Little Things That Matter: Circulation at Transfer Stations

I’ve written before about some problems of metro network design in large cities. In brief, it’s important to maximize network effects in a multi-line system, which means offering plenty of transfers between lines. The perfect network should have every pair of lines intersecting in the center with a transfer, with possible additional intersections outside the center, again with transfers. In practice, it never works quite this way. There are always compromises, based on particular historical and geographical details of city layout. But probably the single biggest contributor to the issue is transfer capacity. This issue also has independent interest, but the two worst examples I know of involve the central transfer points of London and Paris, where many lines converge.

For a start, it’s worth asking why even have multiple stations. Why not just build a perfect star-shaped system? Two-line subway networks usually just cross once in city center. Three-line networks can intersect at one point (as in Stockholm and the first three lines of Moscow), but more commonly they intersect in a triangle of three city center stations. Central transfer points go way beyond three lines, though: Otemachi has five subway lines; Tokyo Station has a subway line and six independent JR East commuter lines; Chatelet-Les Halles has five Metro lines and two and a half RER lines; Bank and Monument together have four Underground lines and the Docklands Light Railway; Times Square has five subway lines, three of which are four-track. Why not just add more lines to the same central station? There are three distinct answers.

Coverage

Transit networks aren’t just about connecting large neighborhoods (“Upper West Side”) to a nebulously defined city center. They’re about specific connections. City centers are larger than a single subway stop, and much larger than a single subway stop in any city that has any business building four or more subway lines. In Stockholm, where three lines is about right, the CBD extends about two stops heading north and east of T-Centralen. New York, Paris, Tokyo, and London all have CBDs several square kilometers in area, so it makes sense to route lines in such a way that it’s easy to reach many points within the CBD from all directions.

Concretely, take Times Square and Grand Central. It’s useful to serve both of them on multiple subway lines, but a north-south line can only serve one. Thus, the 4/5/6 serve Grand Central, and the A/C/E, 1/2/3, and N/Q/R/W serve Times Square. The same process repeats itself at a number of nodes within Midtown, and within CBDs of other large cities.

Construction difficulties

Independently of the value of having extensive service in multiple directions from multiple points in the CBD, there is the cost of bringing lines together. In large cities, the biggest source of missed connections to begin with is that the street available for line 6 may happen to pass right between two widely-spaced stops on line 1, which never had a stop at this street because line 6 was not in the planning stages yet.

For the same reason, urban street networks make it difficult to serve one point from more than a few directions. Even lines bored deep under the surface, without regard for the street network, would find it difficult to go on level -9, beneath eight older lines. The stations with the largest number of independent lines all have tricks to make this work. Times Square has three north-south subways that don’t physically intersect (the 1/2/3 is always to the west of the N/Q/R/W and the A/C/E well to the west of both), a stub-ending east-west subway (the shuttle), and one deep-bored east-west subway (the 7). At Tokyo Station four of the six commuter lines are elevated at the same level. At Otemachi the lines form a square, with one side consisting of two lines that were built together at the same time. Chatelet-Les Halles has platforms that do not intersect, and the most difficult retrofit, the addition of the RER, was a massive excavation project that cost billions of euros.

The same construction difficulties are also relevant to small transfer stations. In Paris, transfer stations try to avoid superimposing one line’s platforms on top of the other, just because it’s hard to build. As a result, transfers often involve long walks; transfers at Chatelet are particularly labyrinthine.

Transfer capacity

The biggest problem is not coverage, and only partly related to construction difficulties. At the busiest stations, pedestrian circulation between platforms can be a challenge. London Reconnections has a fourpart series about Bank, where three deep-level Underground lines meet, all having built in the late 1890s, when expected ridership was far lower than it is today. Circulation is so obstructed that at rush hour TfL occasionally has to close the station for safety reasons, or else passengers would fall onto the tracks. Retrofitting the station with additional connections between lines as well as from the platforms to the street has been a daunting task, since the most logical places for escalators to one line would often pass through the platforms of another.

