Category: Urban Transit

Transit and Scale Variance Part 2: Soviet Triangles

Continuing with my series on scale-variance (see part 1), I want to talk about a feature of transit networks that only exists at a specific scale: the Soviet triangle. This is a way of building subway networks consisting of three lines, meeting in a triangle:

The features of the Soviet triangle are that there are three lines, all running roughly straight through city center, meeting at three distinct points forming a little downtown triangle, with no further meets between lines. This layout allows for interchanges between any pair of lines, without clogging one central transfer point, unlike on systems with three lines meeting at one central station (such as the Stockholm Metro).

The name Soviet comes from the fact that this form of network is common in Soviet and Soviet-influenced metro systems. Ironically, it is absent from the prototype of Soviet metro design, the Moscow Metro: the first three lines of the Moscow Metro all meet at one point (in addition to a transfer point one station away on Lines 1 and 3). But the first three lines of the Saint Petersburg Metro meet in a triangle, as do the first three lines of the Kiev Metro. The Prague Metro is a perfect Soviet triangle; Lines 2-4 in Budapest, designed in the communist era (Line 1 opened in 1896), meet in a triangle. The first three lines of the Shanghai Metro have the typology of a triangle, but the Line 2/3 interchange is well to the west of the center, and then Line 4 opened as a circle line sharing half its route with Line 3.

Examples outside the former communist bloc are rarer, but include the first three lines in Mexico City, and Lines 1-3 in Tehran (which were not the first three to open – Line 4 opened before Line 3). In many places subway lines meet an even number of times, rather than forming perfect diameters; this is especially bad in Spain and Japan, where subway lines have a tendency to miss connections, or to meet an even number of times, going for example northwest-center-southwest and northeast-center-southeast rather than simply crossing as northwest-southeast and northeast-southwest.

But this post is not purely about the Soviet triangle. It’s about how it fits into a specific scale of transit. Pure examples have to be big enough to have three subway lines, but they can’t be big enough to have many more. Moscow and Saint Petersburg have more radial lines (and Moscow’s Line 5 is a circle), but they have many missed connections, due to poor decisions about stop spacing. Mexico City is the largest subway network in the world in which every two intersecting lines have a transfer station, but most of its lines are not radial, instead connecting chords around city center.

Larger metro networks without missed connections are possible, but only with many three- and four-way transfers that create crowding in corridors between platforms; in Moscow, this crowding at the connection between the first three lines led to the construction of the Line 5 circle. In many cases, it’s also just difficult to find a good high-demand corridor that intersects older subway lines coherently and is easy to construct under so much older infrastructure.

The result is that the Soviet triangle is difficult to scale up from the size class of Prague or Budapest (not coincidentally, two of the world’s top cities in rail ridership per capita). It just gets too cumbersome for the largest cities; Paris has a mixture of radial and grid lines, and the Metro still undersupplies circumferential transportation to the point that a circumferential tramway that averages 18 km/h has the same ridership per km as the New York City Subway.

It’s also difficult to scale down, by adapting it to bus networks. I don’t know of any bus networks that look like this: a handful of radial lines meeting in the core, almost never at the same station, possibly with a circular line providing crosstown service. It doesn’t work like this, because a small-city bus network isn’t the same as a medium-size city subway network except polluting and on the surface. It’s scaled for minimal ridership, a last-resort mode of transportation for the poorest few percent of workers. The frequency is a fraction of the minimum required to get even semi-reasonable ridership.

Instead, such networks work better when they meet at one city center station, often with timed transfers every half hour or hour. A crosstown line in this situation is useless – it cannot be timed to meet more than one radial, and untimed transfers on buses that come every half hour might as well not even exist. A source who works in planning in Springfield, Massachusetts, a metro area of 600,000, explained to me how the Pioneer Valley Transit Authority (PVTA) bus system works, and nearly all routes are radial around Downtown Springfield or else connect to the universities in the area. There are two circumferential routes within Springfield, both with horrifically little ridership. Providence, too, has little to no circumferential bus service – almost every RIPTA bus goes through Kennedy Plaza, except some outlying routes that stay within a particular suburb or secondary city.

The principle here is that the value of an untimed transfer depends on the frequency of service and to some extent on the quality of station facilities (e.g. shelter). Trains in Prague come every 2-3 minutes at rush hour and every 4-10 minutes off-peak. When the frequency is as low as every 15 minutes, transferring is already questionable; at the typical frequency of buses in a city with a bus-based transportation network, passengers are extremely unlikely to do it.

This raises the question, what about denser bus networks? A city with enough budget for 16 buses running at once is probably going to run 8 radii (four diameters) every half hour, with a city-center timed transfer, and service coverage extending about 24 minutes out of the center in each direction. But what happens if there’s enough budget for 60 buses? What if there’s enough budget for 200 (about comparable to RIPTA)?

Buses are flexible. The cost of inaugurating a new route is low, and this means that there are compelling reasons to add more routes rather than just beef up frequency on every route. It becomes useful to run buses on a grid or mesh once frequency rises to the point that a downtown timed transfer is less valuable. (In theory the value of a timed transfer is scale-invariant, but in practice, on surface buses without much traffic priority, schedules are only accurate to within a few minutes, and holding buses if one of their connections is late slows passengers down more than not bothering with timing the transfers.)

I know of one small city that still has radial buses and a circular line: Växjö. The frequency on the main routes is a bus every 10-15 minutes. But even there, the circular line (bus lines 2 and 6) is a Yamanote-style circle and not a proper circumferential; all of the buses meet in the center of the city. And this is in a geography with a hard limit to the built-up area, about 5-6 km from the center, which reduces the need to run many routes in many different directions over longer distances (the ends of the routes are 15-20 minutes from the center).

There’s also a separate issue, different from scale but intimately bundled with it: mode share. A city with three metro lines is capable of having high transit mode share, and this means that development will follow the lines if it is given the opportunity to. As the three lines intersect in the center, the place for commercial development is then the center. In the communist states that perfected the Soviet triangle, buildings were built where the state wanted them to be built, but the state hardly tried to centralize development. In Stockholm, where the subway would be a triangle but for the three lines meeting at one station, the lack of downtown skyscrapers has led to the creation of Kista, but despite Kista the region remains monocentric.

There is no chance of this happening in a bus city, let alone a bus city with just a handful of radial lines. In a first-world city where public transit consists of buses, the actual main form of transportation is the car. In Stockholm, academics are carless and shop at urban supermarkets; in Växjö, they own cars and shop at big box stores. And that’s Sweden. In the US, the extent of suburbanization and auto-centricity is legendary. Providence has some inner neighborhoods built at pedestrian scale, but even there, car ownership is high, and retail that isn’t interfacing with students (for example, supermarkets) tends to be strip mall-style.

With development happening at automobile scale in smaller cities with smaller transit networks, the center is likely to be weaker. Providence has more downtown skyscrapers than Stockholm, but it is still more polycentric, with much more suburban job sprawl. Stockholm’s development limits in the center lead to a smearing of commercial development to the surrounding neighborhoods (Spotify is headquartered two stops on the Green Line north of T-Centralen, just south of Odengatan). In Providence, there are no relevant development limits; the tallest building in the city is empty, and commercial development moves not to College Hill, but to Warwick.

With a weaker center, buses can’t just serve city center, unless the operating budget is so small there is no money for anything else. This is what forces a bus network that has money for enough buses to run something that looks like a transit network but not enough to add rail to have a complex everywhere-to-everywhere meshes – grids if possible, kludges using available arterial streets otherwise.

This is why bus and rail networks look so profoundly different. Bus grids are common; subway grids don’t exist, except if you squint your eyes in Beijing and Mexico City (and even there, it’s much easier to tell where the CBD is than by looking at the bus map of Chicago or Toronto). But by the same token, the Soviet triangle and near-triangle networks, with a number of important examples among subway network, does not exist on bus networks. The triangle works for cities of a particular size and transit usage intensity, and only in rapid transit, not in surface transit.

