In my writings about metro network design I’ve emphasized the importance of making sure every pair of intersecting lines have a transfer. Moreover, I’ve argued that missed connections often come from having very wide stop spacing, because large metro networks have very closely-spaced lines in the core, and if the stop spacing in the core is too wide, as in Moscow, then lines will frequently cross without transfers. In contrast, in Paris, where the Metro has very closely-spaced stops, there is only one missed connection on the Metro, between Lines 5 and 14. However, what’s missing from this discussion is what to do on lines that, due to network design, have to run express and miss some connections. This question mattered to most RER lines and currently matters to Crossrail and Crossrail 2, and will be critical in any New York regional rail plan.
I claim that the most important connections to prioritize should be to,
- The busiest lines.
- Lines that are orthogonal to the newly-built express lines.
But before explaining this, I’d like to go over the scale of the underlying problem of prioritizing transfers. For a start, look at the Underground in Central London:
Crossrail is the dashed gray line. Between Paddington and Liverpool Street, it intersects seven north-south lines, including five in rapid succession on the West End; stopping at all of Bond Street, Oxford Circus, Tottenham Court Road, and Holborn would slow down too much what’s intended to be an express relief line to the Central line.
Stopping between two stations and having transfers to both is possible – look at Farringdon-Barbican and at Moorgate-Liverpool Street – but results in very long transfer times. The RER has opted for this solution at Auber, which is located between the Opera and Saint-Lazare, with a transfer stretching over three successive stations on Line 3, leading to legendarily labyrinthine transfers between the RER and the Metro:
Observe that in contrast with the RER A’s convoluted transfer at Auber, the RER B simply expresses between Chatelet-Les Halles and Gare du Nord, missing the connection to the east-west Lines 3, 8, and 9 and the north-south Line 7, and only connecting to the circumferential Line 2 via a long underground passageway. The reason for this is that a transfer station at Bonne Nouvelle or Sentier would be very expensive to construct; the RER’s stations were all extremely costly, and the RER A’s record of $750 million per km for the Nation-Auber segment remains unbroken outside the Anglosphere. On Crossrail (the recordholder in cost per km outside the US, soon to be overtaken by Crossrail 2), it’s the stations that drive up costs as well, and the same problem is even more acute in New York.
The tension is then between the network effects of including more transfer points, and the costs and slowdowns induced by stopping more often. The first point in my claim at the beginning of this post follows immediately: it’s more valuable to stop at transfer points to busier lines. The RER A misses Line 5 entirely, as does the express Line 14, because Line 5 is so weak that it’s not worth it to detour from Gare de Lyon through Bastille to connect to it; the oldest plans for the RER A had a stop at Bastille and not at Gare de Lyon, but under SNCF’s influence the system was redesigned to connect to the train stations better and thus Bastille was replaced.
Whereas the RER A in theory connects to every north-south one except the weakest (although the second strongest after Line 4, Line 13, has an even longer connection than at Chatelet), Crossrail does the opposite. The busiest station in London excluding mainline stations is Oxford Circus, thanks to the three-way transfer of the Bakerloo, Victoria, and Central lines; the Victoria line is the busiest in the system per km (although the longer Northern and Central lines have more riders), and it’s certainly the busiest north-south trunk line. However, plans to have a transfer to both Bond Street and Oxford Circus were rejected in favor of a connection to Bond Street alone. The reason is that London’s low-capacity passageways get congested, and TfL’s hamfisted solution is to omit critical transfers, a decision also made at the Battersea extension of the Northern line, which will miss a connection to the Victoria line at Vauxhall.
This brings me to the second transfer priority: it’s the most important to connect to orthogonal lines. The reason is that parallel lines, especially closely parallel lines, are less likely to generate transfers. New York’s four-track subway lines have very high volumes of local-express transfers, because those are easy cross-platform interchanges; as soon as any walking between platforms is required (for example, on the Lexington Avenue Line at 59th and 86th Streets), transfer volumes fall dramatically. In Paris, transfers between Line 1 and the RER A happen, but usually for longer-distance travel; I find it faster to take Line 1 from Nation to Chatelet than to take the RER A, even without any transfer, purely because it’s easier to get between the street and the Metro platforms at both ends.
