Cross-Platform Transfers

I did a complex Patreon poll about series to write about. In the poll about options for transit network design the winning entry was difficult urban geography, covered here and here; the runner-up was cross-platform transfers.

Subway users have usually had the experience of connecting at a central station so labyrinthine they either were lost or had to walk long distances just to get to their onward train. Parisians know to avoid Chatelet and New Yorkers know to avoid Times Square. It’s not just an issue for big cities: every metro system I remember using with more than one line has such stations, such as T-Centralen in Stockholm, Waterfront in Vancouver, and Dhoby Ghaut in Singapore. To prevent such connections from deterring passengers, some cities have invested in cross-platform interchanges, which permit people to transfer with so little hassle that in some ridership models, such as New York’s, they are treated as zero-penalty, or equivalent to not having to transfer at all.

Unfortunately, improving the transfer experience is never as easy as decreeing that all interchanges be cross-platform. While these connections are always better for passengers than the alternative, they are not always feasible, and even when feasible, they are sometimes too expensive.

Cross-platform transfer to wherest?

Consider the following two-line subway interchange:

A cross-platform transfer involves constructing the station in the center so that the north-south and east-west lines have platforms stacked one on top of the other, with each east-west track facing a north-south track at the same platform. The problem: do eastbound trains pair up with northbound ones and westbound trains with southbound ones, or the other way around?

In some cases, there is an easy answer. If two rail lines heading in the same general direction happen to cross, then this provides a natural pairing. For example, the Atlantic Branch and Main Line of the LIRR meet at Jamaica Station, where the cross-platform transfer pairs westbound with westbound trains and eastbound with eastbound trains. In Vienna, this situation occurs where U4 and U6 intersect: there is a clear inbound direction on both lines and a clear outbound lines, so inbound pairs with inbound and outbound with outbound.

However, in most cases, the transfer is within city center, and there is no obvious pairing. In that case, there are two options.

Near-cross platform transfer

Some transfers are nearly cross-platform. That is to say, they have trains on two levels, with easy vertical circulation letting people connect between all four directions. In Berlin, there is such a transfer at Mehringdamm between U6 and U7 – and in the evening, when trains come every 10 minutes, they are scheduled to offer a four-way timed interchange, waiting for connecting passengers even across a level change.

Multi-station transfer complex

Singapore, Stockholm, and Hong Kong all offer cross-platform transfers in multiple directions by interweaving two lines for two or three consecutive stations. The three-station variant is as in the following diagram:

At the two outer transfer stations, the cross-platform connections are wrong-way relative to the shared trunk corridor: eastbound pairs with northbound, westbound pairs with southbound. At the middle station, connections are right-way: eastbound pairs with southbound, westbound pairs with northbound.

Of note, the shared trunk has four tracks and no track sharing between the two different subways. I’ve proposed this for the North-South Rail Link. The reason three stations are needed for this and not two is that with only two stations, passengers would have to backtrack in one pairing. Nonetheless, backtracking is common: Stockholm has three stations for the transfer between the Green and Red Lines but only the northern one is set up for wrong-way transfers, so passengers connecting wrong-way in the south have to backtrack, and Singapore has two stations between the East-West and North-South Lines, since one of the pairings, west-to-south, is uncommon as the North-South Line extends just one station south of the transfer.

Why are they not more widespread?

The inconvenience of Parisian transfers is a general fact, and not just at Chatelet. Two lines that meet usually meet at right angles, and the platforms form a right angle rather than a plus sign, so passengers have to be at one end of the train to have easy access to the connecting platforms. The reason for this is that Paris built the Metro cut-and-cover, and there was no space to reorient lines to have cross-platform transfers.

In contrast, both Stockholm and Singapore had more flexibility to work with. Singapore deep-bored the MRT for reasons of civil defense, contributing to its recent high construction costs; the tradeoff is that deep boring does permit more flexibility underneath narrow streets, which all streets are compared with the footprint of a cross-platform interchange. Stockholm used a mixture of construction methods, but the four-track trunk carrying the Green and Red Lines is above-ground in the Old City but was built with a sunk caisson at T-Centralen.