Quick Note: U-Shaped Lines

Most subway lines are more or less straight, in the sense of going north-south, east-west, or something in between. However, some deviate from this ideal: for example, circular lines. Circular lines play their own special role in the subway network, and the rest of this post will concern itself only with radial lines. Among the radials, lines are even more common, but some lines are kinked, shaped like an L or a U. Here’s a diagram of a subway system with a prominently U-shaped line:

Alert readers will note the similarity between this diagram and my post from two days ago about the Washington Metro; the reason I’m writing this is that Alex Block proposed what is in effect the above diagram, with the Yellow Line going toward Union Station and then east along H Street.

This is a bad idea, for two reasons. The first is that people travel in lines, not in Us. Passengers going from the west end to the east end will almost certainly just take the blue line, whereas passengers going from the northwest to the northeast will probably drive rather than taking the red line. What the U-shaped layout does it put a one-seat ride on an origin-and-destination pair on which the subway is unlikely to be competitive no matter what, while the pairs on which the subway is more useful, such as northeast to southwest, require a transfer.

The second reason is that if there are U- and L-shaped lines, it’s easy to miss transfers if subsequent lines are built:

The purple line has no connection to the yellow line in this situation. Were the yellow and red line switched at their meeting point, this would not happen: the purple line would intersect each other subway line exactly once. But with a U-shaped red line and a yellow line that’s not especially straight, passengers between the purple and yellow lines have a three-seat ride. Since those lines are parallel, origin-and-destination pairs between the west end of the purple line and east end of the yellow line or vice versa require traveling straight through the CBD, a situation in which the subway is likely to be useful, if service quality is high. This would be perfect for a one-seat or two-seat ride, but unfortunately, the network makes this a three-seat ride.

The depicted purple line is not contrived. Washington-based readers should imagine the depicted purple line as combining the Columbia Pike with some northeast-pointing route under Rhode Island Avenue, maybe with an additional detour through Georgetown not shown on the diagram. This is if anything worse than what I’m showing, because the purple/red/blue transfer point is then Farragut, the most crowded station in the city, with already long walks between the two existing lines (there isn’t even an in-system transfer between them.). Thus the only direct connection between the western end of the purple line (i.e. Columbia Pike) and what would be the eastern end of the yellow line (i.e. H Street going east to Largo) requires transferring at the most crowded point, whereas usually planners should aim to encourage transfers away from the single busiest station.

When I created my Patreon page, I drew an image of a subway network with six radial lines and one circle as my avatar. You don’t need to be a contributor to see the picture: of note, each of the two radials intersects exactly once, and no two lines are tangent. If the twelve ends of six lines are thought of as the twelve hours on a clock, then the connections are 12-6, 1-7, 2-8, 3-9, 4-10, and 5-11. As far as possible, this is what subway networks should aspire to; everything else is a compromise. Whenever there is an opportunity to build a straight line instead of a U- or L-shaped lines, planners should take it, and the same applies to opportunities to convert U- or L-shaped lines to straight ones by switching lines at intersection points.

What Washington Metro Should Build

I’ve been thinking intermittently about how to relieve the capacity crunch on the Washington Metro. The worst peak crowding is on the Orange Line heading eastbound from Arlington to Downtown Washington, and this led to proposals to build a parallel tunnel for the Blue Line. Already a year ago, I had an alternative proposal, borrowing liberally from the ideas of alert reader Devin Bunten, who proposed a separate Yellow Line tunnel instead. Matt Yglesias’s last post about it, using my ideas, made this a bigger topic of discussion, and I’d like to explain my reasoning here.

Here is the map of what I think Metro needs to do:

Existing stations have gray fill, new ones have white fill. The Yellow Line gets its own route to Union Station, either parallel to the Orange Line and then north via the Capitol (which is easier to build) or parallel to the Green Line (which passes closer to the CBD), and then takes over the route to Glenmont. The rump Red Line then gets a tunnel under H Street, hosting the busiest bus in the city, and then takes over the current Blue Line to Largo, with an infill station in Mayfair for a transfer to the Orange Line and another at Minnesota Avenue for bus connections.

The Blue Line no longer presents a reverse-branch. It is reduced to a shuttle between the Pentagon and Rosslyn. Matt mistakenly claims that reducing the Blue Line to a shuttle is cost-free; in fact, it would need dedicated tracks at Rosslyn (if only a single track, based on projected frequency), an expensive retrofit that has also been discussed as part of the separate Blue Line tunnel project. At the Pentagon, initially shared tracks would be okay, since the Yellow Line is still a branch combined with the Green Line today; but the separate Yellow Line tracks would then force dedicated turnback tracks for the Blue Line at the Pentagon as well. Frequency should be high all day, and at times of low frequency (worse than about a train every 6 minutes), the lines in Virginia should be scheduled to permit fast transfers between both the Yellow and Orange Lines and the Blue Line.

The reverse branch today limits train frequency at the peak, because delays on one line propagate to the others. Peak capacity on Metro today is 26 trains per hour. I don’t know of anywhere with reverse-branching and much higher capacity: the London Underground lines that reverse-branch, such as the Northern line, have similar peak traffic, whereas ones that only conventionally branch (Central) or don’t branch at all (Victoria) are capable of 35-36 peak trains per hour. This means that my (and Devin’s, and Matt’s) proposed system allows more capacity even in the tunnel from Rosslyn to Foggy Bottom, which gets no additional connections the way 14th Street Bridge gets to feed a new Yellow Line trunk.

The big drawback of the plan is that the job center of Washington is Farragut, well to the west of the Yellow and Green Lines. WMATA makes origin-and-destination data publicly available, broken down by period. In the morning peak, the top destination station for each of the shared Blue and Yellow Line stations in Virginia is either the Pentagon or Farragut; L’Enfant Plaza is also high, and some stations have strong links to Gallery Place-Chinatown. Metro Center is actually faster to reach by Yellow + Red Line than by taking the Blue Line the long way, but Farragut is not, especially when one factors in transfer time at Gallery Place. The saving grace is that eliminating reverse-branching, turning Metro into four core lines of which no two share tracks, allows running trains more frequently and reliably, so travel time including wait time may not increase much, if at all.

This is why I am proposing the second alternative for the route between L’Enfant Plaza and Union Station. Devin proposed roughly following the legacy rail line. In the 1970s, it would have been better for the region to electrify commuter rail and add infill stops and just run trains on the route, and today a parallel route is appealing; Matt even proposed using the actual rail tunnel, but, even handwaving FRA regulations, that would introduce schedule dependency with intercity trains, making both kinds of trains less reliable. This route, the southeastern option among the two depicted in dashed lines, is easier to build, in that there are multiple possible streets to dig under, including C and E Streets, and giant parking lots and parks where the tracks would turn north toward the Capitol and Union Station. It also offers members of Congress and their staffers a train right to the officeUnfortunately, it forces Farragut-bound riders to transfer to the Orange Line at L’Enfant Plaza, slowing them down even further.

The second alternative means the Yellow Line stays roughly where it is. Four-tracking the shared Yellow and Green Line trunk under 7th Street is possible, but likely expensive. Tunneling under 8th Street is cheaper, but still requires passing under the Smithsonian Art Museum and tunneling under private property (namely, a church) to turn toward H Street. Tunneling under 6th Street instead is much easier, but this is farther from 7th Street than 8th Street is, and is also on the wrong side for walking to Metro Center and points west; the turn to H Street also requires tunneling under a bigger building. By default, the best route within this alternative is most likely 8th Street, then.

A variant on this second alternative would keep the Red Line as is, and connect the Yellow Line to the subway under H Street and to Largo. This is easier to construct than what I depict on my map: the Yellow Line would just go under H Street, with a Union Station stop under the track and new access points from the tracks to a concourse at H Street. This would avoid constructing the turns from the Red Line to H Street next to active track. Unfortunately, the resulting service map would look like a mess, with a U-shaped Red Line and an L-shaped Yellow Line. People travel north-south and east-west, not north-north or south-east.

Under either alternative, H Street would provide subway service to most of the remaining rapid transit-deprived parts of the District west of the Anacostia River. Some remaining areas near the Penn and Camden Lines could benefit from infill on commuter rail, and do not need Metro service. The big gaps in coverage in the District would be east of the river, and Georgetown.