At Chatelet-Les Halles, the same problem occurs, if not so acutely that trains need to skip the station at rush hour. The passageways between the Metro platforms and between the Metro and the RER are long and narrow, and barely adequate to handle the large volume of passengers.

The simplest way to prevent this problem from occurring at a particular station is to make sure to design enough room for the transfer. The simplest way to do that, in turn, is to ensure transfers are cross-platform. The RER has such cross-platform transfers at the station, pairing westbound RER A trains with northbound RER B trains and eastbound RER A trains with southbound RER B trains. But even the wrong-way RER A-B transfers and the transfers involving the RER D are fine: the station’s extreme cost paid for a full-length, full-width mezzanine. The London Underground, too, retrofitted these onto some older lines when it built the Victoria line, which has cross-platform transfers at such key stations as Oxford Circus (the busiest in London not counting mainline stations – Bank is only the second busiest) and Euston.

However, cross-platform transfers connect two lines. I know of one place where they connect three: Jamaica Station, where one track in each direction has platforms on both sides, and passengers on the trains on the opposite sides of these platforms are sometimes told to walk through the train to transfer. This is a unique feature of regional rail, with its timed connections; subways with a train every 2-3 minutes can’t realistically time the connections, and without timing the connections, passengers are better off walking up and down to the other platform than waiting for a train to come in for a purely horizontal transfer.

The need for coordinated planning

The ultimate problem with using more cross-platform transfers if that they require a great deal of foresight. Retrofitting them is not always possible, and costs money in modification of existing stations. Hong Kong, Singapore, and Taipei all use these transfers extensively, but only on lines that were planned together, such as the first two lines in Singapore; Singapore’s newer lines have long (though spacious) transfer corridors, and Hong Kong’s lines inherited from the original MTR and from mainline rail have poor transfers.

With relatively limited opportunities to have high-capacity, high-quality transfers, it’s no wonder that most cities that build rapid transit try to avoid four- and five-way transfers when possible. Complex transfers like this can arise by accident, over several layers of planning – in the case of Paris, Line 11 was planned and built a generation later than Lines 1, 4, and 7; the RER was built a generation later than Line 1; and Line 14 was built a generation later than the RER, and indeed was designed as a relief line to the RER A.

Ultimately, the best way to prevent a situation like Chatelet or Bank from occurring is to know in advance where every line will go. However, this is necessarily a hard task. In the 1890s, London was a city of 6 million, with a large number of poor people living in overcrowded condition in East and South London; a planner could guess how the city would grow and suburbanize in the 20th century but would not be able to predict this with any certainty. Paris, the capital of a then-poorer and far less industrialized country, has grown even more tremendously – in 1901 Ile-de-France had 4.7 million people, not all living in the built-up area of the capital.

In very large third-world cities, the task of predicting future growth is somewhat easier, but only because they’re already very large and have informal transit pointing the way to the major corridors. I can draw a semi-serious Lagos metro proposal based on the city’s urban layout today and expect much of its future growth to come from increasing building heights so that the same density can be accommodated with less overcrowding, but I can’t meaningfully say which future areas will become hotspots that must be served from all directions or how far the suburban sprawl will go.

34 comments

  1. Bjorn

    A peculiar problem in some cities is connections between elevated and underground lines. Chicago has built a narrow-but-workable series of escalator switchbacks at Clark/Lake in the limited space they had between the Loop Elevated and the Blue Line.
    On the other end of the Loop Elevated, the connection between Harold Washington Library-State/Van Buren and the Jackson Street platforms of the Red and Blue lines requires passengers to make an out-of-system transfer. There doesn’t appear to be any obvious, aesthetically acceptable way to connect the two station complexes. (A pedestrian tunnel might be viable between Van Buren Street and the existing concourse under Jackson, but the concourse isn’t ADA accessible today and vertical access would need to be constructed between the new tunnel and the Harold Washington Library-State/Van Buren platforms.)