In London, similarly, there are cross-platform transfers, involving the Victoria line. It was built in the 1960s around older infrastructure, but at a few spots in Central London, the tubes were built close enough to old lines to permit cross-platform interchange in one direction (northbound-to-northbound, southbound-to-southbound). In contrast, the surface network, constrained by land availability, does not feature easy interchanges.

While deep boring makes cross-platform transfers easier, either can exist without the other. If I understand this correctly, U6 was built cut-and-cover. There were even weaves on the IND in New York, but they were expensive. Moreover, when two lines are built under a wide street with two branching streets, rather than on something like a grid (or even Paris’s street network, which is gridded at key places like where M4 runs under Sevastopol), cut-and-cover construction can produce a cross-platform transfer. Conversely, such transfers do not exist in all-bored Moscow and are rare in London.

The importance of planning coordination

Ultimately, cross-platform transfers boil down to coordinated planning. Some cities can’t build them even with coordination – Paris is a good example – but absent coordination, they will not appear no matter how good the geography is. Stockholm, Berlin, Vienna, Singapore, and Hong Kong are all examples of centrally planned metro networks, without the haphazard additions of New York (which was centrally planned on three separate occasions) or London (where the early lines were built privately).

Even with coordination, it is not guaranteed cross-platform transfers will appear, as in Moscow. Planners must know in advance which lines they will build, but they must also care enough about providing a convenient transfer experience. This was not obvious when Moscow began building its metro, and regrettably is still not obvious today, even though the benefits are considerable. But planners should have the foresight to design these transfers when possible in order to reduce passenger trip times; ultimately it is unlikely to cost more than providing the same improvements in trip times through faster trains.

27 comments

  1. marvin gruza

    While cross platform transfers are best, direct transfers where one has to travel just 1 straight flight of steps to be on the next platform works well. If done in more wide open stations where the high tracks cross the lower ones on what looks like a bridge if seems easier as well. It works especially well where one line has an island platform and the other has side platforms thus requiring but 2 sets of steps/escalators/elevators. The good and bad is that separate staircases are required for those transferring and for those entering and exiting the station.

    Very interesting is train to train transfers where 2 or 3 trains are close enough to each other to allow movement between without using a platform. This of course requires coordination of schedules and holding trains.

  2. threestationsquare

    Moscow has plenty of cross-platform transfers. Central examples include Kitay-Gorod on lines 6 & 7 and Tretyakovskaya on lines 7 & 8; outlying examples include Kashirskaya on lines 2 & 11A, Park Pobedy on lines 3 & 8A, Petrovsko-Razumovskaya on lines 9 & 10, and Dmitriya Donskogo/Starokacholovskaya on lines 9 & 12. All-bored St Petersburg also has an important central cross-platform transfer at Technologicheskiy Institut on lines 1 & 2.

  3. adirondacker12800

    New Yorkers know to avoid Times Square.

    Which is why no uses the shuttle. Rather silly of them to have three tracks of it, isn’t it?

  4. Jhonny

    What about transfers between different modes?

    In Nuremberg the two subway interchange stations actually in use (Plärrer and Hauptbahnhof) are doing okay given that they have to handle three lines.

    But try to change from U- to S-Bahn and you’re in for a world of hurt. Fürth Klinikum / Unterfarrnbach is probably the worst example, but the others are hardly better.

    Of course the lacking tram/subway connections may be due to the original plan to shut the tram down, but it’s still entirely too labyrinthine at many stations, particularly Nuremberg Hauptbahnhof.

    Now in Munich they have one station where S-Bahn and U-Bahn actually stop side by side cross platform… On the other hand, Munich main station is a mess and somebody calculated an eight minute transfer time for the new tunnel of the S-Bahn currently under construction.