Georgetown is the main impetus for the Blue Line separation idea; unfortunately, there’s no real service need to the east, along K Street, so the separate Blue Line tunnel would be redundant. In the 1970s it would have been prudent to build a Georgetown station between Foggy Bottom and Rosslyn, but this wasn’t done, and fixing it now is too much money for too little extra ridership; Bostonian readers may notice that a similar situation arises at the Seaport and BCEC, which should be on the Red Line if it were built from scratch today, but are unserved since the Red Line did not go there in the 1900s and 10s, and attempting to fix it by giving them their own subway line is a waste of money.

East of the river, the Minnesota Avenue corridor would make a nice circumferential rapid bus. But there are no strong radial routes to be built through it; the strongest bus corridor, Pennsylvania Avenue, serves a small node at the intersection with Minnesota and thereafter peters out into low-frequency branches.

This means that if the Yellow Line separation I’m proposing is built, all parts of the District that could reasonably be served by Metro will be. If this happens, Metro will have trunk lines with frequent service, two not branching at all and two having two branches on one side each; with passengers from Alexandria riding the Yellow Line, the Orange crush will end. The main issue for Metro will then be encouraging TOD to promote more ridership, and upgrading systems incrementally to allow each trunk line to carry more trains, going from 26 peak trains per hour to 30 and thence 36. Washington could have a solid rapid transit skeleton, which it doesn’t today, and then work on shaping its systems and urban layout to maximize its use.

RPA Fourth Regional Plan: LaGuardia Airport and the Astoria Line

This is the second post based on a Patreon poll about the RPA Fourth Regional Plan. See the first post, about Third Avenue, here.

The most worrisome part of the RPA Fourth Regional Plan is the LaGuardia Airport connector. The regional rail system the RPA is proposing includes some truly massive wastes of money, but what the RPA is proposing around LaGuardia showcases the worst aspects of the plan. On Curbed I explained that the plan has an unfortunate tendency to throw in every single politically-supported proposal. I’d like to expand on what I said in the article about the airport connector:

The most egregious example is another transit project favored by a political heavyweight: the LaGuardia AirTrain, championed by Governor Andrew Cuomo. Though he touts it as a one-seat ride from Midtown to LaGuardia, the vast majority of airport travelers going to Manhattan would have to go east to Willets Point (a potential redevelopment site) before they could go west. Even airport employees would have to backtrack to get to their homes in Jackson Heights and surrounding neighborhoods. As a result, it wouldn’t save airport riders any time over the existing buses.

Once again, it’s proven unpopular with transit experts and advocates: [Ben] Kabak mocked the idea as vaporware, and Yonah Freemark showed how circuitous this link would be. When Cuomo first proposed this idea, Politico cited a number of additional people who study public transportation in the region with negative reactions. Despite its unpopularity—and the lack of an official cost for the proposal—the AirTrain LaGuardia is included in the RPA’s latest plan.

But there is an alternative to Cuomo’s plan: an extension of the N/W train, proposed in the 1990s, which would provide a direct route along with additional stops within Astoria, where there is demand for subway service. Community opposition killed the original proposal, but a lot can change in 15 years; Astoria’s current residents may well be more amenable to an airport connector that would put them mere minutes from LaGuardia. Cuomo never even tried, deliberately shying away from this populated area.

And the Fourth Plan does include a number of subway extensions, some of which have long been on official and unofficial wishlists. Those include extensions under Utica and Nostrand avenues (planned together with Second Avenue Subway, going back to the 1950s), which also go under two of the top bus routes in the city, per [Jarrett] Walker’s maxim [that the best argument for an urban rail line is an overcrowded bus line, as on Utica and Nostrand].

There is also an extension of the N/W trains in Astoria—though not toward LaGuardia, but west, toward the waterfront, where it would provide a circuitous route to Manhattan. In effect, the RPA is proposing to stoke the community opposition Cuomo was afraid of, but still build the easy—and unsupported—airport connector Cuomo favors.

My views of extending the Astoria Line toward LaGuardia have evolved in the last few years, in a more positive direction. In my first crayon, which I drew in 2010, I didn’t even have that extension; I believed that the Astoria Line should be extended on Astoria Boulevard and miss the airport entirely, because Astoria Boulevard was the more important corridor. My spite map from 2010, give or take a year, connects LGA to the subway via a shuttle under Junction, and has a subway branch under Northern, a subway extension that I’ve been revising my views of negatively.

The issue, to me, is one of branching and capacity. The Astoria Line is a trunk line on the subway, feeding an entire tunnel to Manhattan, under 60th Street; the Queens Boulevard Line also feeds the same tunnel via the R train, but this is inefficient, since there are four trunk lines (Astoria, Flushing, and Queens Boulevard times two since it has four tracks), four tunnels (63rd, 60th, 53rd, Steinway/42nd), and no way to get from the Astoria Line to the other tunnels. This was one of my impetuses for writing about the problems associated with reverse-branching. Among the four trunks in Queens, the Astoria Line is the shortest and lowest-ridership, so it should be extended deeper into Queens if it is possible to do so.

The RPA is proposing to extend the Astoria Line, to its credit. But its extension goes west, to the waterfront. This isn’t really a compelling destination. Development isn’t any more intense than farther east, and for obvious reasons it isn’t possible to extend this line further; the RPA’s proposal would only add one stop to the subway. In contrast, an eastern extension toward LGA could potentially rebuild the line to turn east on Ditmars (with some takings on the interior of the curve at Ditmars and 31st), with stops at Steinway and Hazen before serving the airport. The intensity of development at Steinway is similar to that at 31st and Ditmars or at 21st, and Hazen also has some housing, albeit at lower density. Then, there is the airport, which would be about 8 minutes from Astoria, and 26 minutes from 57th and 7th in Manhattan. This is a different route from that proposed in the Giuliani administration, involving going north above 31st and then east farther out, running nonstop to the airport (or perhaps serving a station or two) through less residential areas, but I believe it is the best one despite the added impact of running elevated on Ditmars.

LGA is not a huge ridership generator; total O&D ridership according to the Consumer Airfare Report is around 55,000 per day, and 33% mode share is aspirational even with fast direct service to Manhattan hotels and an easy connection to the Upper East Side. But it still provides ridership comparable to that of Astoria Boulevard or Ditmars on the line today, and Steinway and Hazen are likely to add more demand. If the MTA closes the 11th Street Connection, taking the R from 60th Street Tunnel to the Queens Boulevard Line, in order to reduce the extent of reverse-branching, then the Astoria Line will run under capacity and need this additional demand. The total number of boardings at all stations, including Queensboro Plaza, is 80,000 per weekday today, plus some transfer volumes from the 7, which empties at Queensboro Plaza as 60th Street Tunnel provides a faster route to most Manhattan destinations than the Steinway Tunnel. An LGA extension should add maybe 40,000 or 50,000 weekday riders, without much of a peak since airport travel isn’t peaky, and make it easier to isolate the Astoria Line from the other Queens lines. This is not possible with a short extension to the waterfront as the RPA proposes.

I’ve seen someone suggest somewhere I don’t remember, perhaps on Twitter, that the reason the RPA plan involves an extension of the Astoria line to the west is to insidiously get the correct extension to LGA passed. If the RPA can propose an el in Astoria and not be killed by NIMBYs, then it will prove to Cuomo that NIMBYism is not a problem and thus he can send the subway to the airport directly, without the circuitous air train project that even less acerbic transit writers like Ben and Yonah hate.

I disagree with this line, on two different grounds. The first is that the RPA has two other reasons to support a western extension of the Astoria Line: it connects to the waterfront (which, following de Blasio and his support for the waterfront tramway, the RPA wants to develop further), and it got a station on Triboro in the Third Regional Plan, in the 1990s. I can no longer find the map with the stations on Mike Frumin’s blog, but the plan was to have a station every 800 meters, with a station to the west of Ditmar/31st still in Queens, around 21st Street; only in the more recent plan did the RPA redesign the idea as Crossboro, with much wider stop spacing.

The second grounds for disagreement is that the RPA presented a long-term vision. If Cuomo’s flawed LGA connector is there, then it will embolden him to find money to build this connection, even though it’s slower than taking a bus to the subway today. It will not embolden anyone to look for funding for the extension of the Astoria Line to the west, since there is no force clamoring for such extension – not the neighborhood, and not even the RPA, which includes this line on a long list of proposals.

