown Line so deep?
Before we start, I must apologize for the lack of Downtown Line-related posts recently. Not only have I recently started a new job that may take away time I’d love to use to write, but too many things have also happened on other parts on the network, and I felt it more apt to discuss the current affairs as compared to a relatively niche and unpopular topic like station design.
To understand why Promenade Station is the way it is, we must go back to 2004, to the sad tragedy of the Nicoll Highway collapse.
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At first, Promenade and Nicoll Highway stations had been designed as a paired interchange, not unlike City Hall and Raffles Place, between what was then known as the Marina Line and a future, unknown MRT line. However, with the Nicoll Highway collapse, the old station site could no longer be used, and a new site had to be found. To speed reconstruction, the original station design was drastically simplified, losing the extra platforms for the future line in the process.
This left Promenade Station without a “partner”. Also, using the existing trackways for the planned future line would also have been problematic — it directly heads into the Circle Line tracks towards Esplanade station. While it had seemed a good idea at first, Singapore’s population growth caught the planners completely unaware, and with the service frequency expected to increase drastically, it didn’t seem so workable now.
New plans had to be drawn up. Fortunately, there was a Plan B: the Downtown Extension of the Circle Line, which we now know as Downtown Line Stage 1, and a proposed Circle Line branch to Marina Bay.
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Bayfront Station of the Downtown Extension, which then was still under planning, was thus redesigned so that it could become the new “partner” interchange, in place of Nicoll Highway station. But the Downtown Extension would only use 2 platforms of this new Bayfront station, continuing towards Chinatown (yes, imagine CCL trains running off to Chinatown!). This was perfectly fine as at that point, the Downtown Extension would use the Circle Line platforms of Promenade station, being part of the Circle Line.
A stub had also been left for a future connection towards HarbourFront station, the opposite terminus of the Circle Line, in order to make it a full circle. This would give the Circle Line three branches in the downtown area — to Dhoby Ghaut, to Chinatown, and towards HarbourFront.
This was also perceived as uneconomical, and later, it was decided to connect Bugis, the terminal of what would be the Bukit Timah line, to the spare platforms at Bayfront station and then on to Chinatown. A section of the Eastern Region Line would also connect to Chinatown, creating the Downtown line project as we know it today, and the unique situation at Rochor.
As the connection would pass the site of Promenade Station, they decided to put platforms there to provide a connection between the Downtown line and the Circle Line to Dhoby Ghaut, with the only possible site being a small sliver of land between the existing station and Millenia Walk. It was not possible to build a normal platform with trains running on both sides in that small area, and hence, the platforms were built stacked, with the lower platform reaching a depth of 34m (edit: can’t remember the exact number, but it’s not 43!) below ground.
When the Circle Line plan was drawn up (stitching together a few orbital LRT lines), there came an idea to connect HarbourFront and Bayfront stations through the port area, which would be redeveloped as a new waterfront downtown district. This was planned to happen only after 2030, though.
However, with the splitting off of the Downtown Extension into its own line, and that the Bukit Timah Line (and its depot) would not open until 2015, a place was thus needed to do maintenance of rolling stock without going all the way to SMRT’s Kim Chuan Depot and tying up said depot’s facilities. Hence, a small workshop was built near the NSL Marina Bay Station, with access from the stubs of the Circle Line section of Bayfront station. The opportunity was also taken to extend the Circle Line itself to Marina Bay, providing a second interchange downtown with the NSL and the future Thomson Line. If you look around Marina Bay station, you just might be able to find said mini-workshop.
A section of tunnel between Esplanade/Bayfront and Promenade was also modified to allow for the future construction of a tunnel between the two stations. The Downtown Line’s tunnels must pass under this two-level future junction as well.
Well, it seems that I’ve been talking more about the Circle Line’s history in this post, but to understand the positional constraints of the DTL, we need to understand how we even got here in the first place.