    • Eric

      Many newer systems avoid this problem by making all lines underground in the city center (where the transfers are), even if they are above ground in the suburbs (covering most of the route length).

      • Alon Levy

        Not just newer systems! Els on dedicated urban rail (as opposed to legacy commuter rail) are pretty rare. The dedicated Underground lines in London (i.e. not commuter branches later connected to the system) are underground or in railroad rights-of-way. Very little of the Metro here is elevated. In New York there’s the subway and there used to be the el, and the elevated parts are almost all pretty far out.

  2. Eric

    Multiple transfers at a single station also multiplies the number of passengers getting on/off at that station. This adds to dwell time and limits the line frequency.

    • Alon Levy

      Yeah, probably. Then again, London manages 35 tph on the Central line, and apparently plans 32 on the Bank branch of the Northern line once the Battersea extension opens.

  3. Eric

    3-way cross-platform transfers is not THAT difficult, although it is necessarily incomplete.

    A 2-way cross-platform transfer looks as follows:
    TpTTpT
    where T=track, p=platform, the left two tracks go one direction, the other two tracks go the other direction.

    Similarly, a 3-way transfer could look as follows:
    TpTpTTpTpT
    Of the three lines 1,2,3 there are cross-platform transfers 1-2 and 2-3. Ideally the busiest line should be 2.

    • adirondacker12800

      The train on track 2 loiters a bit passengers can transfer between 1 and 3 using 2 to cross between the two island platforms.
      But that’s the way the Long Island Railroad has been doing it for over century so there must be something inherently evil about it because as every body knows the LIRR can’t do anything right. If it’s really busy slap another island between the three track extravaganza and that single island can go in the peak direction.

      https://en.wikipedia.org/wiki/Jamaica_station#Station_layout

      Click on “show” to expand the diagram.

      • Alon Levy

        None of these trains is especially frequent at the peak… they run every, what, 7-8 minutes each? It works when you’re funneling eight tracks to four (ignoring the Atlantic Branch since it’s less busy) but not when you’re in the middle of a two- or four-track trunk.

      • Anton Willy Dubrau

        Many third rail systems can not have platforms on both sides, because third rail and platforms are not allowed to be on the same side. If you build a new system, it’s probably best to use overhead power anyway. So not a giant issue in general, but something to keep in mind.

        • Diego Beghin

          Really? Is this a regulatory issue in some countries? Rio and Brussels have 3rd-rail metros with some stations with platforms on both sides…

        • anonymouse

          That’s not an issue in literally any system that I know of. While all systems have a preferred side for the third rail (in Russia it tends to be tucked under the platform!) that doesn’t stop them from building platforms on both sides if they really have to. Can you think of an example of a system that entirely prohibits tracks between two platforms?

          • Martin

            Well, if someone falls in, they’ll most likely try to run back and climb up from the platform they fell from. I can see this being an issue. Maybe underrunning 3rd rail can help? Or platform screen doors just on that side?

      • Eric

        The problem with train 2 loitering is that it significantly slows down train 2. Also, if train 2 is busy (which it will be at rush hour), it will be difficult or impossible to cross 2 to get from 1 to 3.

        For this reason, I would tell passengers to transfer from 1 to 3 via the mezzanine. Except maybe disabled ones.

        • Max Wyss

          It may not be that critical if train 2 is some kind of shuttle without a tight schedule, so that it can enter first, and leave last. Or, if it changes direction, the extended stop is justified, and made use of. Note, as far as I can remember neither is the case in Jamaica, however.

  4. Eric

    An interesting cross-platform transfer variation is sometimes used in East Asia, where there are two consecutive transfer stations, each one cross-transfer for a different transfer. So, assuming a N/S line and an E/W line, one station looks as follows:
    NpEWpS
    while the next station is:
    NpWEpS
    so you can transfer cross-platform in either direction, you just have to wait a stop.