As I said on Curbed, the RPA has been around for 90 years. Cuomo is just a governor, not even the leader of a real political movement (unlike Bernie Sanders, who seems to be interested in his leftist agenda more than in himself). There is no reason for an organization so venerable to tether itself to a politician who isn’t likely to be around for more than a few more years. On the contrary, it can provide cover for Cuomo to change his plan, if it does some legwork to prove that people in Astoria actually are interested in subway expansion to the east.

Elon Musk’s Ideas About Transportation are Boring

Four years ago, I broke my comment section by declaring that Elon Musk’s Hyperloop proposal had no merit, combining technical criticism with expressions like “barf ride” and “loopy.” Since then, Musk seems to have quietly abandoned Hyperloop, while the companies attempting to build the technology, run by more serious people, are doing away with the promise of reducing construction costs to one tenth those of conventional high-speed rail. Instead, Musk has moved to a new shiny target in his quest to sell cars and compete with public transit: The Boring Company. I criticized some of what he was saying in Urbanize.LA last summer, but I’d like to go into more detail here, in light of a new fawning interview in Wired and an ensuing Twitter flamewar with Jarrett Walker. In short, Musk,

a) has little understanding of the drivers of tunneling costs,
b) promises reducing tunneling costs by a factor of 10, a feat that he himself has no chance to achieve, and
c) is unaware that the cost reduction he promises, relative to American construction costs, has already been achieved in a number of countries.

The Boring Company’s Ideas of How to Cut Costs

There is much less technical information available publicly than there was for Hyperloop. However, The Boring Company has an FAQ including an outline of how it aims to cut construction costs:

First, reduce the tunnel diameter. The current standard for a one-lane tunnel is approximately 28 feet. By placing vehicles on a stabilized electric skate, the diameter can be reduced to less than 14 feet. Reducing the diameter in half reduces tunneling costs by 3-4 times. Second, increase the speed of the Tunnel Boring Machine (TBM). TBMs are super slow. A snail is effectively 14 times faster than a soft-soil TBM.  Our goal is to defeat the snail in a race. Ways to increase TBM speed:

  • Increase TBM power. The machine’s power output can be tripled (while coupled with the appropriate upgrades in cooling systems).
  • Continuously tunnel. When building a tunnel, current soft-soil machines tunnel for 50% of the time and erect tunnel support structures the other 50%. This is inefficient. Existing technology can be modified to support continuous tunneling activity.
  • Automate the TBM. While smaller diameter tunneling machines are automated, larger ones currently require multiple human operators. By automating the larger TBMs, both safety and efficiency are increased.
  • Go electric. Current tunnel operations often include diesel locomotives. These can be replaced by electric vehicles.
  • Tunneling R&D. In the United States, there is virtually no investment in tunneling Research and Development (and in many other forms of construction).  Thus, the construction industry is one of the only sectors in our economy that has not improved its productivity in the last 50 years.

This is not the first time that Musk thinks he can save a lot of money by reducing tunnel diameter; he said the same thing in the Hyperloop paper. Unfortunately for him, there is literature on the subject, which directly contradicts what he says. In my Urbanize piece, I mention a study done for the Very Large Hadron Collider, which compares different tunnel diameters across various soil types, on PDF-p. 5. Two tunnel diameters are compared, 4.9 m (16′) and 3.9 (12′). Depending on soil type and tunnel boring machine (TBM) drive, the larger tunnel, with 1/3 larger diameter, costs 15-32% more.

Subsequent pages in the study break down the costs per item. The TBM itself has a cost that scales with cross-sectional area, but is only a small minority of the overall cost. The study assumes five drives per TBM, with the first drive accounting for 75% of the TBM’s capital cost; in the first drive the larger-diameter tunnel is 32% more expensive, since the TBM accounts for 25-40% of total cost depending on diameter and rock, but in subsequent drives the TBM accounts for about 5% of total cost. Another 6% is muck cars (item 2.05, PDF-pp. 7 and 46), whose cost rises less than linearly in tunnel diameter. The rest is dominated by labor and materials that are insensitive to tunnel width, such as interior lighting and cables.

But the actual cost is even less sensitive to tunnel width. The VLHC study only looks at the cost of tunneling itself. In addition, there must be substantial engineering. This is especially true in the places where transportation tunnels are most likely to arise: mountain crossings (for intercity rail), and urban areas (for urban rail and road tunnels). This is why there’s a trend toward bigger tunnels, as a cost saving mechanism: BART’s San Jose extension is studying different tunnel approaches, one with a large-diameter tunnel and one with twin small-diameter tunnels, and the cost turns out to be similar. In Barcelona, the large-diameter TBM actually saved money and reduced disruption in construction.

The Boring Company’s various bullet points after its point about tunnel diameter are irrelevant, too. For example, labor is a substantial portion of TBM costs, but in the VLHC study it’s about one third of the cost in easier rock and 15% in harder rock. There appears to be a lot of union featherbedding in some American cities, but this is a political rather than technological problem; without such featherbedding, labor costs are not onerous.

Tunneling Costs Aren’t Just Boring

At $10 billion for just 2.2 km of new tunnel, East Side Access is the most expensive urban rail tunnel I am aware of. The second most expensive, Second Avenue Subway’s first phase, costs $1.7 billion per km, not much more than a third as much. Is New York really spending $10 billion on just boring 2.2 km of tunnel? Of course not. The 2 km in Manhattan cost a little more than $400 million, per an MTA status report from 2012 (PDF-p. 7). The few hundred meters in Queens actually cost more, in an unnecessary tunnel under a railyard. The cavern under Grand Central cost much more, as do ancillary structures such as ventilation.

The TBM is probably the most technologically advanced portion of urban tunneling today. Even in New York, in the most expensive project ever built, the TBM itself is only responsible for about $200 million per km; more typical costs, cited in a consultant’s report for Rocky Mountain tunneling, are somewhat less than $100 million per km. This is why large-diameter TBMs are so appealing: they increase the cost of the tunneling itself, but save money everywhere else by allowing stations to be constructed within the bore.

Of course, The Boring Company is not building conventional subways. Subways already exist, and Musk likes reinventing everything from the wheel onward. Instead, the plan is to build tunnels carrying cars. This means several things. First, the capacity would be very low, especially at the proposed speed (Musk wants the cars to travel at 200 km/h – excessive speed is another of his hallmarks).

Second and more importantly, instead of having to deal with expensive subway stations, the infrastructure would have to deal with expensive ramps. Musk wants cars to be lowered into the tunnels with elevators. Underground elevators are cheap (vertical TBMs are easy), but in the proposed application they just move the problem of ramps deeper underground: the elevator (“skate” in Musk’s terminology) would carry the cars down, but then they’d need to accelerate from a standstill to line speed, in new tunnels, separate from the mainline tunnels so as to avoid slowing down through-traffic. Trains solve this problem by making the entire train stop in the tunnel and taking the hit to capacity, and compensating by running a long train with many more people than cars could possibly hold. But roads would need the same infrastructure of urban freeways, underground.

Switching between tunnel trunks poses the same problem. Flying junctions are expensive, especially underground. In New York, they were common on the IND subway, built in the late 1920s and 1930s; the IND was expensive for its time, around $150 million per route-km in today’s money, whereas the Dual Contracts from the 1910s and early 20s (with fewer junctions) were about $80 million per underground route-km. Most subway systems don’t do what the IND did, and instead of complex junctions they build independent lines, switching between them using transfer stations. With cars, this solution is impossible, forcing underground four-level interchanges; even above ground, those interchanges cost well into the 9 figures, each.

There is So Much Musk Doesn’t Know

The starting point of The Boring Company is that Los Angeles’s tunnel construction costs, which the company pegs at a billion dollars per mile, need to be reduced by a factor of ten. This means cutting them from about $600 million per km to $60 million. While there is nothing that Musk or his company has said in public that suggests he is capable of reducing construction costs, other parts of the world have substantially done so already.

In my construction costs posts, there are a few projects in the $60 million/km area. Manuel Melis Maynar, the former CEO of Madrid Metro, wrote a brief report on how he built subways cheaply; in today’s money, the underground parts of Madrid’s 1999-2003 subway expansion cost around $70 million per km, but this includes rolling stock, and without it, actual cost is likely to be where Musk wants it to be. Recent subway lines in Seoul have also been in that area, including Metro Line 9 and the Sin-Bundang Line. Going up to $100 million per km, there are more lines in Stockholm.

