Radial Metro Networks for Portions of Cities

I’ve harped about the necessity of radial metro networks, looking much like the following schematic:

However, in practice such pure radial networks are rare. Some networks have parallel lines (such as Paris and Beijing), nearly all have lines intersecting without a transfer at least once (the largest that doesn’t is Mexico City), some have chordal lines and not just radial or circular lines, and nearly all have lines that meet twice. Often these variations from pure radii are the result of poor planning or a street network that makes a pure radial system infeasible, but there are specific situations in which it’s reasonable for lines to meet multiple times (or sometimes even be parallel). These come from the need to built an optimal network not just for the whole city but also notable portions of it.

The unsegmented city

The diagram depicted above is a city with a single center and no obvious sub-areas with large internal travel demand. If the city is on a river, it’s not obvious from the subway map where the river passes, and it’s unlikely its non-CBD bank has a strong identity like that of the Left Bank of Paris, South London, or Brooklyn and Queens.

Among the largest metro networks in the world, the one most akin to the diagram above is Moscow. It has seven radial lines through city center (numbered 1-10, omitting the one-sided 4, the circular 5, and the yet-incomplete 8). They have some missed connections between them (3/6, 3/7, 6/9), and one pair of near-parallel lines (2/10, meeting only at Line 10’s southern terminus), but no parallel lines, and no case in which two lines cross twice. And Moscow’s development is indeed oriented toward connecting outlying areas with city center. Connections between areas outside the center are supposed to use the circular lines (5 and 14, with 11 under construction).

In a relatively monocentric city, this is fine. Even if this city is on the river, which Moscow is, it doesn’t matter too much if two neighborhoods are on the same side of the river when planning the network. Even in polycentric cities, this is fine if the sub-centers get connections via circular lines or the odd chordal line (as will eventually happen when Los Angeles builds a real subway network with such chords as Vermont and Sepulveda).

The segmented city

London and Paris are both segmented by their rivers, and their wrong sides (South London, Left Bank) both have strong regional identities, as does to some extent East London. New York, partitioned into boroughs by much wider waterways than the Thames and Seine, has even stronger sub-identities, especially in Brooklyn. I do not know of a single New Yorker whose commute to work or school involves crossing a bridge over a river on foot, nor of any case of anyone crossing a bridge in New York on foot (or bike) except for recreational purposes; in Paris I do so habitually when visiting the Latin Quarter, and at a conference in 2010 another attendee biked from Porte de Vincennes to Jussieu every day.

With a difficult water boundary, the wrong-side part of the city became a center in its own right. Downtown Brooklyn and the Latin Quarter should both be viewed as sub-centers that failed to become CBDs. The Latin Quarter, the oldest part of Paris outside the Ile de la Cite, declined in favor of the more commercial Right Bank as the city grew in the High and Late Middle Ages; Downtown Brooklyn declined in favor of more concentration in Manhattan and more dispersion to other centers (often in Queens) over the course of the 20th century.

Early 20th century New York and Paris were not polycentric cities. There was no everywhere-to-everywhere demand. There was demand specifically for travel within Brooklyn and within the Left Bank. To this day, the connections to the Latin Quarter from Right Bank neighborhoods not on Line 4 are not great, and from Nation specifically the alternatives are a three-seat ride and a long interchange at Chatelet. Ultimately, this situation occurs when you have a region with a strong identity and strong demand for internal travel larger than a neighborhood (which can be served by a few subway stops on a single line) but smaller than an entire city.

In this case, a radial subway network (which neither the New York City Subway nor the Paris Metro is) could justifiably have multiple crossings between two lines, ensuring that lines provide a coherent network for internal travel. South London is a partial example of this principle: not counting the Wimbledon branch of the District line, the South London Underground network is internally connected, and the best route between any two South London stations stays within South London. In particular, the Victoria and Northern lines cross twice, once at Stockwell and once at Euston, in a city that has a generally radial metro system.

Don’t go overboard

The need to serve internal travel within portions of a city is real, and it’s worthwhile to plan metro networks accordingly. But at the same time, it’s easy to go overboard and plan lines that serve only travel within such portions. Most of the examples I give of weak chordal lines – the G train in New York, Line 10 and the RER C in Paris, Line 6 in Shanghai – serve internal demand to the wrong side of a city divided by a river; only Shanghai’s Line 3 is an exception to this pattern, as a weak chordal line that doesn’t come from city segmentation.

In the cases of the G and M10, the problem is partly that the lines have compromises weakening them as radials. The G has too many missed connections to radial lines, including the J/Z and the entire Atlantic-Pacific complex; M10 terminates at Austerlitz instead of extending east to the library, which is the second busiest Left Bank Metro stop (after Montparnasse) and which has a particularly strong connection to the universities in the Latin Quarter.

But Line 6 is constrained because it doesn’t serve Lujiazui, just Century Avenue, and the RER C does serve the library but has exceptionally poor connections to the CBD and other Right Bank destinations. It’s important to ensure the network is coherent enough to serve internal demand to a large segment of the city but also to serve travel demand to the rest of the city well.

Good transfers

Serving the entire city hinges on good transfers. The most important destination remains city center, so lines that aren’t circumferential should still aim to serve the center in nearly all cases. Internal demand should be served with strategic transfers, which may involve two lines crossing multiple times, once in or near city center and once on the wrong side of the river.

The main drawback of multiple crossings is that they are less efficient than a pure radial network with a single city center crossing between each pair of lines, provided the only distinguished part of the city is the center. Once internal travel to a geographic or demographic segment is taken into account, there are good reasons to slightly reduce the efficiency of the CBD-bound network if it drastically raises the efficiency of the secondary center-bound network. While demographic trends may come and go (will Flushing still be an unassimilated Chinese neighborhood in 50 years?), geographic constraints do not, and place identities like “Left Bank” and “Brooklyn” remain stable.

Note the qualifiers: since the CBD remains more important than any secondary center, it’s only acceptable to reduce CBD-bound efficiency if the gain in secondary center-bound efficiency is disproportionate. This is why I propose making sure there are good transfers within the particular portion of the city, even at the cost of making the radial network less perfect: this would still avoid missed connections, a far worse problem than having too many transfer points.

So what?

In New York, London, and Paris, the best that can be done is small tweaks. However, there exist smaller or less developed cities that can reshape their transit networks, and since cities tend to form on rivers and bays, segmentation is common. Boston has at least two distinguished wrong-side segments: East Boston (including Chelsea and Revere) and Greater Cambridge. East Boston can naturally funnel transit through Maverick, but in Greater Cambridge there will soon be two separate subway spines, the Red and Green Lines, and it would be worthwhile to drag a rail connection between them. This is why I support investing in rail on the Grand Junction, turning it into a low-radius circular regional rail line together with the North-South Rail Link: it would efficiently connect the Green Line Extension with Kendall.

More examples of segmented cities include the Bay Area (where the wrong-side segment is the East Bay), Istanbul (where Europe and Asia have separate metro networks, connected only by Marmaray), Stockholm (where Södermalm and Söderort are separated by a wide channel from the rest of the city, and Kungsholmen is also somewhat distinguished), and Washington (where the wrong side is Virginia). In all of these there are various compromises on metro network planning coming from the city segmentation. Stockholm’s solution – making both the Red and Green Lines serve Slussen – is by far the best, and the Bay Area could almost do the same if BART were connected slightly differently around Downtown Oakland. But in all cases, there are compromises.