This issue was never really in contention when Paris built the original RER system. The one place where the RER prioritized a transfer to a same-direction Metro line over an orthogonal one, Gare du Nord, is such an important destination for commuter and intercity trains that it’s obviously justified to prioritize it over an easier connection to Line 2. However, more recently, the RER E has seen this issue surface with the location of the infill Rosa Parks station. The RER E could have sited a station at the intersection with Line 5, but Line 5 goes northeast and serves much the same area as the RER E, so the network effects from an interchange would be weak. Instead, the station is sited to interchange with the circumferential T3 tramway, which opens up a connection toward Nation and eventually toward Porte d’Asnieres.
In London, the same question is critical to the central route of Crossrail 2. The current plan has three Central London stops: Victoria, Tottenham Court Road (with a transfer to Crossrail), and Euston-St. Pancras. But Victoria itself is not much of a destination, and of the two lines served, the District and the Victoria, the Victoria line is parallel to Crossrail 2 rather than orthogonal to it. The purpose of Crossrail 2 is to add north-south capacity through the West End to decongest the Victoria line and reduce the shuffle at Victoria station between mainline trains and the Underground; to this end, there’s no need to stop at Victoria station itself.
To this effect, Martha Dosztal proposes moving Crossrail 2 to Westminster or possibly Charing Cross. Instead of spending $2 billion on a station at Victoria, London would need to spend probably a comparable amount on a station that interchanges with lines that go northwest-southeast like Jubilee or Bakerloo rather than on the parallel Victoria line; moreover, Westminster and Charing Cross both have connections to the District line, so Crossrail 2 would still connect to all three east-west Underground lines.
Finally, the application to New York is the most delicate. New York’s scores of missed connections come from deliberate indifference on the IND’s part to transfers with the older lines rather than any systematic attempt at prioritizing important interchanges; the older IRT and BMT systems have between them just two missed connections (3/L in Brooklyn, 4-5/R-W in Lower Manhattan). But including better connections in the event the city builds more rail lines remains critical. Second Avenue Subway gets this right by having a cross-platform transfer to the east-west F; there’s no transfer to the north-south Lexington Line, but this is less important given Second Avenue’s role as a Lexington relief line.
Regional rail transfers are especially circumscribed in New York given the system’s nature as a few short tunnels: new tunnels across the Hudson, and ideally a connection between Penn Station and Grand Central. This is why there is little room for improving connectivity between the subway and what I call Lines 1-3 of New York regional rail. However, the priorities I’m advocating in this post suggest two important things about Penn Station: first, it’s important to reopen passageways to Sixth Avenue to allow connections to the NQRW and BDFM trains; and second, it’s not important to have a connection to the 7 at Hudson Yards, as IRUM proposes.
On more speculative lines involving longer tunnels, the same priorities point to my proposed stopping pattern in and around Lower Manhattan. What I call Line 4, a north-south line from Grand Central to Staten Island stopping at Union Square and Fulton Street would intersect the east-west subways: the 7 at Grand Central, the L at Union Square, and PATH and most Brooklyn-bound trains at Fulton Street. The only missed subways – the F/M at Houston Street and the N/Q at Canal – go mostly north-south (except the M, which has a same-platform transfer with the J/Z, connecting at Fulton). Likewise, what I call Line 5, connecting from Pavonia to Atlantic Terminal, would connect to most north-south subways at Fulton Street.
Ideally, it’s better to make every interchange, and subway builders around the world should aim for very long-term planning in order to prevent missed connections in the future. However, when the inevitable changes happen and missed connections are unavoidable, there are emergent rules for which are more important: busier lines are more important than less busy lines, and less obviously, lines that are orthogonal to the new line are more important than ones that are parallel. These priorities make it possible to build express lines that maximize regional connectivity with minimal loss of travel time due to making local stops.