Melis Maynar’s writeup ignores any of the technological pizzazz Musk thinks of. Instead of trying to squeeze more power out of TBM, he emphasizes good contracting practices, and separation of design and construction. Like Musk, he believes that faster construction is cheaper, but he is aware that the limiting factor is not boring speed: even at a conservative rate of 15 meters per day, a TBM could excavate several kilometers a year, so it’s better instead to begin construction at several points along the line and work in parallel rather than in sequence. Adding TBMs does not make projects substantially more expensive: one TBM used for East Side Access cost $6-8 million, and other estimates I’ve seen only reach into the 8 figures, for multibillion dollar projects. Nor does adding staging areas raise cost underground, where there are many potential sites; underwater it’s a bigger problem, and there costs are indeed much higher, but nothing that Musk does seems designed around underwater tunnels, and his proposed map for LA road tunnels is underground.

Musk’s Ideas: Loopy and Boring

Americans hate being behind. The form of right-wing populism that succeeded in the United States made that explicit: Make America Great Again. Culturally, this exists outside populism as well, for example in Gordon Gekko’s greed is good speech, which begins, “America has become a second-rate power.” In the late 2000s, Americans interested in transportation had to embarrassingly admit that public transit was better in Europe and East Asia, especially in its sexiest form, the high-speed trains. Musk came in and offered something Americans craved: an American way to do better, without having to learn anything about what the Europeans and Asians do. Musk himself is from South Africa, but Americans have always been more tolerant of long-settled immigrants than of foreigners.

In the era of Trump, this kind of nationalism is often characterized as the domain of the uneducated: Trump did the best among non-college-educated whites, and cut into Democratic margins with low-income whites (regardless of education). But software engineers making $120,000 a year in San Francisco or Boston are no less nationalistic – their nationalism just takes a less vulgar form. Among the tech workers themselves, technical discussions are possible; some close-mindedly respond to every criticism with “they also laughed at SpaceX,” others try to engage (e.g. Hyperloop One). But in the tech press, the response is uniformly sycophantic: Musk is a genius, offering salvation to the monolingual American, steeped in the cultural idea of the outside inventor who doesn’t need to know anything about existing technology and can substitute personal intelligence and bravery.

In reality, The Boring Company offers nothing of this sort. It is in the awkward position of being both wrong and unoriginal: unoriginal because its mission of reducing construction costs from American levels has already been achieved, and wrong because its own ideas of how to do so range from trivial to counterproductive. It has good marketing, buoyed by the tech world’s desire to believe that its internal methods and culture can solve every problem, but it has no product to speak of. What it’s selling is not just wrong, but boringly so, without any potential for salvaging its ideas for something more useful.

There’s More Redundancy Than You Think

I was visiting Boston last week, and am in New York this week; you can see me at NYU on Thursday tomorrow. Last week, I met with TransitMatters activists talking about bus and rail improvements in Boston, and on the way saw something that made me understand two things. First, the MBTA is run by incompetent people. And second, even two subway lines that are perpendicular and serve completely different areas can be redundant with each other.

Two and a half years ago, I said redundancy is overrated. In this post, I’d like to argue from the opposite direction: transit networks have more redundancy than they appear to. One implication is identical to that of my older post: transit agencies should build subway lines without regard for redundant service, since not only is redundancy overrated, but also a new subway line is redundant with old lines even if they serve completely different areas. But the other implication concerns service interruptions and shutdowns.

The issue in Boston is that, although there are nighttime shutdowns, there are also occasional weekend shutdowns, as in New York, for major capital projects. The Red Line is being closed on weekends for two months on the segment between Boston proper and Cambridge. But the Orange Line is also being closed on weekends on segments, after deferred maintenance led to a meltdown in the last two months, with frequent delays and slow zones. Last weekend, I found myself having to go between Davis Square (on the Red Line, just off the edge of the map) and Jamaica Plain (near the bottom of the Orange Line) to visit Sandy Johnston, with the highlit segments shut down:

Shuttle buses replaced the subway on both segments. On the Red Line, the MBTA contracted it out to a private company that used wheelchair-inaccessible high-floor buses; there were not enough MBTA bus drivers to run the shuttles on both segments, and by union rules the MBTA could not use contract drivers on its own buses even though it did have the equipment, forcing it to use inferior private-sector buses. I am able-bodied enough to climb high-floor buses, but I would not use the shuttle buses replacing the Red Line for another reason: as can be seen in the map, there is no continuous street grid between Charles/MGH and Park Street. If there were a crossover right east of Charles/MGH then only the Kendall-MGH segment would be bustituted, and there, the buses would go on Longfellow Bridge, with a serious but not fatal slowdown. But between Kendall and Park Street the buses have to swerve through side streets that were not designed for fast traffic; in 2012, I was on such a shuttle and as I recall the trip took 15 or 20 minutes, where the subway does it in about 5.

Instead of relying on shuttles, I took a bus north of the river to get to Lechmere and use the Green Line to reach Chinatown on a chain trip. From Chinatown the options were all bad, and I rode the 39 bus, which parallels the Green Line E Branch (the southernmost one) and continues south to Forest Hills, where the Green Line once ran as well. The way back was not a chain trip, and with a bus-bus-Red Line trip and no 39 bus in sight (the online bus tracker was down), I gave up and took a taxi.

The Red Line and Orange Line look like they go in different directions, so shutting down one does not affect the other. But in reality, in a city with buses, taking the bus to a different line is a common strategy to deal with shutdowns – hence, using the Green Line to get between Davis and Chinatown, taking a bus in a place where the buses are less slow than between Charles/MGH and Park Street.

If any city in North America did not use buses at all, it would be Boston. It has legendarily narrow and twisted streets, and crawling buses. It has higher rail-to-bus ridership ratio than any other American city except possibly New York, and far higher ratio than the major English Canadian cities with their bus grids. Its transit network, inherited from midcentury, uses the buses to feed the subway, and has no bus service through downtown, where even before mass motorization there were traffic jams of streetcars.

But even in Boston, using the bus outside the core to get to a better subway line is possible, and normal when there are service interruptions. This means that any pair of subway lines could potentially be redundant with each other. This means that it is bad practice to shut down more than one line at once for repairs. The reason the Orange Line needs emergency repairs in the first place is that the MBTA maintained it poorly and wouldn’t act when it was less urgent, such as six months ago (Sandy reports noticing a consistent deterioration in service since January). Today, the shutdowns are probably unavoidable. But the Red Line shutdowns, for a capital construction project involving the Longfellow Bridge, can be delayed. The MBTA should do that in the future in order to both avoid having to use inaccessible buses and allow passengers to take a circumferential bus to a functioning subway line.

Fix DeKalb Avenue

In New York, there are two dedicated subway tracks on the Manhattan Bridge offering a bypass of Lower Manhattan. Between DeKalb Avenue in Brooklyn and Canal Street in Chinatown in Manhattan, Q trains run nonstop for 3.5 km, while the R train goes the long way, taking 5.5 km and making 2 intermediate stops in Downtown Brooklyn and 4 in Lower Manhattan. The N skips DeKalb Avenue, with a 4.5 km nonstop segment between Canal Street and the Atlantic/Pacific/Barclays station complex.

The Q and N should be immense time savers. Instead, the Q does the trip in 8 minutes and the N in 10, both of which average 26-27 km/h. The subway’s overall average speed, weighed down by local trains stopping every 700 meters, is 29 km/h. The Q and N are still time savers, though, because the R does the 5.5 km in 18 minutes, an average speed of 16 km/h – far less than the systemwide average, and even less than the slowest Paris Metro line, Line 4 with its 500-meter interstations and 20 km/h average speed. Between DeKalb and Pacific, about 800 meters, the R takes 3 minutes. Unfortunately, New York City Transit is not taking any measures that would fix this, and when I asked about one possibility, I got excuses.