Development-Oriented Transit, Redux

I wrote years ago about the problems of so-called development-oriented transit – that is, transit built not to serve current demand but future development, often to be funded via land value capture and other opaque mechanisms. Today I want to talk not so much about the transit itself but the arguments people make for it.

The context is that I appeared on Kojo Nnamdi’s show last week discussing the plans for a ferry network in Washington DC, which I had heavily criticized in an article for the DC Policy Center. I was discussing the issue with guest host Marc Fisher and two locals involved in the ferry plan. I criticized the ferry plan over the poor land use on most of the waterfront on both sides of the Potomac, contrasting it with the Staten Island Ferry and Vancouver’s SeaBus (both of which have skyscrapers going almost to the water’s edge at the CBD end and decent secondary CBD development at the outlying end). My interlocutors answered, don’t worry, the area is undergoing redevelopment.

I heard something similar out of Boston, regarding the Seaport. People recurrently talk on Commonwealth about how to connect to the Seaport better, and at one point there was a plan to have the Fairmount Line reverse-branch to serve the Seaport (rather than going into the CBD proper at South Station). The crayonistas talk about how to connect the Green Line to the Seaport. Whenever I point out that the Seaport is at best a tertiary destination I’m told that it’s growing so it needs some transit.

In both cases, what’s missing is scale. Yes, waterfront redevelopment in former industrial cities is real. But the only place where it’s happened on sufficient scale to merit changing the entire transit system to fit the new development is London, around Canary Wharf. And even in London, the CBDs are unambiguously still the City and the West End; Canary Wharf is a distant third, deserving of a Crossrail line and some Tube lines but not of the dense mesh of transit that the City and West End have.

The important thing to understand is that TOD sites are practically never going to eclipse the CBD. La Defense, for all its glass-clad glory, is still smaller than the Paris CBD, stretching from west of Les Halles to east of Etoile. The peak job density at La Defense is higher, but westbound RER A trains are at their most crowded heading into Auber, not La Defense, and the CBD maintains its medium-high job density for several square kilometers while La Defense is geographically small. And your city’s waterfront redevelopment is not going to be La Defense or Canary Wharf.

If the TOD sites are not going to be primary CBDs, then they must be treated as secondary centers at best. One does not build transit exclusively for a secondary center, because people along the lines that serve it are going to be much more interested in traveling to the primary CBD. For example, people at the origin end of a ferry system (in Washington’s case this is Alexandria and suburbs to its south) are traveling to the entirety of city center, and not just to the redevelopment site near the waterfront. Thus the transit that they need has to connect to the CBD proper, which in Washington’s case is around Farragut and Metro Center. A ferry system that doesn’t connect to Metro well is of no use to them, and whatever redevelopment Washington puts up near the Navy Yard won’t be enough to prop up ridership.

The principle for redeveloped waterfronts has to be the same as for every secondary neighborhood destination: be on the way. If there is cause to build an entirely new metro line, or run more buses, and the new service can plausibly go through the redevelopment site, then it should. In Boston’s case, the 7 bus has high usage for how short it is, and so does the Silver Line going to the airport, so it’s worthwhile making sure they run more efficiently (right now the 7 and Silver Line run along the same inner alignment but peak in opposite directions without being able to share infrastructure or equipment) to serve the Seaport better. However, building a line from scratch just for the Seaport is a bad idea, and the same is true of the area around Waterfront and the Navy Yard in Washington.

In fact, the two closest things New York has to Canary Wharf – the Jersey City waterfront and Long Island City – both developed precisely because they were on the way. PATH was built to connect the railroad terminals at the then-industrial waterfront and the traditional center of Jersey City at Journal Square with Manhattan. Mainline trains began to be diverted from Jersey City to Manhattan when Penn Station opened, and with the general decline of rail traffic the waterfront was abandoned; subsequently, Exchange Place and Pavonia/Newport became major job and retail centers, since they had available land right on top of rapid transit stations minutes from Lower Manhattan. In Queens, something similar happened with Long Island City, once a ferry terminal on the LIRR, now a neighborhood with rapid residential and commercial growth since it sits on multiple subway lines just outside Midtown.

One exception to the be on the way rule is if there is a nearby stub-end line or a natural branch point. Some metro lines stub-end in city center rather than running through, such as the Blue Line in Boston, the 7 and L trains in New York, and Metro Line 11 here in Paris. If they can be plausibly extended to a new redevelopment site, then this is fine – in this case the CBD will be on the way to the new site. The 7 extension is one example of this principle; the extension is overall not a success, but this is exclusively due to high costs, while ridership per km is not terrible.

In London, the Jubilee line and Crossrail are both examples of this exception around Canary Wharf. Crossrail expects intense demand into Central London but less demand on the specific eastern branch used (the Great Eastern slow lines), making the City into a natural branch point with a separate branch to Canary Wharf and Southeast London. And the Jubilee line stub-ended at Charing Cross when it first opened in the 1970s; plans for an extension to the east are even older than the initial line, and once Canary Wharf became a major office building site, the plans were changed so as to serve the new center on the way to Stratford (itself an urban renewal site with extensive redevelopment, it’s just smaller than Canary Wharf).

The ultimate guideline here is be realistic. You may be staring at a place that’s doubled its job density in a decade, but it won’t be able to double its density every decade forever, and most likely you’ll end up with either high-density condo towers or a small job cluster. This means that you should plan transit to this site accordingly: worth a detour on a line to the CBD, but not worth an entire system (whether ferry or rail) by itself.

Guidelines for Driverless Buses

As I’ve said a few months ago in The American Prospect, driverless bus technology does not yet appear ready for mass deployment. However, research into this technology continues. Of particular note is Google’s work at Waymo, which a source within the Bay Area’s artificial intelligence community tells me is more advanced and more serious than the flops at Uber and Tesla; Waymo’s current technology is pretty good on a well-understood closed route, but requires laborious mapping work to extend to new routes, making it especially interesting for fixed-route buses rather than cars. But ultimately, automated vehicles will almost certainly eventually be mature and safe, so it is useful to plan around them. For this, I propose the following dos and don’ts for cities and transit agencies.

Install dedicated, physically-separated bus lanes

A bus with 40 people should get 40 times the priority of a car with one person, so this guideline should be adopted today already. However, it’s especially important with AVs, because it reduces the friction between AV buses and regular cars, which is where the accident in Las Vegas reference in my TAP article happened. The CityMobil2 paradigm involves AVs in increasingly shared traffic, starting from fully enclosed circuits (like the first line in Helsinki, at the zoo) and building up gradually toward full lane sharing. Dedicated lanes are a lower level of sharing than mixed traffic, and physical separation reduces the ability of cars to cut ahead of the bus.

If there is a mixture of AV and manual buses, both should be allowed in the dedicated lanes. This is because bus drivers can be trained to know how to deal with AVs. Part of the problem with AVs in mixed traffic is that human drivers are used to getting certain cues from other human drivers, and then when facing robot drivers they don’t have these cues and misread the car’s intentions. But professional drivers can be trained better. Professional bus drivers are also familiar with their own bus system and will therefore know when the AV is going to turn, make stops, and so on.

