Do you need double decker trains?
I am tired of hearing this argument, so it’s time to debunk it once and for all.
Certain folks always like to say that yes, double decker trains would be useful on the Singapore MRT.
I disagree. Firstly, there isn’t the space, and secondly, there isn’t the use. Let’s see how.
Tunnel vision
Let us first start with the anatomy of a tunnel. From this paper, the internal diameter of a tunnel is 5.8 metres as on the Downtown Line. However, to provide a steady, flat floor in the cylindrical tunnel, something known by LTA as “first stage concrete” is laid in the tunnel, on which the track is built on, which reduces the vertical space that is provided for the train itself.
Secondly, safety rules require that a walkway be provided at the side of the tunnel for the off chance where a train must be evacuated through the side doors, hence why the “door opening handles” on automated lines’ trains exist. It may be necessary to thus adjust the track itself off-centre to allow the walkway to fit into the tunnel. And after leaving space for the necessary cables and pipes for the railway systems, really, how much space is left?
So in summary, this is a very oversimplified view of what our tunnel looks like:
Leaving some more allowance for train movement and sway (physics/civil engineering heads call this the kinetic envelope), as well as tunnel movement over time due to ground conditions, we are left with space for a train that’s 3.2m wide and 3.7m high.
That is… actually not a lot, compared to contemporary double decker trains like the Sydney Trains A/B sets and the RER A trains (4.4m high). The slightly shorter Japanese commuter trains, with double deck Green (first class) cars and MRT-style second class cars, are 4m high. For comparison, a double decker bus is also typically about 4m high.
But why?
To be very fair, unlike the kind of medium-long commuter rail distances that you’d see double decker trains on, the average trip on the MRT also does not warrant having double decker trains as well. For that kind of distances, when you talk long distance or express buses like 161/168, 67 and 966, then perhaps the increased seating capacity provided by double deckers make sense.
But this is the MRT. Somewhat frequent stops at which have many passengers getting on and off. This means that it would be better to have more doors on our 22.8m long cars (like the TEL, which will have five) to facilitate quicker exchange. Since our MRT trains have high platforms, there will have to be staircase space needed within the vehicle to get to the lower and upper decks of a theoretical double decker vehicle — of which there won’t be space if you want to add doors. Something’s got to go — like the Sydney Trains vehicles with 2 doors, or the RER A ones with three doors.
We can further underline this with the Cross Island Line taking a bulk of the cross island traffic (call a spade a spade, right?). Given expected travel times and patterns on the Cross Island Line, there may be a case for having longitudinal seating on CRL trains, like the JR West 223 series. On the other hand, the relatively long distance E231 trains have mainly longitudinal metro-style seating in the commuter vehicles.
If post-2040 you still expect to be spending 45 minutes on a single train, then perhaps we can discuss that in the comments.
