From the Red Line
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From the Red Line

What about a Skytrain to T4?

It’s the holiday season and much of Changi Airport is back in business.

This didn’t come without drama, though. When the reopening of T4 was announced, even Jetstar was caught by surprise by the announcement; which said that they, too, would be required to move to T4. There was plenty of drama, but at least had a happy ending with Jetstar agreeing to move in March 2023. But why their initial reticence?

Here’s a bit of a thought experiment as to why, the main answer being around the lack of skytrain provision.

Beyond the obvious

Aviation blogs are quick to point out the usual tropes. “Far away!” “Must take a bus transfer!” “No MRT!” “Nasty thing just like the old Budget Terminal!” They’re not wrong, especially considering that gates G8-G19 of T4 use hardstands in the old Budget Terminal area. It also doesn’t help that the main body of T4 is even further away than the Budget Terminal was due to the size needed to build the facility.

I previously also mentioned an additional issue, with the Skytrain running at departure hall level and thus being unable to provide lengthwise transfers through the airport. With SIA moving back to T2 this makes things even more complicated than the previously scenario — a transit passenger from T2 to T1 D gates (or gates E20 to E28, which remained open) would have to take the long way around the airport, crossing both T1 and T3 main concourses on foot.

This is temporary while the rest of T2 remains under renovation, but I also can’t help but ask myself whether the need to cross main concourses on foot might be a ploy by CAG to expose more people to the duty free shops, compared to if they were to sail past above on elevated skytrain tracks. I must also at least point out that SIA has also minimized this need — most SQ-Scoot transfers are mostly from SQ transcontinental flights to Scoot regional services, and the transcontinental flights are handled at T3 already. There’s still a need to walk, but at least there’s one less skytrain ride. And perhaps Scoot may move back to T2 soon so that there’s no need to transfer across three main terminals.

Before 2020, the T4 shuttle bus in the transit area of the airport was boarded from Gate F51 — this means you need to cross the T2 concourse, and if coming from T1 C gates, you also need to cross the T1 concourse as well. At least now they’ve shifted it to T1 Gate C21, with the shuttle bus making an additional stop at T3 Arrival A before going to T4. Still, habits are going to be hard to break.

Plans are just paper

What if I told you that in the initial days, Changi Airport actually planned to build a skytrain line to “T4”? In a conference paper detailing the planning steps and early construction of the current skytrain system, the authors detailed:

Possible future expansions of the PMS include: a 2-station (Station F and a new station) single lane shuttle of about 500 m in length serving the southside of Terminal 2, and a 4-station dual lane shuttle of about 1400 m to serve a future Terminal 4.

The “Terminal 4” mentioned here does not appear to be Changi East, or what we now call Terminal 5, since it seems to be too near. I must thus assume that 1400m away from the nearest possible point on the Skytrain leads to the location of the current Terminal 4 — or at least, the South Remote Apron across Airport Boulevard from T4. It also doesn’t help that a curiously placed stub near the maintenance facility at the south end of T3 also provides a hint for a future expansion.

To somewhere. (source: Google Maps)

But this extension may have been very complex to build — at first. They are right when they say it’s too difficult to tunnel. You have to build a ramp, and don’t forget about having to go under the overpass that takes aircraft taxiways over Airport Boulevard. Then going too close to Airport Boulevard is probably out of the question as well, with all the feeder roads merging in and out to provide access to other airport facilities. But this might be a solvable problem, perhaps if they dare to build a high bridge to allow the skytrain to pass over the taxiways, as was done in Hong Kong.

The difference in security concepts might also have been another consideration. Since T4 has centralised security screening and T1–3 do not, it is thus necessary to conduct screening for passengers going to T4. With the shuttle bus system, this can be done at existing bus gates (and perhaps they may have another one at T3 Arrival A), but with a skytrain system, it may have been necessary to find ways to hook the skytrain station into T4’s arrival and departure flows.

And even if this was built, a more pertinent issue for Jetstar is the lack of a direct connection. They have a bus now from T1, where most of their interlining partners are. But with a skytrain, they would likely have had to make passengers first take a skytrain from T1 to T3, walk across the T3 main passenger concourse, then another skytrain from T3 to T4.


These issues may be more related than we think.

If you wanted to build a skybridge, it might not have been possible to connect from that stub near T3 without finding a way to gain significant height. Rubber tyred vehicles may be able to climb steeper slopes, but there’s only so much gradient you can put in before people start losing control of their luggage carts. Tracks might thus have to start at a higher level in order to build a bridge high enough for the largest planes to pass underneath, as Hong Kong, KLIA, London Gatwick, and Seattle did. This bridge will also need to be long enough to accommodate two parallel taxiways, which in itself may be a world-record feat.

Such a bridge will not be cheap, even if we’re carrying skytrains on the bridge instead of providing a fully-equipped walkway for passengers and can save weight on some of the mechanical systems needed for passenger comfort.

Likewise, instead of the usual Changi formula of expecting people to take a cab out of the airport, cheaper flights at T4 with all the budget airlines there appeal more to the value traveller, who may be more open to using public transport to get to the airport. We may see more of this especially with passengers avoiding cabs due to increased prices and potentially lower supply too.

As it stands, these passengers take a shuttle bus from T3, using that exit from the MRT. Alternatively, they can take a public bus, but the clockwise nature of public bus services means that they have to wait for the bus to call at all other terminals first, before going to T4. And not every bus calls there too — this situation could be fixed, but it might be additional resources for not a lot of benefit.

It might thus make sense for any potential skytrain station to close the gap nearer to the MRT, avoiding the need to cross the T2 or T3 main concourse on foot. You could thus take advantage of that need for height to build an extension over the main concourse between stations A-B or E-F, but that didn’t happen with the T2 upgrading and is unlikely to happen with T3 as well.


Based on previews, Terminal 5 is likely to introduce yet another separate skytrain system, this time potentially underground or at least at a lower level, in order to cross Runway 2. The level change might be unavoidable at least without some form of vehicle lift or other technology, but it means Changi will need to operate and maintain three skytrain systems. Depending on how the system is designed, it could be at least two changes of train to get from T1 or T3 to T5, similar to the current situation we have with T4.

That’s just a symptom of a greater issue, that is the presence of what will become three main precincts within the airport. While it is likely that Changi may eventually expand the current T4 bus transfer network to connect to T5 as well, and should the airport rehouse airlines according to airline grouping in the future, inter-precinct travel may not be so important, but it’s still important to do something about intra-precinct travel.

Some, like AirAsia, may be content to remain where they are, being able to keep their operations within a single precinct. In any case it appears that for now T4 appears to be relatively quiet (how often are the H bus gates used, anyway), so there may not be such a need. But should the airport need to expand through T4, it may find itself without much of a choice but to think about a skytrain link.

Perhaps even the four stations mentioned in the earlier planning proposal might happen, with some kind of satellite terminal built as well. But that said, all these may be well after completion of all phases of T5. And perhaps we can also hope somehow the HSR gets built, so flights to Malaysia are reduced and we don’t need that capacity.



Here to make you think about transport issues in the Garden City of Singapore. You can say that I love controversy. Posts can get technical! Abuse of comments may be blocked. Subscribe to Telegram for updates:

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