Use Kassel curbs to provide wheelchair accessibility

Buses are at a disadvantage compared with trams in wheelchair accessibility. Buses sway too much to have the precise alignment that permits narrow enough gaps for barrier-free access on trains. However, as a solution, some German cities have reconstructed the edges of the bus lane next to the bus stop platform, in order to ease the wheels into a position supporting step-free access on low-floor buses. Potentially, AVs could make this easier by driving more precisely or by having platform extenders similar to those of some regional trains (such as those of Zurich) bridging the remainder of the horizontal gap.

Driverless trains in Vancouver and even on Paris Metro Line 14 have roll-on wheelchair access: passengers in wheelchairs can board the train unassisted. In contrast, older manually-driven trains tend to tolerate large horizontal and vertical gaps blocking passengers in wheelchairs, to the point that New York has to have some special boarding zones for wheelchairs even at accessible stations. If the combination of precision driving and Kassel curbs succeeds in creating the same accessibility on a bus as on SkyTrain in Vancouver, then the bus driver’s biggest role outside of actually driving the bus is no longer necessary, facilitating full automation.

Don’t outsource planning to tech firms

Transit networks work best when they work in tandem. This means full fare and schedule integration within and across different modes, and coordinated planning. Expertise in maintaining such networks lies within the transit agencies themselves as well as with various independent consultancies that specialize in transportation.

In contrast, tech firms have little expertise in this direction. They prefer competition to cooperation, so that there would be separate fleets within each city by company – and moreover, each company would have an incentive to arrange schedules so that buses would arrive just ahead of the other companies to poach passengers, so there wouldn’t be even headways. The culture of tech involves brazen indifference to domain expertise and a preference for reinventing the wheel, hence Uber and Chariot’s slow realization that no, really, fixed-route buses are the most efficient way of carrying passengers on the street in dense cities. Thus, outsourcing planning is likely to lead to both ruinous competition and retarded adoption of best practices. To prevent this, cities should ban private operations competing with their public bus networks and instead run their own AVs.

Most of the world’s richest cities have deep pools of tech workers, especially the single richest, San Francisco. It would be best for Muni, RATP, NYCT, and other rich-city agencies to hire tech talent using the same methods of the private sector, and train them in transit network planning so that they can assist in providing software services to the transit system in-house.

Resist the siren song of attendants

Las Vegas’s trial run involved an attendant on each bus performing customer service and helping passengers in wheelchairs. A bus that has an attendant is no more a driverless bus than a subway with computer-controlled driving and an operator opening and closing doors is a driverless train. The attendant’s work is similar to that of a bus driver. If the hope of some private operators is that relabeling the driver as an attendant will allow them to de-skill the work and hire low-pay, non-union employees, then it’s based on a misunderstanding of labor relations: transit employees are a prime target for unionization no matter whether they are called drivers.

Ultimately, the difficulty of driving a bus is not much greater than that of dealing with annoying customers, being on guard in case passengers act aggressively or antisocially, and operating wheelchair lifts. Bus drivers get back pain at high rates since they’re at the wheel of a large vehicle designed for passenger comfort for many hours a day, but this may still be a problem on AVs, and all other concerns of bus drivers (such as the risk of assault by customers) remain true for attendants. Either get everything right to the point of not needing any employee on the bus, or keep manual driving with just some computer assistance.

Resist the siren song of small vehicles

All AV bus experiments I know of (which I know for a fact is not all AV buses that are trialing) involve van-size vehicles. The idea is that, since about 75% of the cost of running a bus today is the driver’s wage, there’s no real point in running smaller vehicles at greater frequency if there’s a driver, but once the driver is removed, it’s easy enough to run small vehicles to match passenger demand and reduce fuel consumption.

However, vans have two problems. First, they only work on thin routes. Thick routes have demand for articulated buses running at high frequency, and then vans both add congestion to the bus lane and increase fuel consumption (when the vehicles are full, bigger is always more fuel-efficient). And second, they lead to safety problems, as passengers may be afraid of riding a bus alone with 3-4 other passengers but not with 20 or more (Martha Lauren rides full London buses fearlessly but would make sure to sit near the driver on nearly-empty Baltimore buses).

Medium-size buses, in the range of 20-30 seats, could be more useful on thin routes. However, passenger safety problems are likely to remain if only a handful of people ride each vehicle.

Get your maintenance costs under control

If you remove the driver, the dominant factor in bus operating costs becomes maintenance. Assuming maintenance workers make the same average annual wage and get the same benefits as transit workers in general, the wages of maintenance workers are about 15% of the total operating costs of buses in Chicago and 20% in New York.

The importance of fuel economy grows as well, but fuel today is a much smaller proportion of costs. Around 3% in Chicago and 2% in New York. European fuel costs are much higher than Americans, but so are European bus fuel economy rates: in tests, Boris buses got 4.1 km per liter of diesel, which is maybe twice as good as the US average and three times as good as the New York average.

This suggests that with the driver gone, maybe 75% of the remaining variable operating cost is maintenance. Chicago does better than New York here, since it replaces 1/12 of its fleet every year, so every year 1/12 of the fleet undergoes mid-life refurbishment and work is consistent from year to year, whereas in New York the replacement schedule is haphazard and there is more variation in work needs and thus more idle time. The most important future need for AV procurement is not electric traction or small size, but low lifecycle costs.

Update: by the same token, it’s important to keep a lid on vehicle procurement costs. New York spends $500,000 on a standard-length bus and $750,000 on an articulated bus; the Boris buses, which are bilevel and similar in capacity to an artic, cost about $500,000, which is locally considered high, and conventional artic or bilevel buses in London cost $300,000-350,000. American cities replace buses every 12 years, compared with every 15 years in Canada, and the depreciation in New York is around 6% of total bus operating costs. Cutting bus procurement costs to London levels would only save New York a small percent of its cost, but in an AV future the saving would represent around 12% of variable costs.

Plan for higher frequency

AVs represent an opportunity to reduce marginal operating costs. This means transit agencies should plan accordingly:

  • Lower marginal costs encourage running buses more intensively, running almost as much service off-peak and on weekends as at rush hour.
  • Very high frequency encourages passengers to transfer more, so the value of one-seat rides decreases.
  • Higher frequency always increases capacity, but its value to passengers in terms of reduced wait times is higher when the starting frequency is low, which means agencies should plan on running more service on less frequent routes and only add service on routes that already run every 5 minutes or less if the buses are overcrowded.

The Role of Local Expertise in Construction Costs

When I first looked at construction costs, I looked exclusively at developed countries. Eventually I realized that the difference in average costs between rich and poor countries is small. But then I noticed a different pattern in the third world: some places, like India, Bangladesh, Nigeria, and Indonesia, spend much more than China does. Why is that? While I’ve had a bunch of different explanations over the years, I believe today that the difference concerns local expertise versus reliance on first-world consultants.

The facts, as far as I can tell, are as follows:

  • Construction costs in China are about $250 million per km, a little more than the average for Continental Europe.
  • Construction costs in post-communist Europe are all over, but are the same range as in Western Europe. Bulgaria is pretty cheap; in this post I bring up a line that costs around $200 million/km in today’s money but other extensions built this decade are cheaper, including one outer one at $50 million/km. In contrast, Warsaw’s Line 2 is quite expensive.
  • Latin American construction costs have the same range as Europe, but it seems more compressed – I can’t find either $50 million/km lines or $500 million/km ones.
  • Africa and the parts of Asia that used to be colonies have high construction costs: India and Egypt are expensive, and here I give two expensive examples from Bangladesh and Indonesia. The Lagos Metro is spending subway money on an el in the middle of a wide road and is reminiscent of American costs.
  • When the first world had comparable income levels to those of the third world today, in the early 20th century, its construction costs were far lower, around $30-50 million per underground km. First-world cost growth in the last 100 years has mostly tracked income growth – it’s been somewhat faster in New York and somewhat slower in Paris, but on average it’s been similar.