      • Eric

        Not exactly – here is the track map, there is only one 4-track station in Oakland.

    • Max Wyss

      In a high density network, this would require a flyover between the stations. Not cheap, but indeed feasible.

      • Eric

        Not cheap, but I’d say worth it in a place like Hong Kong (where the green line has 2 of these). I think Wuhan does too, possibly a couple other Chinese cities, I assume they are future-proofing for expected growth. Not sure about Japan or Korea or Singapore.

        • Alon Levy

          Singapore does this at Raffles Place and City Hall. At Raffles Place you can transfer cross-platform in the same direction (EB/NB, WB/SB), at City Hall one stop to the east/north you can transfer cross-platform in the opposite direction (WB/NB, EB/SB). It’s only two stations and not three because the North-South Line has just two (traditionally one) stops south of the interchange, so west-to-south and south-to-west transfers are less of a priority.

          I don’t think anywhere in Tokyo does that, at least not on the subway. In Tokyo everything happens in the context of very high land costs, so lines tend to follow streets and have poor transfers (often nonexistent).

          • Nicolas Centa

            Wikipedia says the only partial example in Japan is in the Chuo-Sobu local service and the Yamanote line, both surface trains operated by JR East.

            You can change North-West and South-East in Shinjuku and South-West in Yoyogi which is 1 station apart – but North-East is not possible.

          • Diego Beghin

            At Raffles Place you can transfer cross-platform in the same direction (EB/NB, WB/SB), at City Hall one stop to the east/north you can transfer cross-platform in the opposite direction (WB/NB, EB/SB)

            It seems like all possible transfers can be made cross-platform, why would you need a third station?

          • Alon Levy

            Because you need to travel an extra station in each direction to transfer cross-platform between Marina Bay and the western half of the East-West Line.

  5. po8crg

    I can think of one other place where there are transfers done through a vehicle, which is the tram (not train) stop at Victoria station in Manchester. This has three tracks with two platforms (described as four platforms in British English because we count platform faces not physical platforms). The centre track, while it is physically a through-track, is operated as a terminus for the airport line, which is run so that a tram waits in the platform until the next tram arrives. That way there is always a tram in the platform except when one is departing or arriving. Because there is always a tram in the centre platform, it’s easy for passengers to transfer across from one outer platform to the other. There is a route (level with the tracks) at the end of the platforms in case there isn’t a tram in the platform, but it doesn’t get used much except when there is disruption to services (when the centre platform gets used bi-directionally to increase the capacity of the station).

    Layout is TABTCDT (where T is a track and the other letters are the platform designations), so you can disembark at platform A, cross through the tram on BC and then board another tram at D.

  6. Telso

    Barking also has a cross-platform transfer through another train in limited circumstances. Looking at the station layout (bottom of PDF-pg. 34/35**), eastbound District line trains to Upminster have platforms on both sides (2 (which is really 2/3/4) and 1a (which is really 1/1a)) and generally open both doors. This allows passengers from Overground service to/from Gospel Oak on stub-end platform 1 (1/1a) to walk through the District line train to get to platforms 3 and 4 (2/3/4), which serve the stub-end of the Hammersmith & City line and the eastbound c2c service to Shoeburyness and Southend, respectively. (A photo.) This serves four separate services, three of which are thought of as urban(ish) rail services. This works reasonably well since the District line is typically 12 tph while the other services are 4 tph and 4/2 tph respectively, so a District line train is likely to come before another train, and because passenger volumes are low, so this won’t cause an unreasonable dwell time on the District line.

