I wrote a detailed proposal about why New York should deinterline, and how. I got a lot of supportive comments (in the transit blogging sense, i.e. nitpicking), but also some pushback, arguing that people like their one-seat rides, and making them transfer under a more coherent system would make their riding experience worse. I could go on about how London is facing the same problem and is choosing to invest a lot of money into deinterlining in order to increase train capacity, but in the case of New York, there’s a blunter answer: what one-seat ride? The extent of reverse-branching on the subway does not really give people one-seat rides, and New York City Transit is making service decisions that do not maximize one-seat rides even when doing so would be relatively painless.
Most outer branches with just one route naturally offer direct service to the route’s trunk line. Let’s look at the current subway_map, and compare it with my proposed deinterlining, which is again this:
Today, riders on the West End Line only have service on the D, so they only have a one-seat ride to Sixth Avenue. Riders on the Sea Beach Line only have the N, and riders on the local Brighton Line trains only have the Q, so they only have one-seat rides to the Broadway express trains, and if they want to travel to Prince Street or 8th Street-NYU on the R they have to change trains at Canal, which is not a cross-platform transfer. Only a handful of stations get genuine choice between the two trunk lines: 36th Street on the D and N, and the inner few express stops on the B and Q, say up to Newkirk Avenue. These are express stops, with more ridership than the locals, but they’re not the majority of ridership on the subway in Southern Brooklyn. The majority of riders have to deal with the drawbacks of both reverse-branching (slow, infrequent trains) and coherent service (fewer one-seat rides).
Queens Boulevard has the same situation: local and express patterns mix up in a way that makes the choice of one-seat rides much weaker than it appears on the map. Riders at the local stations can choose between the M and the R, two trains that are never more than a few blocks apart in Midtown; only one station on either line is inconvenient to access from the other, 57th Street/7th Avenue, the least busy stop on the Broadway Line in Midtown on a passengers per platform basis (49th and 5th have less ridership but have two platform tracks and no Q service). The express stops get more serious choice, between the E and F, but those are just three stations: Jackson Heights-Roosevelt Avenue, Forest Hills-71st Avenue, and Kew Gardens-Union Turnpike. Queens Plaza has E, M, and R service, but passengers actually getting on at Queens Plaza can equally get on at Queensboro Plaza and ride the N, W, or 7.
Genuine choice between two relatively widely-separated trunk lines on the same trunk only exists in two and a half places in New York: the Central Park West Line offers a choice between the B and C trains, the Nostrand Avenue Line offers a choice between the 2 and 5 trains, and the inner half of the White Plains Line offers a choice between the 2 and 5 trains off-peak (at the peak the 5 runs express, so local stations only get the 2).
New York is blessed with cross-platform interchanges, usually between local and express trains on the same line. Riders on the 1 train are used to transferring to the 2 and 3 trains cross-platform at 96th Street; in the morning, the 1 train’s busiest point is actually from 103th Street to 96th, and not heading into Midtown. With 170,000 boardings at its stations north of 96th per weekday, the 1 is much busier than Nostrand (with 60,000 weekday boardings) or the combined total of local Central Park West stations from 72nd to 116th (with 65,000 boardings). It’s also slightly busier than the White Plains Road Line, let alone the inner segment with both 2 and 5 service (which has 95,000 boardings).
In Queens, a similar situation occurs on the 7. The stations east of Queensboro Plaza, excluding 74th Street-Broadway (where the transfer to the Queens Boulevard Line is), have a total of 215,000 weekday boardings. The trains fill at the outer end and then discharge at 74th Street as most passengers transfer, not cross-platform, to the faster Queens Boulevard Line; then they fill again at the stations to the west and discharge at Queensboro Plaza, which has a cross-platform transfer to the N and W.
This is relevant to some of the few segments of the subway where reverse-branching offers choice between different trunk lines. Passengers on the Nostrand Avenue Line could transfer cross-platform at Franklin Avenue, where the platforms aren’t much narrower than at 96th Street and Broadway, where passenger volumes are almost three times as high. Similarly, passengers on the Central Park West Line and its branches to Washington Heights and Grand Concourse could transfer cross-platform at 125th Street or at Columbus Circle; Columbus Circle is extremely busy already with origin-and-destination traffic, and the interchanges between local and express passengers could not possibly overwhelm it.
Only one place has a difficult connection: 149th Street-Grand Concourse, the interchange between the 2, 4, and 5 trains. This also happens to be the most difficult deinterlining project in general, because of the merger of the 2 and 3 further south; it requires either closing the northernmost two stations on the 3, or opening up a few blocks of Lenox Avenue to construct a pocket track. Because of the disruption involved, this project can be left for last, and come equipped with more passageways at 149th Street, just as London is first deinterlining the Northern line to the south (raising peak capacity on the Bank branch from 26 trains per hour to 32) and leaving the north for later (which would raise capacity further to 36 tph).
NYCT has deinterlined in the past
Upper Manhattan witnessed two deinterlinings in the second half of the 20th century, one in the 1950s and another in the 1990s. The service NYCT inherited from its three predecessor networks had systematic route nomenclature taking into account conventional and reverse branching.
On the IRT, West Side trains were numbered 1 (to Van Cortlandt Park), 2 (to the White Plains Road Line), and 3 (to Harlem-148th Street), and Lexington trains were numbered 4 (to the Jerome Avenue Line), 5 (to the White Plains Road Line), and 6 (to the Pelham Line); 2, 4, and 5 trains ran express, 3 and 6 trains ran local, and 1 trains could be either local or express. In the 1950s, NYCT changed this system on the West Side so that all 1 trains became local and all 3 trains became express. This was the result of track layout: the junction at 96th Street is flat if 3 trains have to cross over to the local tracks and 1 trains have to cross over to the express tracks, but under today’s present service pattern there are no at-grade conflicts. NYCT chose capacity and reliability over offering one-seat rides from West Harlem and Washington Heights to the express tracks.
On the IND, trains were identified by letters. A, C, and E trains ran on Eighth Avenue and B, D, and F trains on Sixth Avenue; A and B trains went to Washington Heights, C and D trains to Grand Concourse, and E and F trains to the Queens Boulevard Line. Local and express trains were identified using letter doubling: a single letter denoted an express train, a doubled one (e.g. AA) a local. The single vs. double letter system ended up discontinued as few trains consistently run express (just the A and D) and several run a combination of local and express (the B, E, F, N, and Q), and NYCT slowly consolidated the trains on Eighth and Sixth Avenue until there were only seven services between them. Eventually the B and C switched northern terminals, so that now the C runs as the local version of the A and the B as something like the local version of the D. Passengers in Washington Heights who wish to use Sixth Avenue Line have to transfer.
The situation on the IND wasn’t as clean as the deinterlining on the IRT. But it shows two important things. First, changes in train service have made the original reverse-branching less tenable from an operational perspective. And second, the value of a one-seat ride from Washington Heights or Central Harlem to local tracks is limited, since everyone takes the express train and transfers at Columbus Circle.