For a while, I had to contend with the possibility that Chinese autocracy is just better at infrastructure than Indian (or Bangladeshi, or Indonesian, or Nigerian) democracy. The nepotism and corruption in India are globally infamous, and it’s still well-governed compared with Indonesia and Nigeria, which have personality-based politics. But then, in the developed world, authoritarian states aren’t more efficient at construction (Singapore’s construction costs are high); moreover, post-communist democracies like Bulgaria and Romania manage low construction costs.

What I instead think the issue is is where the state’s infrastructure planning comes from. China learned from the USSR and subsequently added a lot of domestic content (such as the use of cut-and-cover in some situations) fitting its particular needs; as a result, its construction costs are reasonable. The post-communist world learned from the USSR in general. There’s a wide range, with Romania near one end and Poland near the other, but the range is comparable to that of Western Europe today. Overall it seems that Eastern Europe can competently execute methods geared to the middle-income world (as the second world was in the Cold War) as well as, thanks to assistance from the EU, the high-income world.

Latin America, too, uses domestically-developed methods. The entire region is infamous in the economic development literature for having begun an inward economic turn in the Great Depression, cutting itself off from global markets and generally stagnating. Government functions are likewise done domestically or maybe outsourced to domestic contractors (and if international ones are involved, it’s in construction, not planning). Evidently, Latin America developed bus rapid transit, a mode of transportation optimally designed for countries with low incomes (so paying armies of bus drivers is cheaper than building rail tracks) and relatively strong currencies (so importing buses from richer countries isn’t ruinously expensive).

The situation in the ex-colonies is completely different. Even relatively protectionist ones outsource much of their planning to the developed world or increasingly to China, out of a combination of cultural cringe and shortage of domestic capital. The metro lines I have data for in India, Bangladesh, and Indonesia all involve Japanese technology and planning, with no attempt to adapt the technology to local conditions. So insistent is Japan on following its domestic recipe exactly that India’s high-speed rail construction is using standard gauge rather than broad gauge and Shinaknsen-size trains rather than larger Indian trains (which are 3.7 meters wide and can fit people 6-abreast). Elsewhere, China contributes capital and planning as part of the Belt and Road Initiative, and then its methods are geared toward middle income and not low income.

The correct way for countries in the per capita income range of Nigeria, India, and Bangladesh to build subways is to open up their main roads, which are often very wide, and put in four tracks in a cut-and-cover scheme similar to that of early-20th century New York. If they can elevate the tracks instead, they should use the same methods used to build Lines 2 and 6 in Paris in the early 20th century, which use concrete columns and are quiet enough that, unlike in New York, people can carry a conversation under the viaduct while a train passes. If the line needs to deviate from roads, then the city should buy property and carve up a new street (as New York did with Seventh Avenue South and Sixth Avenue in the Village) or else learn to implement late Victorian and Edwardian London’s techniques of deep boring.

However, actually implementing Belle Epoque construction methods requires particular knowledge that international consultants don’t have. Most of these consultants’ income comes from the first world, where wages are so high that the optimal construction methods involve extensive automation, using machinery rather than battalions of navvies with shovels. The technical support required for a tunnel boring machine is relatively easy in a rich country with a deep pool of qualified engineers and mechanics and a nightmare in a poor one where all such expertise has to be imported or trained from scratch. Thus, the consultants are likely to recommend the first-world methods they are familiar with, and if they do try to adapt to low wages, they may make mistakes since they have to reinvent ideas or read historical sources (which they are typically not trained to do – they’re consultants, not historians).

The result is that even though open economies tend to grow faster overall, economies with a history of closure tend to do better on this specific topic, where international consultants are not very useful for the needs of the developing world. India in particular needs to get better at indigenizing its construction and avoid mindlessly copying the first world out of cultural cringe, because even though it is almost a middle-income country by now, its wages remain a fraction of those of North America, Western Europe, and Japan, and its future growth trajectory is very different, requiring extensive adaptations. Both the overall extent of planning and the specific construction methods must be tailored to local conditions, and so far India seems bad at both (hence the undersized, expensive high-speed trains).

The Formula for Frequent Transit Networks

As I’m working on refining a concrete map for Brooklyn buses, I’m implementing the following formula:

Daily service hours * average speed per hour = daily frequencies * network length

In this post I’m going to go over what this formula really means and where it is relevant.

Operating costs

The left-hand side represents costs. The operating costs of buses are proportional to time, not distance. A few independent American industry sources state that about 75-80% of the cost of bus service is the driver’s wage; these include Jarrett Walker as well as a look at the payrolls in Chicago. The remaining costs are fuel, which in a congested city tracks time more than distance (because if buses run slow it’s because of stop-and-go traffic and idling at stops or red lights), and maintenance, which tracks a combination of time and distance because acceleration and braking cycles stress the engine.

This means that the number of service hours is fixed as part of the budget. My understanding is that the number in Brooklyn is 10,000 per weekday. I have seen five different sources about bus speeds and service provision in New York (or Brooklyn) and each disagrees with the others; the range of hours is between 9,500 and 12,500 depending on source, and the range of average speeds is between 9.7 km/h (imputed from the NTD and TransitCenter’s API) and 11 km/h (taken from schedules). The speed and hours figures are not inversely correlated, so some sources believe there are more service-km than others.

On a rail network, the same formula applies but the left-hand side should directly include service-kilometers, since rail operating costs (such as maintenance and energy) are much more distance- than time-dependent; only the driver’s wage is time-dependent, and the driver’s wage is a small share of the variable costs of rail operations.

Creating more service

Note that on a bus network, the implication of the formula is that higher speed is equivalent to more service-hours. My current belief, based on the higher numbers taken from schedules, is that 14 km/h is a realistic average speed for a reformed bus network: it’s somewhat lower than the average scheduled speed of the B44 SBS and somewhat higher than that of the B46 SBS, and overall the network should have somewhat denser stop spacing than SBS but also higher-quality bus lanes canceling out with it. The problem is that it’s not clear that SBS actually averages 14 km/h; my other sources for these two routes are in the 12-13 km/h range, and I don’t yet know what is correct. This is on top of the fact that faster transit attracts more paying riders.

Another way to create more service is to reduce deadheading and turnaround times. This is difficult. Bus depots are not sited based on optimal service. They are land-intensive and polluting and end up in the geographic and socioeconomic fringes of the city. The largest bus depot in New York (named after TWU founder Mike Quill) is in Hudson Yards, but predates the redevelopment of the area. In Brooklyn the largest depots appear to be East New York (more or less the poorest neighborhood in the city) and Jackie Gleason (sandwiched between a subway railyard and a cemetery). Figuring out how to route the buses in a way that lets them begin or end near a depot so as to reduce deadheading is not an easy task, but can squeeze more revenue-hours out of an operating cost formula that is really about total hours including turnaround time and non-revenue moves.