There are two reasons why this part of the subway is so slow. The first is something called signal timers. Timers are devices installed at frequent intervals on long interstations, such as the bridges and tunnels connecting Manhattan with Brooklyn and Queens, limiting train speed. These timers have always been around, but after fatal accidents in the 1990s, New York City Transit tightened them, reducing speed further; for some more background, see my Vox piece from last summer. The timers are more safety theater than safety. The biggest conclusion I reached from looking at the accident postmortem on the NTSB and some NYCT information was “make sure your trains’ brakes work as intended”; NYCT derated the trains’ service and emergency braking rates later in the 90s, which marginally reduces maintenance costs but is bad for safety and brutal for train speed.

The second reason is the switches at DeKalb Avenue. DeKalb is a six-track station, with four tracks feeding the Manhattan Bridge and two feeding the tunnel through Lower Manhattan. The two tunnel tracks then continue to the south as local tracks on the Fourth Avenue Line, carrying the R; this is the least used of all subway trunk lines into Manhattan, because the detour and low speed make it useless for most Midtown-bound passengers. The four bridge tracks include two express tracks at DeKalb going to the Brighton Line, and two super-express tracks skipping DeKalb continuing to the south as express Fourth Avenue tracks. Today, there is a splitting and recombining of branches. The B and D run together from Sixth Avenue to the Manhattan Bridge, and the N and Q run together from Broadway, but just north of DeKalb they recombine as B and Q running to Brighton, and D and N running super-express down Fourth Avenue.

This recombination at DeKalb slows down trains considerably, in two ways. First, the interlocking is complex. You can see it on this map on NYCSubway.org; in addition to splitting and recombining the B, D, N, and Q, it also has a non-revenue connection allowing R trains to serve the Brighton Line. Trains on diverging turnouts go at glacial speeds. And second, trains from four lines influence one another’s schedules, and delays propagate. Supervising train movements is thus difficult, and control center has to have a camera watching the trains enter the interlocking to ensure they adhere to schedule; timetables have to take the resulting delays into account.

When I first complained about reverse-branching in New York, I talked about capacity limits imposed by having more trunk lines than branches, a situation that is still to some extent true going north and east of Midtown. At DeKalb, there are six tracks going in and six going out, but the recombination makes things slower, and should be removed. NYCT should make a decision between having B and D trains run on the Brighton Line and the N and Q on Fourth Avenue, or the reverse. The interlocking permits either option, with entirely grade-separated junctions, allowing the trains on the two lines to no longer interfere with each other’s operations.

I in fact asked NYCT about it by proxy. NYCT dismissed the idea, on the grounds that transfer volumes between the B/D and N/Q would be too big. At Atlantic/Pacific, the Pacific side has a cross-platform transfer between the local R and express D/N, but going between the Pacific side and the Atlantic side (the B/Q, and separately the 2/3/4/5) involves a lot of walking. NYCT believes that passengers would flood the corridors looking for a train to their preferred destination, and the transfer volumes would require trains to have long dwell times. NYCT said nothing about whether the overall speed would actually fall, but I believe that based on the large transfer volumes NYCT predicts, passenger trip times (including transfer times) would rise. The only problem: I don’t believe NYCT’s prediction is true at all.

The B and D trains go express up Sixth Avenue, making stops at Grand Street in Chinatown, Broadway-Lafayette on Houston Street, West Fourth Street in the Village, and Herald Square. The N and Q trains go express up Broadway, serving Canal Street in Chinatown, Union Square, and Herald Square. North of Herald Square the two lines are never more than one long block apart until they leave Midtown. Passengers going toward Midtown are unlikely to have strong opinions about which of the two lines they would prefer.

Passengers going to destinations between Manhattan Bridge and Midtown might register stronger preferences. Union Square is the fourth busiest subway station in New York, and is quite far from the B and D. The closest alternative using the B and D is to change cross-platform to the M or F at West Fourth, and get off at 14th Street and Sixth Avenue, two long blocks from Union Square. Three more stations are potential concerns: Canal Street ranks 18th, West Fourth ranks 21st, and Broadway-Lafayette ranks 25th. Getting to Broadway-Lafayette from the N or Q is easy: the station and Canal Street are both on the 6, and passengers can transfer to the 6 at Canal.

West Fourth and Canal remain concerns, but they are not huge ones; they are secondary destinations. Canal is only a major destination for Chinese-New Yorkers, and in Brooklyn they cluster in Sunset Park along Fourth Avenue, suggesting that the Fourth Avenue express tracks should carry the N and Q and the Brighton tracks should carry the B and D. The urban geography of Chinese-New Yorkers is changing due to the combination of fast immigration and fast integration and migration to the suburbs, but this is a service decision, not an infrastructure investment; it can be reversed if demographics change.

Moreover, as a destination, West Fourth is predominantly used for NYU. The Village is a dense residential neighborhood, and West Fourth allows its residents to easily reach Lower Manhattan, Downtown Brooklyn, and two different four-track trunk lines through Midtown. But it has few jobs, outside NYU, which lies mostly between Sixth Avenue and Broadway. Union Square can adequately serve people going toward NYU, and stations on the R and 6 to the south can serve people going to NYU even better. The one problem is that the transfer between the R and the N/Q at Canal Street is not cross-platform; the cross-platform transfers start at Union Square. But with coverage of multiple stations walkable to NYU, the loss of the one-seat ride to West Fourth is not fatal. Even the transfer to the A, C, and E trains at West Fourth has alternative options: passengers from the N or Q going to the E can transfer to the F or M at Herald Square and reach the same stations, and passengers going to the A or C can transfer to the 1 at Times Square and to the A or C at Columbus Circle, both of which transfers are not much harder than climbing two flights of stairs at West Fourth.

With so many options, not many riders would be connecting at Atlantic/Pacific, and trains could keep dwell times short. If anything, dwell times might be shorter, because missing a train would be less fatal: the next train on the same track would serve the same destinations in Midtown, so riders would only need to wait about 3 minutes at rush hour, and 5 minutes off-peak. The gain in speed would be substantial, with the interlocking imposing fewer operational constraints.

NYCT might need to slightly rework the switches, to make sure the chosen matching of the lines in Manhattan and Brooklyn takes the straight and not the diverging direction at the turnouts; typically, the straight direction imposes no speed limit (up to full line speed on high-speed rail lines), but the diverging direction is slow. A matching in which the B and D go on Brighton and the N and Q on Fourth Avenue express to my understanding already involves only one diverging move, if I am reading the track map linked on NYCSubway.org correctly. At the same time, NYCT could fix the switches leading to the R: there was through-service from the Brighton Line to the tunnel tracks the R uses today, but there no longer is, so this out-of-service connection should get diverging and not straight moves. But even with the R, the capital investment involved is minimal.

I do not know the potential travel time gains between DeKalb and Canal Street (or Grand Street) with no timers or reverse-branching. With straight tracks across Manhattan Bridge, and wide curves toward Grand Street, 3.5-minute trips are aspirational, 4-minute trips are still possible, and 5-minute trips should be easy. From Pacific Street, add one more minute, corresponding to cruising at 50 km/h, a speed limit the subway routinely attains even on local tracks. This saves passengers from DeKalb about 4 minutes, and passengers from Pacific about 5. The average trip across the system is about 21 minutes, and the average delay (“excess journey time“) is 3 minutes. The saving would be immense, and contribute to both more casual ridership between Brooklyn and Manhattan, and lower operating costs coming from faster trips.

NYCT should not make excuses for this. The timers may have been originally justified as a safety improvement, but reducing train braking rates had the opposite effect. And, uniquely among the various reverse-branch points in New York, DeKalb feeds two Manhattan trunks that are very close to each other, especially in Midtown, to the point that one-seat rides to every stop have limited value. It should make a decision about whether to run the B/D together on Fourth Avenue and the N/Q on Brighton (switching the Q and D) or the reverse (switching the B and N), based on origin-and-destination data. Some passengers might bemoan the loss of one-seat rides, but most would cheer seeing their trips sped up by 4-5 minutes.