    • ckrueger99

      In Philadelphia, we have transfers between trams (which run as locals below Market St between 30th and 15th Sts) and subway (express). But this can’t be cross platform, as the trams run on the outer tracks and the tram cars exit doors open to the right only. Which is a shame.

    • Matthew

      Amsterdam has cross platform transfers between metro trains and regional NS trains at Amstelstation.

      There is also another type of timed transfer there, the same platform local/express transfer. Get off the local train to Utrecht at Amstelstation, wait a moment on the platform and the express train to Utrecht picks you up from the same track and then goes nonstop to Utrecht, using passing tracks. Similarly going back to Amsterdam the express passes the local and drops you off before the slower train arrives. Repeat every ten minutes all day.

  5. Milan

    Mehringdamm doesn’t actually have trains on two levels; there is cross-platform interchange, but you do have to go via the mezzanine to interchange.
    Jungfernheide (now U7 only) was planned to have this, but the U5 extension was never actually intended to be built in less than 15 years.
    The stations in Steglitz that were to be shared between the U9 and U10 would have been built with U9 on the upper level and U10 on the lower level, but only the U9 has been built, running on the lower level only (to avoid the sidings being under the railway line for political reasons).
    Nollendorfplatz kind of has this, but I’m not sure about the exact layout.

  6. Alex Mazuretsky (@mazuretsky)

    Do the more complicated interchanges, these two and three station things actually make sense? Typical station spacing is around 800 metres. Three stations of parallel running track will be about 2.4 km. It may mean that you will not be able to fit more than one or two of these interchanges within the city centre (where most interchanges happen to take place). Additionally, it is 2.4 kilometres of both lines running not quite on the shortest path to the suburbs they serve. For systems with more frequent station spacing it may make a bit more sense, but there the additional cost of flyovers may be substantial, and flat junctions will be reducing capacity (although to be fair most of such systems have their fair share of street-running, traffic lights, sometimes sharing space with cars, and two flat junctions will be almost unnoticeable).

    • Alon Levy

      It’s 1.6 km, not 2.4… and evidently it works in Stockholm, which has a small city center (but benefits from having a sub-center in Slussen). In a city with a very large center like London or Paris, it shouldn’t be a huge deal. In fact there are a couple of places where two separate lines have two consecutive interchanges: Charing Cross and Embankment, Kings Cross-St. Pancras and Euston, Hotel de Ville and Chatelet, Republique and Arts et Metiers, Raspail and Denfert-Rochereau. Paris also has M8 and M9 running alongside each other for a couple stops, without cross-platform transfers. In New York there are a bunch of places with two consecutive express stations and one with three, 34th-42nd-50th on the B/D/F/M, and one place with sort of three consecutive transfers, Canal/Chambers/Fulton on the J/Z (the first two transfer to the 6, the last two to the 4/5).

  7. Alex Mazuretsky (@mazuretsky)

    Also, I would say that London’s largely privately-built rapid transit system had several examples of voluntary cooperation, joint ownership, and the government trying to overcome the coordination problems (surprisingly, this is how we ended up with Bank-Monument(-City) monstrosity, the Parliament imposed connections on the companies in question). However, even the lines built in deep bored tunnels mostly followed city streets for legal reasons. This means that there wasn’t much space for complex engineering underground.

  8. James Sinclair

    Metrocenetr in DC is a great transfer. Even though theyre on different levels, everything is wide open, so you immediately can tell what is going on.

    What makes a maze confusing is all the walls and blocked sightlines. You cant tell where you are compared to where you want to be.

    • Alex B.

      Metro in DC is an example where even with foresight, planning is still hard.

      All 3 of DC’s big interchanges involve lines crossing at right angles; it’s possible to envision alignments for the stations that could’ve produced cross-platform transfers, but that would’ve been a big change and involved a lot more construction on/under private property.

      That said, those transfers work OK. Gallery Place-Chinatown is the worst of the bunch because of the platform layout.