Service provision

The right-hand side of the equation describes how much service is provided. The network length is just the combined length of all routes. Daily frequency is measured in the average number of trips per day, which is not an easily understandable metric, so it’s better to convert it to actual frequencies:

Frequency Daily trips
15 minutes 6 am-9 pm, 30 minutes otherwise 5-1 am 70
15 minutes 24/7 96
5 minutes 7-9 am, 5-7 pm, 10 minutes otherwise 6 am-10 pm, 30 minutes 10 pm-12 am 124
5 minutes 7-9 am, 5-7 pm, 7.5 minutes otherwise 6 am-10 pm, 15 minutes 10 pm-12 am, 30 minutes overnight 164
6 minutes 6 am-10 pm, 10 minutes otherwise 5-12 am, 30 minutes overnight 188
5 minutes 6 am-10 pm, 10 minutes otherwise 5-12 am, 20 minutes overnight 228
3 minutes 7-9 am, 5-7 pm, 5 minutes otherwise 6 am-10 pm, 10 minutes otherwise 5-12 am, 20 minutes overnight 260

Daily trips are given per direction; for trips in both directions, multiply by 2. There are internal tradeoffs to each number of daily trips between peak and off-peak frequency and between midday frequency and span. But for the most part the tradeoff is between the average number of daily trips per route and the total route-length. This is the quantitative version of Jarrett’s frequency-coverage tradeoff. In reality it’s somewhat more complicated – for example, average speeds are lower at the peak than off-peak and lower in the CBD than outside the CBD, so in practice adding more crosstown routes with high off-peak frequency costs less than providing the same number of revenue-km on peaky CBD-bound buses.

It’s also important to understand that this calculation only really works for frequent transit, defined to be such that the ratio of the turnaround time to the frequency and length of each route is small. On low-frequency routes, or routes that are so short that their total length is a small multiple of the headway, the analysis must be discrete rather than continuous, aiming to get the one-way trip time plus turnaround time (including schedule padding) to be an even multiple of the headway, to avoid wasting time. On regional rail, which often has trains coming every half hour on outer tails and which is much more precisely scheduled than a street bus ever could be, it’s better to instead get the length of every route from the pulse point to the outer end to be an integer or half-integer multiple of the clockface headway minus the turnaround time.

Where is New York?

All of my numbers for New York so far should be viewed as true up to a fudge factor of 10-15% in each direction, as  my source datasets disagree. But right now, Brooklyn has about 10,500 revenue-hours per weekday (slightly more on a school day, slightly fewer on a non-school day) and an average speed of about 10.5 km/h, for a total of 110,000 revenue-km. Its bus network is 550 km long, counting local and limited versions of the same bus route as a single route but counting two bus routes that interline (such as the B67 and B69) separately; interlining is uncommon in Brooklyn, and removing it only shortens the network by a few km. This means that the average bus gets 200 runs per day, or 100 per direction.

Based on the above table, 100 runs per direction implies a frequency somewhat worse than every 5 minutes peak and every 10 off-peak. This indeed appears to be the case – nearly half of Brooklyn’s network by length has off-peak weekday frequency between 10 and 15 minutes, and the median is 12. At the peak, the median frequency, again by route-length, is 7 minutes. 7 minutes peak, 12 off-peak with some extra evening and night service works out to just less than 100 runs a day in each direction.

This exercise demonstrates the need to both shrink the network via rationalization to reduce the number of route-km and increase speed to raise the left-hand side of the equation. SBS treatments increased the speed on the B44 and B46 by 30-40% relative to the locals (not the limiteds), but just keeping the network as is would onl permit 130-140 buses per weekday per direction, which is more frequency but not a lot of frequency. The 7.5-minute standard that appears to be used in Toronto and Vancouver requires more; Barcelona’s range of 3-8 minutes implies an average of 5-6 and requires even more.

Where could New York be?

It’s definitely possible to get the number of daily frequencies on the average Brooklyn bus route to more than 200 in each direction. In Manhattan this appears true as well (the big question is whether the avenues can get two-way service), and in the Bronx 250 is easy. But even 200 in Brooklyn (which implies perhaps 350 km of network) requires some nontrivial choices about which routes get buses and which don’t, cutting some buses that are too close to other routes or to the subway. I’m not committing to anything yet because the margin calls happen entirely within the 10-15% fudge factor in my datasets.

The main reason I post this now is that I believe the formula is of general interest. In any city that wants to rationalize its transit system (bus or rail), the formula is a useful construction for the tradeoffs involved in transit provision. You can look at the formula and understand why some systems choose to branch: at the same average frequency the busiest parts of the network would get more service. You can also understand why some systems choose not to branch: at some ranges of frequency, the outer ends would get so little frequency that it would discourage ridership.

What is high frequency?

I’m using 5-6 minutes as a placeholder value beyond which there’s no point in raising frequency if there’s no capacity crunch. This isn’t quite true – on a 15-minute bus trip, going from 6 minutes between buses to 3 is a 14% cut in worst-case trip time including wait – but at this point higher frequency is at best a second-order factor. It’s not like now, when going from 15 minutes to 6 would reduce the worst-case trip time on the same bus trip by 30%.

The actual values depend on trip length. An intercontinental flight every hour is frequent; a regional train every hour is infrequent; a city bus every hour might as well not exist. One fortunate consequence is that bus trips tend to be shorter in precisely the cities that can most afford to run intensive service: dense cities with large rail networks for the buses to feed. New York’s average NYCT bus trip (excluding express buses) is 3.5 km; Chicago’s is 4.1 km; Los Angeles’s is 6.7 km. Los Angeles can’t afford to run 6-minute service on its grid routes, but trips are long enough that 10-minute service may be good enough to start attracting riders who are not too poor to own a car.

How YIMBY Reflects New York’s Priorities

The conversation about YIMBY and zoning seems to be centered around San Francisco. Googling YIMBY Guardian gives me two articles about Northern California out of the top three results (the third is an op-ed about London). But the real origin of YIMBY is New York. The term started with New York YIMBY, which was always a real estate magazine rather than an activist movement. San Francisco YIMBY adopted it and intended to publish under the umbrella of New York YIMBY before eventually going its own way, buoyed by SF YIMBY founder Sonja Trauss’s strong political organizing skills, which are much better than those of the New York YIMBY founder. However, for the most part the goals and actions of YIMBY are still based on New York-centric assumptions, which may not apply elsewhere.

This does not mean that YIMBY is a New York imposition. On the contrary. But some of the specific details come from New York’s context. They port more easily to Paris, Tokyo, and London than to San Francisco, Boston, and other American cities.

Commercial versus residential upzoning

I’ve argued for commercialization before. Near-CBD residential neighborhoods are prime locations for high-end retail and office uses, leading to expansion or even migration of the CBD. Midtown historically arose this way, beginning with commercialization around Fifth Avenue, and so did the Paris CBD, which is well to the west of the historic core; in London the primary CBD is still the City, but the West End has many jobs as well.

However, in practice, New York needs residential development more than commercial development. There is demand for new office space, particularly from the tech industry, but this is a minority of the city’s employment. In contrast, residential rents are very high, and there is very little construction permitted; according to data from the Department of Housing and Urban Development, the average over the last few years has been about 2.5 annual units permitted per 1,000 residents (in Tokyo the average is 10.7). As a result, New York’s activist YIMBY group, called Open New York, focuses on residential and mixed projects and not on purely commercial ones.