Little Things That Matter: Vertical Circulation

Chatelet-Les Halles has a problem with passenger circulation. It has exceedingly wide platforms – the main platforms, used by the RER A and B, are 17 meters wide – but getting between the platform level and the rest of the station runs into a bottleneck. There are not enough stairs and escalators between the platform and the mezzanine, and as a result, queues develop after every train arrival at rush hour. Similar queues are observed at the Gare du Nord RER platforms. The situation at Les Halles is especially frustrating, since it’s not a constrained station. The platforms are so wide they could very easily have four or even six escalators per access point flanking a wide staircase; instead, there are only two escalators, an acceptable situation at most stations but not at a station as important as Les Halles.

This is generally an underrated concern in the largest cities. In smaller cities, the minimum number of access points required for coverage (e.g. one per short subway platform, two per long platform) is enough even at rush hour. But once daily ridership at a station goes into the high five figures or the six figures, a crunch is unavoidable.

There are two degrees of crunch. The first, and worse, is when the capacity of the escalators and stairs is not enough to clear all passengers until the next train arrives. In practice, this forces trains to come less often, or to spread across more platforms than otherwise necessary; Penn Station’s New Jersey Transit platforms are that bad. The situation at Les Halles and Gare du Nord is a second, less bad degree of crunch: passengers clear the platform well before the next train arrives, but there’s nonetheless a significant queue at the bottom of the escalator pits. This adds 30-60 seconds to passenger trip times, a nontrivial proportion of total trip time (it’s a few percent for passengers within the city and inner suburbs). Avoiding even the less bad crunch thus has noticeable benefits to passengers.

The capacity of a horizontal walkway is 81 passengers per minute per meter of width (link, p. 7-10). This is for bidirectional travel. Unidirectional capacity is a little higher, multidirectional capacity a little lower. Subway platforms and passages are typically around 5 meters wide, so they can move 400 passengers per minute – maybe a little more since the big crunch is passengers heading out, so it’s unidirectional with a few salmons (passengers arrive at the station uniformly but leave in clumps when the train arrives). Busier stations often have exits at opposite ends of the platform, so it’s really 400*2 = 800. Queues are unlikely to form, since trains at best arrive 2 minutes apart, and it’s uncommon for a train to both be full and unload all passengers at one station.

An escalator step can be 60 cm, 80 cm, or 1 meter wide, with another 60 cm of handrail and gear space on both sides. On public transit, only the widest option is used, giving 1.6 meters of width. The theoretical capacity is 9,000 passengers per hour, but the practical capacity is 6,000-7,000 (link, p. 13), or 100-120 per minute. This is more than pedestrian walking capacity per unit of step width, but less per unit of escalator pit width. So a pedestrian walkway ending in a battery of escalators will have a queue, unless the width of the escalator bank is more than that of the walkway leading to it.

Moreover, escalators aren’t just at the end of the station. The busiest train stations have multiple access points per platform, to spread the alighting passengers across different sections of the platform. But mid-platform access points have inherently lower capacity, since they compete for scarce platform width with horizontal circulation. It appears that leaving around 2 meters on each side, and dedicating the rest to vertical circulation, is enough to guarantee convenient passenger access to the entire platform; in a crunch, most passengers take the first access point up, especially if there’s a mezzanine (which there is at Les Halles).

Should New York invest in better commuter rail operations, it will face a bigger risk of queues than Paris has. This is for two reasons. First, New York has much higher job density in Midtown than Paris has anywhere, about 200,000/km^2 vs. perhaps 100,000 around La Defense and the Opera (my figures for both areas in Paris have huge fudge factors; my figure for New York comes from OnTheMap and is exact). And second, Manhattan’s north-south orientation makes it difficult to spread demand across multiple CBD stations on many commuter rail lines. One of the underrated features of a Penn Station-Grand Central connection is that through-trains would have passengers spread across two CBD stops, but other through-running regional rail lines would not have even that – at best they’d serve multiple CBDs, with one Midtown stop (e.g. my line 4 here).

When I computed the needs for vertical circulation at a Fulton Street regional rail station in this post, I was just trying to avoid the worse kind of crunch, coming up with a way to include 16 platform-end escalators (12 up, 4 down in the morning peak) and 16 mid-platform escalators (8 up, 8 down) on a 300-meter long two-level station. It’s likely that the escalator requirement should be higher, to avoid delaying passengers by 1-1.5 minutes at a time. With four tracks (two on a Grand Central-Staten Island line, two on a Pavonia-Brooklyn line) and 12-car trains arriving every 2 minutes, in theory the station could see 240,000 incoming passengers per hour, or 4,000 per minute. In reality, splitting passengers between Grand Central and the Financial District on what I call line 4 means that a sizable majority of riders wouldn’t be getting off in Lower Manhattan. When I tried to compute capacity needs I used a limit passenger volume of 120,000 per hour, and given Midtown’s prominence over Lower Manhattan, even 90,000 is defensible.

90,000 per hour is still 1,500 per minute, or 3,000-4,000 if we are to avoid minute-long queues. A single up escalator is limited to about 100-120 people per minute, which means that twenty up escalators is too little; thirty or even forty are needed. This requires a wider platform, not for horizontal passenger circulation or for safety, but purely for escalator space, the limiting factor. I proposed an 8-meter platform, with space for four escalators per end (two ends per platform, two platforms on two different levels), but this suggests the tube diameter should be bigger, to allow 10-meter platforms and six escalators per end, giving four up escalators per end. This is 16 up escalators. Another 16-20 up escalators can be provided mid-platform: the plan for eight up escalators involved eight access points interspersed along the platform, and 10-meter platforms are wide enough width to include three escalators (two up, one down) per bank and on the border of allowing four (three up, one down).

The situation at the Midtown stations in New York is less constrained. Expected volumes are higher, but Grand Central and Penn Station both spread passengers among multiple platforms. In the near term, Penn Station needs to add more vertical circulation at the New Jersey Transit platforms. The LIRR remodeled its section of the station to add more access points in the 1990s (e.g. West End Concourse), but New Jersey Transit is only doing so now, as part of phase 1 of Moynihan Station, and it’s still not adding as many, since its platforms are shorter and don’t extend as far to the west.

Nonetheless, given the number of proposals out there for improving Penn Station, including ReThinkNYC and Penn Design’s plan, it’s important to think of longer-term plans for better vertical circulation. When I proposed eliminating Penn Station’s above-ground infrastructure, I came up with a design for six approach tracks (including a new Hudson tunnel connecting to Grand Central), each splitting into two platform tracks facing the same platform; the six platforms would each be 15 meters wide, but unlike Les Halles, each of six access points would have six escalators, four up and two down in the morning peak, or alternatively four escalators and a wide staircase (the climb is 13 meters, equivalent to a five-floor walkup). There would be ample capacity for anything; emptying a full 12-car train would take forty seconds, and it’s unlikely an entire 12-car train would empty.

Neighborhoods With Excess Capacity

In New York, the tech industry has clustered in the Meatpacking District, around 14th Street and 8th Avenue. Google’s building (the company’s largest office outside the Googleplex) is there, Samsung’s New York offices are there, startup incubators are there with co-working spaces. Stephen Smith has called for commercial upzoning there (on YIMBY three years ago, and on Twitter just now), despite NIMBY objections. He argues not only that there is pent-up demand for office space, but also that there is excess subway capacity there: “the L train’s capacity west of Union Square is essentially unlimited, after the hordes from Brooklyn headed to destinations east of Broadway change for the 4/5/6 and N/Q/R.” While his other arguments for upzoning are solid, this one is incorrect, and I’d like to explain which areas have excess capacity and which don’t.

Two years ago, I wrote this post about modeling transit crowding. The model is primitive – it assumes a one-dimensional city, 100% mode share, and independent job and residence distributions. For the purposes of this post, cities A, B, and C from the model are not relevant (they have perfect mixture of jobs and residences); cities D, E, and F, with separation of residences and jobs, are more relevant, with city F, with partial mixture, the most useful.

The results of the model are fairly predictable. In the morning peak, transit vehicles (or roads!) fill up toward the center as they pass through residential areas, and then empty in the commercial core. This means that more residences outward of the point of greatest congestion, and more jobs inward of it, add more crowding; more jobs outward of the point, and more residences inward of it, do not. More jobs on the other side of city center add to crowding, because people still ride through the point of greatest crowding.