      The real missed opportunity in DC is at Rosslyn and Pentagon; these stacked platforms were built in such a way that it’s very hard to make them 4-track stations to support future expansion. Instead, they’ll have to build a whole new train room at Rosslyn with a ~450 foot walkway to transfer: https://ggwash.org/view/35293/a-wye-is-out-but-a-second-rosslyn-station-may-make-more-blue-line-trains-possible

  9. Bgriff

    Speaking of Singapore, I was recently there and I would love to read your thoughts on why and how there are such a massive number of missed connections on some of its newer lines, notably the Downtown Line with the older lines in the city center, as well as with itself when it loops around. The way the system is set up today, you would almost think it was like London or New York where the older lines (north-south/east-west) and the newer lines (downtown, circle) were each built by a separate operator and were coherent on their own, just not when switching between networks.

    Some trips are still possible to make in other logical ways, like spoke-to-spoke trips made via transfers outside the city center, but a lot of logical-seeming connections for shorter trips within and close to the city center aren’t possible (and given Singapore’s perpetual heat, it is understandable to want to use the trains even for shorter trips). Any idea what they were thinking?

    • Alon Levy

      I genuinely don’t know why there are so many missed connections. I can sort of explain why the Downtown Line self-intersects – it’s an amalgam of two different lines and the loop part of the self-intersection is where the CBD is – but I don’t know why it misses the other lines.

      • yuuka

        Of three, actually. I write about it here: https://medium.com/from-the-red-line/when-life-gives-you-lemons-7165015c153e

        In general, though, underground infill stations is something that has never been done in Singapore, owing to the conservatism of our planners (we had a pretty bad subway construction accident in 2004 that scared the living daylights out of them, google Nicoll Highway collapse). Platforms are always straight and level to provide accessibility to trains, avoiding situations where staff have to put up manual boarding ramps and such like you see in Japan. However, recent changes to the fare structure have made it possible to do a walking transfer between nearby stations using existing pedestrian infrastructure.

        As for the missed connections, I’ll go in order:
        – the North South Line passes just next to Downtown station, but there’s no platforms there. This is because Downtown station is already pretty close to Marina Bay station (1-2 train lengths), and an interlocking exists nearby on the NSL that would make it difficult to build platforms. Underground pathways exist to bring you to Raffles Place though.
        – the East West Line passes under the Downtown Line between Downtown and Telok Ayer, in a semi-stacked configuration as it prepares to enter the Raffles Place cross-platform interchange. See above.
        – Bencoolen station is right smack between Dhoby Ghaut and Bras Basah stations. There’s an interlocking on the Circle Line nearby, and Bras Basah is already within walking distance anyway, just pardon the depth. (something could be done at low levels though, but it would require land acquisition). As for the NSL, see above.
        – Rochor/Jalan Besar, where the DTL crosses over itself, is built under land earmarked for an expressway. I’m given to understand that it was cost/complexity issues that prevented an interchange being built.

    • Eric

      It seems to me that all the missed connections are on the Downtown Line between Downtown and Jalan Besar (a 6 station stretch with 1 made connection and ~3 missed connections). To be honest all 3 missed connections could be fixed with ~300m long underground pedestrian tunnels – if I were the planner, those would be a priority.

  10. London Tube User

    There is one example of a cut-and-cover cross-platform interchange in London. Mile End is an underground interchange between the (cut-and-cover) District Line and the (bored) Central Line. The entire station is on one level, with the Central Line rising up to cut-and-cover level to achieve cross-platform interchange. This is very much the exception, however, and it is worth remembering that Mile End’s Central Line platforms are between the above-ground Stratford and the deep-level Bethnal Green.

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    • fbfree

      It is interesting that Lionel-Groulx involves adding nearly 1 km of track for the green line to double back on itself for the cross platform transfer. Given that the track to Atwater was built and operating before Lionel-Groulx and the Verdun extension was built, I would have to look up whether this was an intentional design decision in the initial metro planning, or the result of changing plans.

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