When a city does not allow the construction of office space in or near its center, jobs are displaced to sprawling suburbs. This is routine all over the US, where high-rise CBDs are surrounded immediately by residential neighborhoods with little political will for commercialization, and thus people work either in the CBD or in auto-centric suburban office parks. San Francisco is especially prone to this trend, since the origin of the tech industry is not in the city but in the office parks stretching from Redwood City to San Jose. If Uber, Airbnb, Slack, and Twitter don’t have room to grow in SoMa they will move to a suburb hungry for sales tax revenues. Nonetheless, SF YIMBY has opposed the plan to add office space to SoMa on the grounds that residential space is of prime importance.

The politics of rent stabilization

New York has rent control (which means the real rent is fixed) on a small number of apartments, all continuously occupied since 1971, mostly in rich Manhattan neighborhoods. It has wider rent stabilization in a large (though not overwhelming) fraction of rental units, which permits some real rent increases, determined politically every year but averaging about 1%. This status quo has many problems, chief of which is that the details of rent stabilization incentivize harassing tenants into leaving or looking for tenants who’d only stay for a short period of time. However, the status quo is politically stable.

The importance of this is that YIMBYs in New York don’t have to take a position on rent stabilization, or on related issues like inclusionary zoning (moreover, New York’s high real estate profits ensure that inclusionary zoning, which is a tax on revenue, has less impact than in cheaper cities like Portland, where the same tax on revenue represents a much higher tax on profits). SF YIMBY adopts this approach, but this comes into tension with California’s politics in which populists demand more rent control, even applying it to new buildings.

YIMBYs can’t honestly support rent control on new buildings and expect the private sector to keep providing housing. In New York it’s irrelevant because nobody calls for such policy, but San Francisco has a more active leftier-than-thou community (as does Paris, but this is expressed in museum exhibits about Che Guevara and not in rent control on new buildings).

The frontier of the Millennial middle class

When the middle class moves into a low-income area it’s called gentrification. However, the same trend can be observed in areas that are already well-off, including the neighborhood I grew up in, Tel Aviv’s Old North. The Old North was never poor: it was built in the 1930s and early 40s and the initial population was middle-class German immigrants fleeing Hitler. Nonetheless, by the 1980s the area was unfashionable, and the retail on the main commercial drag, Dizengoff Street, declined in favor of newer shopping malls. But since the late 1990s, younger people have moved in, making the area more in vogue, often renovating old buildings from the 1930s (which are a UNESCO heritage site, even though locally they’re viewed as dinghy). The demographic entering the neighborhood is the same as the one that gentrifies poorer neighborhoods (such as Florentin), so it’s worthwhile to view this as part of the same trend.

I bring this up because in New York this trend of a middle-class frontier includes a wide swath of neighborhoods, some poor and gentrifying (Harlem, Washington Heights, Bushwick, Lower East Side) but others already comfortable (Astoria, Upper West Side, Morningside Heights, South Brooklyn). Open New York has a policy of focusing on supporting construction in areas that are already rich and gentrified, to avoid the risk of gentrification in places like Washington Heights. As a strategy, it makes sense for New York, as well as for other city whose frontier of young middle-class urban transplants is mostly in well-off areas, like Chicago, Boston, and Paris. It’s weaker in San Francisco specifically, since there the frontier is largely the Mission, where gentrification is unavoidable.

The role of the suburbs

New York may be permitting only 2.5 housing units per 1,000 residents every year, but its in-state suburbs build even less. Westchester’s average between 2011 and 2017 is 0.9, Nassau County’s is 0.7, and Suffolk County’s is 0.8. Moreover, the dynamic of suburban white flight is well-understood around the region, and criticizing suburban-style exclusionary zoning is easy from within the city. There is animosity between the city and the suburbs, a feature shared with many areas in the American Rust Belt, and this makes it easier to demand more building in the city. (In the other direction, it’s easier to demand more construction in the city if there are no city-suburb social tensions at all.)

In the American Sunbelt, the situation is different. There is less city-suburb animosity – often the boundaries of the city include de facto suburban areas while excluding dense areas. (This is to some extent true of New York but the examples are all on the New Jersey side, which New Yorkers ignore.) Just saying “we need more housing” doesn’t sound progressive. What’s more, even in places like Houston and Austin, the city proper votes liberal and wants internal political movements to align on the left, let alone in California; in these areas, upzoning sounds like a bad deregulation.

Counterexample: single-family zoning

In exactly one respect, YIMBY groups in North America have proposed something that departs from the movement’s New York origins: they call for replacing single-family zoning with what they call missing middle, such as townhouses with two to four apartments per building. Missing middle is in turn relevant mostly to Canada, where there are mid- and high-rise neighborhoods and single-family neighborhoods and not much in between. In the US, everything is missing except single-family and CBD high-rises.

In New York, of course, there is no missing middle – for one, there are rowhouses, which would count as missing middle elsewhere. But more to the point, these rowhouses and townhouses are on the outer margins of the subway’s coverage area (such as Southern Brooklyn) or even beyond it (such as Kew Gardens Hills), and aren’t where there is the most demand. The demand is for converting surviving low-rise buildings in inner neighborhoods to mid- and high-rise apartment buildings, so this is what Open New York and urbanists in general focus on.

Which cities are like New York when it comes to YIMBY?

New York’s situation is the same as in the European cities I’m familiar with. Missing middle density in Paris happens on the outer branches of the RER network, whereas the real demand is for more housing in the city and a handful of rich inner suburbs in Hauts-de-Seine, and the same is true in Stockholm, London, Zurich, and other expensive European cities, even though they’re less dense than Paris so they might have rowhouses (like London) or missing middle density that needs to be replaced with mid-rise (like Zurich).

The politics in New York, where it’s easier to sidestep concerns about gentrification by just focusing on upzoning rich areas, is also similar to that of cities that never experienced white flight. This includes nearly all major cities in the developed world outside the US; the biggest exception I know of is Brussels, where the politics is complicated by the fact that middle-class residents are often affiliated with the EU and many only stay temporarily.

Commercialization of near-CBD areas is also more common in Europe, so there is less need to argue about that specifically. Zoning is also looser in the sense of permitting small offices, such as those of doctors, lawyers, and accountants, in residential zones. Thus the focus is exclusively housing, especially in the largest cities, i.e. London and Paris, where traffic congestion is such that there is less risk of job sprawl than in (say) Stockholm.

Finally, London and Paris have no rent control. Both have political controversies around this – Paris passed rent control but it was stricken down by the courts on administrative grounds, and in London some people are calling for rent control – but the current status quo is market-rate. The European cities I’m familiar with that have rent control do not have vacancy decontrol, unlike in the US, but instead have long waitlists, measured in years and in some extreme Stockholm examples even decades, so YIMBYs can more readily point to long waitlists as evidence that more housing construction is needed.

New York’s specific social issues are much more American than European, but the way they interact with its urban layout and transportation network is unique, partly because it has decent public transit unlike anywhere else in North America and partly because it’s just bigger. This interaction in turn makes its housing politics look somewhat more European as far as YIMBY is concerned. This suggests that people interested in making housing affordable should be especially excited to implement the proposed program in big global first-world cities outside New York, led by London and Paris (and Tokyo, which is already sufficiently YIMBY).