    However, there are a few issues. Often Hammersmith & City lines arrive on platform 2 (and also open both doors) and go to the sidings, and then return on platform 6. As well, some Overground service runs to platform 7, and with the Barking Riverside expansion of the Overground these trains will have to run to platforms 7 and 8 to use the c2c tracks towards Tilbury (station track diagram). Since the planned Overground frequency to Riverside is the same 4 tph, one can expect most or all Overground services to no longer serve platform 1, eliminating this transfer upon opening, est. 2021.

    As well, from the mezzanine (and Jubilee/DLR, after changing levels) in Stratford it may sometimes be more convenient to walk through a westbound Central line train from platform 3a to 3 to get to Shenfield metro services on 5 (with 3/5 the same platform). (Another photo.)

    Lastly, Hoyt-Schermerhorn may have used this way when the Court St shuttle was running.

    **pg 35 is a clearer schematic but 34 is to scale, though has an error, with District line service on track 6 being inbound to London.

    • adirondacker12800

      Lastly, Hoyt-Schermerhorn may have used this way when the Court St shuttle was running.

      They may have taken switches out. Putting the shuttle to Court Street on the Spanish Solution track would be a switching horror. Running a Fulton Street local through Court Street to Second Avenue would make a lot of sense.

      • Telso

        No, not using the shuttle as the middle train (what a mess for the interlocking!), using the A/C line as it is today. Get off the Brooklyn-bound G, walk through the Manhattan-bound A/C, get to the shuttle. Alternatively, get off shuttle, walk through the Brooklyn/Queens-bound A/C and get on the Queens-bound G. You can’t really do both directions unless you want people guessing which platform the shuttle will be on or you are okay making a mess of the other interlocking with non-revenue movements. But for the handful of people that didn’t want to just use Bergen Street or Jay Street-Metrotech, it could have been marginally useful for those 10 years. I could imagine it being neat to do on some museum tourist train run.

        • adirondacker12800

          If they were opening doors on both sides with one conductor, it loiters a bit. They may not have and passengers for Court Street had to go up and down. Apparently the Central Park West expresses, at Columbus Circle, back in the day, opened the doors to the central island first, for passengers exiting to the street and the IRT, then opened the doors on the other side. Even if it’s “fast” it will increase dwell time.

  7. Bgriff

    It is no longer active, but Hoyt-Schermerhorn has the same layout as Jamaica Station, though I have no idea if / how often anyone actually walked through a Fulton St. Express train to transfer between trains on the outer tracks back when all 6 were in service. And I suppose South 4th St was planned to do the same thing.

  8. Tonami

    MARTA in Atlanta has 2 levels of Spanish solution platforms at 5 points station. The intersection of the East – West (blue & green lines) and North – South ( Red and Gold lines). People regular use the middle train to cross to the other platform. I’ve watched people wait minutes for a train to come so they can walk right through rather than taken the escalators up and back down(this would be faster, crossing the train is more fun).

  9. FDW

    I’ve been working on this map for some time now. It’s still not finished, but since I don’t know when I’ll get the chance to work on it again (due to RL circumstances), I’m just going to drop it now:

    https://drive.google.com/open?id=1TPeAOOydLn7dvEfRYjAjVh6RSQM&usp=sharing

    This is the Seattle Metro concept that I’ve mentioned here. It’s a 7 (soon to be 9) line system. Trains are 160m long, 3.4m wide, use 1500V DC Overhead wire, and have a top speed of 110 kph. There’s also the Streetcar network (inherited from the original system), and a Regional Rail system (RER) that I plan reorganizing when I get the time. There was also a huge bus network that I wanted to add, but I haven’t had time for that.

    To be relevant to the topic at hand, the Metro system that I developed isn’t all that unusual for the version of America that it takes place in (Given how this Seattle has about twice the population of the Seattle in our world). But what makes Seattle stand apart is it’s tortured geography. This forces a whole lot of Elevated in the core, and an almost unheard of number of Elevated to Subway transfers. But station geometry is generally good, and transfers from Metro RER/Streetcar/Bus/Ferry are generally quick and easy.

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