On the L, the point of greatest crowding is between Bedford Avenue (the last stop in Brooklyn) and First Avenue (the first in Manhattan). This means that more residential development on the L in Brooklyn and more commercial development in Manhattan would add crowding – even commercial development on the West Side would attract riders living in Brooklyn, who would ride through the overcrowded segment under the East River. The other subway lines serving the Meatpacking District suffer from the same problem: those are the 2 and 3 at 7th Avenue and 14th Street, and the A, C, and E at 8th Avenue. With Second Avenue Subway having taken some crowds off the 4 and 5 on the East Side, it’s likely the 2, 3, and E are the most crowded subway lines in New York today (the A has more room). Yes, most riders on those lines get off in Midtown, but it doesn’t matter, because riders from the Upper West Side and Queens, attracted to new jobs in the Meatpacking District, would still ride through the most crowded point, at the entry to Midtown.

So if not the Meatpacking District, where is it better to add jobs, purely from the perspective of subway crowding? Superficially, the answer is to mix them across the residential parts of the city. But here, my model runs into problems with mode share. The model says that adding jobs in (say) Downtown Brooklyn increases subway crowding, because of riders from Uptown Manhattan riding to the south. Per the model, it’s best to add jobs on the side with more crowding, which is the north and Queens sectors, not the Brooklyn sector, where only the L is very crowded. This means, more jobs on the Upper East and West Sides, and maybe also in Long Island City, near Queensboro Plaza.

But in reality, there is some travel segmentation in New York. People who work on the Upper East and West Sides probably live in those neighborhoods or in Harlem and the Bronx, and people who work in Downtown Brooklyn probably live elsewhere in Brooklyn. Yes, it’s possible to commute between the Upper East Side and Downtown Brooklyn, but people would not ordinarily choose to do so – the commute is long and crowded (because of all the Midtown-bound workers), and there isn’t much saving on rent. People might still do it for various reasons, like a two-body problem or moving frequently between jobs – this is why through-running is important – but it’s much less common than living and working on the same side of city center.

So most likely, office development in Downtown Brooklyn would mainly attract ridership from within Brooklyn. Extra ridership from Uptown Manhattan and the Bronx is likely to be small. The upshot is that locations outside the most crowded point on each inbound subway line are likely to lead to large gains in subway ridership without much additional crowding.

I bring up Downtown Brooklyn and not just the Upper West and East Sides because it is better-connected to more bedroom communities by subway. These include the Lower East Side and Chinatown, Long Island City, and nearly all of Brooklyn. Long Island City is also highly accessible, from much of Queens and the parts of Brooklyn on the G train. But the Upper West and East Sides aren’t so accessible because of the lack of good east-west subway options.

Of course, the situation on the ground is different. New York is desperate to add tech jobs in Downtown Brooklyn, but the tech industry insists on clustering in the Meatpacking District. There’s only so much a city can force developers to site themselves in the areas most convenient for infrastructure. But from a long-term capacity standpoint, it’s in New York’s interest to encourage commercial development outside the Manhattan core, especially in areas that get decent subway service from multiple directions, like Long Island City, Downtown Brooklyn, and maybe Jamaica.

It would be easier if there were more service targeted at off-core destinations. This is part of why I harp on regional rail all the time – the LIRR would be able to serve Downtown Brooklyn and Jamaica better if it didn’t exist just for the benefit of suburban salarymen working in Midtown. But this also includes Triboro, which would give multidirectional service to nodes including Jackson Heights, the Bronx Hub, and Brooklyn College. This would encourage developers to build commercial at these nodes, which suffer from poor access to workers today.

Note that opening circumferential transit, in this model, has the opposite of the expected effect on radial lines. Normally, a new transit line reduces demand on parallel lines and increases demand on intersecting lines, which runs the risk of overloading them. But if a circumferential line encourages office development at intersection points with radials, it will still encourage more ridership on the radials, but this ridership will completely miss the congested inner portions of the radials.

Suspended Railways

Suspended railways are not a common mode of transportation. In Europe, the best-known example is the Wuppertal Suspension Railway, opened in 1901. Two examples exist in Japan, which is more willing to experiment with nonstandard rail technology. With essentially just these three examples in normal urban rail usage, it is hard to make generalizations. But I believe that the technology is underrated, and more cities should be considering using it in lieu of more conventional elevated or underground trains.

The reason why suspended trains are better than conventional ones is simple: centrifugal force. Train cars are not perfectly rigid – they have a suspension system, which tolerates some angle between the bogies and the carbody. Under the influence of centrifugal force, the body leans a few degrees to the outside of each curve:

 

If the train is moving away from you, and is turning left, then the outside of the curve is to your right; this is where the body leans in the image on the right. This is because centrifugal force pushes everything to the right, including in particular the carbody. This increases the centrifugal force felt by the passengers – the opposite of what a tilt system does. A train is said to have soft suspension if this degree of lean is large, and rigid suspension if it is small. The depicted image is rotated 3 degrees, which turns 1 m/s^2 acceleration in the plane of the tracks into 1.5 m/s^2 felt by the passengers; this is the FRA’s current limit, and is close to the maximum value of emergency deceleration. There are no trains with perfectly rigid suspension, but the most recent Shinkansen trains have active suspension, which provides the equivalent of 1-2 degrees of tilt.

On a straddling train, this works in reverse. A straddling train moving away from you turning left will also suspend to the right:

 

It’s almost identical, except that now the floor of the train leans toward the inside of the curve, rather than to the outside. So the suspension system reduces the lateral acceleration felt by the passengers, rather than increasing it. By softening the suspension system, it’s possible to provide an arbitrarily large degree of tilt, limited only by the maximum track safety value of lateral acceleration, which is not the limiting factor in urban rail.

This is especially useful in urban rail. Longer-distance railroads can superelevate the tracks, especially high-speed tracks, where trains have to be reliable enough for other reasons that they never have to stop in the middle of a superelevated curve. Some urban rail lines have superelevation as well, but not all do. Urban rail lines with high crowding levels routinely stop the trains in the middle of the track to maintain sufficient spacing to the train ahead; this is familiar to my New York readers as “we are being delayed because of train traffic ahead of us,” but the same routinely happens in Paris on the RER. This makes high superelevation dicey: a stopped train leans to the inside of the curve, which is especially uncomfortable for passengers. High superelevation on urban rail is also limited by the twist, i.e. the rate at which the superelevation increases per linear meter (in contrast, on intercity rail, the limiting factor is jerk, expressed in superelevation per second).

Another reason why reducing curve radius is especially useful in urban rail is right-of-way constraints. It’s harder to build a curve of radius 200 meters in a dense city (permitting 60 km/h with light superelevation) than a curve of radius 3 km outside built-up areas (permitting 250 km/h with TGV superelevation and cant deficiency). Urban rail systems make compromises about right-of-way geometry, and even postwar systems have sharp curves by mainline rail standards; in 1969, the Journal of the London Underground Railway Society listed various European limits, including Stockholm at 200 meters. The oldest lines go well below that – Paris has a single 40-meter curve, and New York has several. Anything that permits urban rail to thread between buildings (if above ground), building foundations (if underground), and other lines without sacrificing speed is good; avoiding curves that impose 30 km/h speed limits is important for rapid transit in the long run.

Suspended railways are monorails, so they run elevated. This is not inherent to the technology. Monorails and other unconventional rail technologies can go underground. The reason they don’t is that a major selling point for monorails is that their sleek structures are less visually obtrusive when elevated. But underground they can still use the same technology – if anything, the difficulty of doing emergency evacuation on an elevated suspended monorail is mitigated on an underground line, where passengers can hop to the floor of the tunnel and walk.

I’d normally say something about construction costs. Unfortunately, the technology I am plugging has three lines in regular urban operation, opened in 1901, 1970, and 1988. The 1988 line, the Chiba Monorail, seems to have cost somewhat more per km than other contemporary elevated lines in Japan, but I don’t want to generalize from a single line. Underground there should not be a cost difference. And ultimately, cost may well be lower, since, at the same design speed, suspended monorails can round tighter curves than both conventional railroads and straddle monorails.

Despite its rarity, the technology holds promise in the most constrained urban environments. When they built their next new metro lines, disconnected from the older network, cities like New York, London, Paris, and Tokyo should consider using suspended railroads instead of conventional subways.