Here and in London, the need for more housing is dire, as in New York. What’s more, it’s not possible to just propose missing middle density in single-family areas or even mid-rises like California’s SB 827 and say something about great cities, because Paris is already great. (In London this is easier – there are rowhouses in zone 2 of the Underground.) There are some unusually short buildings here and there, down to 3-4 floors, but usually replacements have to be much bigger, so they’d be perhaps 12-15 floors. And in the most desirable neighborhoods, around the 8th and 16th, full high-rises are warranted. The one point of light is that such a program is unlikely to run into California’s gentrification concerns, if only because the main target areas for upzoning are the richest city neighborhoods in France.

I Saw a Stampede on the Metro

France won the World Cup. Once the final ended, people all over Paris went out to the streets to celebrate. At Nation I saw impromptu dancing, drivers waving tricolore flags, and car passengers climbing out of their cars to wave their own flags. But the real celebration was elsewhere, on Champs-Elysees in the central business district. This was well covered in the media; the Guardian cites an estimate of one million people going to Champs-Elysees to celebrate, and ESPN reports riots (which I didn’t witness but can easily believe happened given the general conduct I did see) and 110,000 police and gendarmerie officers.

The sidewalks were crowded and it was difficult to move; there were too few street closures, so pedestrians were confined to narrow zones for the most part. But the crowding was worst at the Metro stations, and RATP should learn from this example and do better next time there are large celebrations, perhaps next Bastille Day.

The problem is cascading closures. In London, where the Underground platforms are narrower and have fewer cross-passageways than the Metro platforms here, closures are routine at Bank because often the passageways get dangerously overcrowded. These closures cascade: once Bank is closed to limit crowding, passengers swarm the adjacent stations, such as Moorgate and London Bridge, which are not built to handle the typical Bank crowds, forcing TfL to close them as well.

France won the game around 7 in the evening Paris time. By 8, some stations on Champs-Elysees were closed, and as I sat on my severely delayed Metro Line 1 train, with passengers banging on the train’s walls and ceiling, I heard that they were closing more, ultimately going express from Palais-Royal to Argentine and skipping all the CBD stations, including Etoile. I got off at Argentine, as did practically the entire train. Not designed to handle the crowds of the entire CBD at once, Argentine’s platform was jammed. I spent maybe ten minutes trying to make my way from where I got off to the front end of the platform, where the only exits were, and failed, and at a few points the mass of passengers was such that I thought a stampede was likely. The only reason nobody fell onto the tracks was the platform edge doors, installed during the automation of Line 1.

Trains kept serving the station, dumping more and more people. The only mechanism preventing more passengers from getting on was that the crowding was so intolerable that some people started getting back onto the trains, including eventually me. I couldn’t even get off at the next stop, Porte Maillot – the platform was fine but the train was too crowded – so I got off in the suburbs, at Les Sablons, and walked back east.

Perhaps RATP did eventually close Argentine. But both RATP and the city made crucial mistakes that evening, which they should fix in the future.

First, they should have made the trains free to improve passenger circulation. Paying at the turnstiles takes time. This is especially bad in Paris, where there are separate gates for entry (which are turnstiles) and exit (which are one-way doors), unlike the two-way turnstiles of New York. Moreover, unlike New York, Paris has no large emergency doors that can be opened. All passengers were going in one direction – out – so RATP should have propped the exit doors open to let passengers out more smoothly.

Free transit for special events is routine in Paris. The trains are free around New Year’s, in order to encourage people to take the train rather than add to car traffic and pollution (and perhaps drunk driving). Bastille Day celebrations and any future victory at the World Cup or Euro Cup should be added to the list of free transit events, not to discourage people from driving but to prevent stampedes.

And second, the city should have closed the surrounding area to non-emergency car traffic. Champs-Elysees was closed, but there wasn’t much place to spill over; the side street I took once I tried leaving had a narrow sidewalk, and police cars were parked in a way to restrict people to a constrained exit path. There is no parallel street that can act as a spillover route, and between the Rond-Point and Etoile there is only one crossing street wider than about 25 meters, Avenue George V on the south side (whereas almost all rail alternatives to the Metro Line 1 are on the north side). With narrow side streets, it’s especially important to dedicate space to pedestrians and emergency vehicles and not to cars. This was as far as I can tell not done, making it hard for people to leave the most crowded areas. In contrast, Etoile itself, with twelve avenues radiating from its circle, was not so crowded, as people had escape routes.

World Cup victories are rare enough that cities understandably don’t design their entire layout based on them. But when they do happen, it’s critical to have a plan, and the same is true of other big celebrations, which often occur annually on national days. If passengers are overwhelming the subway, it’s critical to quickly do whatever the agency can to increase throughput at station passageways as well as on the tracks. And if pedestrians are overwhelming the streets above ground, it’s critical to give them more street space, including for entry and exit.

Bus Branching

There are two standard reasons why public transit should limit branching. The first is that it reduces frequency on the branches; this is Jarrett Walker’s reason, and distantly the reason why New York doesn’t interline more than two subway services anywhere except 60th Street Tunnel. The second is that it makes schedules more fragile, first because services have to be scheduled more precisely to alternate among branches, and second because delays on one branch propagate to the others. And yet, rail and bus networks still employ branching, due to benefits including better coverage and focusing frequency where demand is the highest. This is especially common on regional rail, where all services are scheduled and often interact with the mainline network, so the second problem of branching is present no matter what. Metro systems instead have less branching, often because they only serve dense areas so that the main benefits of branching are absent. But what about buses?

I posit that bus branching is more valuable in low-density areas than in high-density areas. If an area only has demand for a bus every 30 minutes, and some farther-out places only have demand for an hourly bus, then it’s fine to branch the route in two. The bus would only be useful with some timed transfers at the inner end – maybe it’s feeding a regional train station with a train every half hour – but the Zurich suburbs have half-hourly clockface schedules with timed bus/rail connections and maintain high mode share for how low their density is.

In the other direction, look at Manhattan specifically. I’ve been looking at its bus network even though I’m only supposed to redesign Brooklyn’s. I’ve mentioned before that my epistemology is that if the presence of factor A makes solution B better, then the absence of factor A should make solution B worse. I noticed that the Brooklyn bus network has very little branching: the only route numbers that branch are the B41 and B38, and the only routes with different numbers that share the majority of their lengths are the B67 and B69 (which reverse-branch). However, Manhattan has extensive branching: the M1/2/3/4 share the Madison and Fifth Avenue one-way pair, and the M101/102/103 share the Third and Lexington one-way pair. Understanding why would be useful even if I only care about Brooklyn: if there is a good reason for Manhattan buses to branch then I should consider adding branching in Brooklyn where appropriate, and even if it’s inappropriate, it’s useful to understand what special circumstances make branching good in Manhattan but not in Brooklyn.

As it is, I don’t believe the branching in Manhattan is useful for Brooklyn. This comes from several reasons, at least one of which implies it’s not really useful for Manhattan either, and by extension for other high-density regions.

Base frequency

You can run a bus that comes every half hour on a schedule, making it possible to interline two hourly routes evenly. With some discipline you can go down to 15 minutes, or possibly even 10: Vancouver runs 12-minute limited buses on 4th Avenue on a clockface schedule with on-board fare collection and shared lanes, but there is signal priority at nearly all intersections and relatively little car traffic since the West Side’s street network is rich in arterial roads and distributes cars across other routes (i.e. Broadway, 12th, and 16th Avenues).

In contrast, it’s not really feasible to run buses on a schedule when they come every 5 minutes. There can be a printed schedule, but buses won’t follow it reliably. Once frequency hits about once every 3 minutes, regular street buses bunch so much that adding more buses doesn’t increase passenger capacity, but even in the 5-10 minute range, schedules are less important than headway management, unless the bus has extensive BRT treatments reducing schedule variance. This means that if a bus comes every 10 minutes and is scheduled on headway management, then branching the route means each branch gets service every 20 minutes scheduled on headway management as well. Few passengers would want to ride such a route. This is the worst region for branching, the 7.5-15 minute range in which branches force passengers to use buses that are both infrequent and irregular.

The highest-frequency routes can branch with less risk. If a 5-minute bus branches in two, then each branch gets 10-minute service, at which point reliable schedules are still desirable but not absolutely necessary. How much service do the Manhattan bus trunks run? In the following scheme, peak means the busiest hour in the morning in the peak direction, and off-peak means the lowest frequency between the morning and afternoon peaks, which is usually around 11 am.

M1: 13 buses per hour peak (8 limited, 5 local), 5 off-peak (all local)
M2: 9 peak, 4 off-peak
M3: 6 peak, 6 off-peak
M4: 12 peak (5 limited, 7 local), 6 off-peak (all local)

M101: 6 peak, 6 off-peak (8 in the busiest off-peak hour, 2-3 pm)
M102: 5 peak, 4 off-peak
M103: 5 peak, 4 off-peak

What we see is that Manhattan branches precisely in the worst frequency range. The buses are frequent enough that it’s not possible to run them on a timetable without either much better segregation from traffic than is feasible (even waving away politics) or massive schedule padding, but they still require passengers in Upper Manhattan to wait 10-15 minutes for their specific branch. One might expect that Bus Time would make it easier on passengers by telling them where the bus is, but no, ridership has actually fallen since apps were introduced (and this fall predates the entry of app-hailed TNCs into the city). It turns out passengers like being able to rely on easily memorable clockface schedules, or else on frequencies so high that they only need to wait 5 minutes, not 15.

The street network

Even one-time visitors to New York notice that the avenues in Manhattan are all one-way. This features prominently in the Manhattan bus network, which employs consistent one-way pairs on First/Second, Third/Lex, Madison/Fifth, and Ninth/Tenth. Moreover, again as every visitor to New York knows, Central Park occupies a large blob of land in the middle, interrupting Sixth and Seventh Avenues.

The upshot is that there are more north-south routes north of 110th Street than south of it. This is roughly the branch point on the three trunks that branch (First/Second only carries the M15). In Harlem, there’s demand for buses on Lenox (i.e. Sixth) and Seventh, both of which are two-way there. There’s also commerce on an interpolating route, Manhattan/St. Nicholas, which is effectively 8.5th Avenue in most of Harlem. Farther west, Ninth/Columbus is no longer a useful through-route north of 110th, but instead Tenth/Amsterdam is two-way, and one of the two buses using the Columbus/Amsterdam one-way pair on the Upper West Side, the M11, indeed goes two-way on Amsterdam north of 110th.

This situation occurs very frequently in cities without gridded street networks. One trunk route will split in two, heading to different former villages that were incorporated into the city as it industrialized and grew. Manhattan is unusual among gridded cities in that its avenues are one-way, forcing buses into one-way pairs south of Harlem that, together with Central Park, ensure there are more useful routes north of 110th than south of it. But among cities without a planned street network this is typical.

As a check, let’s look at the bus networks in two ungridded American cities: Boston and Providence. Do they have a lot of interlining, involving one trunk route splitting in two farther out? Yes, they do!

Here is Providence. Going west of Downcity, there are two major routes to Olneyville, Westminster and Broadway, but beyond Olneyville there are four main streets, so each of the two inner corridors carries two bus routes, and one of these four routes even splits in two farther out. Going north, Charles Street carries four routes, branching off at various locations. Going east there’s a bus tunnel to College Hill carrying many routes, but even outside the tunnel, the one-way pair on Angell and Waterman carries three buses, which split in East Providence. And going south and southwest, Broad Street carries multiple routes, and one of its branches, Elmwood, carries two, splitting farther south.

Here is Boston. Unlike in Providence, buses don’t converge on city center, but on subway stations, so the map is much less clean. However, we see the same pattern of trunk routes splitting into branches. For example, going south of Ruggles, many routes go southeast to Dudley and then south on Warren Street, splitting to various destinations in Dorchester, Mattapan, and Hyde Park on the way. Going southwest of Forest Hills we see many routes use Washington Street, some staying on it and branching in Dedham and some veering west to West Roxbury and branching there. Elsewhere in the system we see the same pattern going north of Maverick and Oak Grove, northeast of Malden, west of Harvard (briefly on Mount Auburn), and northwest of Alewife.

One-seat rides and reverse-branching

I have repeatedly criticized the practice of reverse-branching on subway networks, especially New York, in which two train routes share tracks in an outlying area (such as Queens Boulevard) and then split heading into the center (such as Eighth Avenue on the E versus Sixth Avenue on the F). I did so on the same grounds that any branching is suspect: it reduces frequency on specific routes, and makes the schedule more fragile as delays propagate to more of the network. Moreover, the issue of schedule fragility gets worse if many routes share tracks at some point during their journey, whereas with conventional branching there are only two or three branches per trunk and the trunks form self-contained systems. Finally, reverse-branching lacks the main benefit of conventional branching, as it does not concentrate traffic in the core, where there’s most demand.

These issues are present on bus networks, with two modifications:

  1. The value of one-seat rides is somewhat higher. Transferring between buses is less nice than transferring between subways: in a Dutch study about location decisions, people’s disutility of out-of-vehicle time on buses was 1.5 times as high as on trains.
  2. Buses can overtake each other and, even without overtakes, run much closer together than trains. The limiting factor to capacity on buses is schedule fragility and bunching and not stopping distances. This means that reverse-branching is less likely to lead to cascading delays – buses do not have a 2-minute exclusion zone behind them in which no buses may enter.

This means that reverse-branching is more defensible on buses than on trains. However, even then, I don’t think it’s a good idea. At least in Manhattan, reverse-branching consists of avenues in Upper Manhattan that have buses going to both the East Side and the West Side: the M7 (serving the Ninth/Tenth pair) and the M102 both run on Lenox, and the M4 and M104 (running on Broadway to Midtown) both run on Broadway in Morningside Heights. These splits both reduce the frequency available to bus riders and should be eliminated. East-west service should be provided with high-quality bus routes on the main streets, especially 125th (which needs a full subway) but also 116th, 135th, 145th, and 155th.

The snag is that grids don’t work well unless they are complete. The Manhattan grid isn’t complete through Upper Manhattan, because 116th and 135th are discontinuous, without a direct connection from Central Harlem to Morningside Heights and West Harlem. However, the M7 route duplicates the 2 and 3 trains, so it’s not necessary for east-west connectivity. The M4 route doesn’t duplicate the subway, but does duplicate the M101, which runs on 125th Street and Amsterdam (and isn’t a reverse-branch because the M11 terminates shortly after 125th), so it’s not useful by itself.

Should buses branch?

There is one solid reason for buses to branch: if the street network has more major routes closer to the center than in outlying areas, then buses running on the outer arterials should come together close to the core. This is common enough on cities with haphazard street networks. It may also be reinforced if there are weak circumferential streets (Sydney is one such example). In contrast, cities with gridded street plans, even broken grids like those of Brooklyn and Tel Aviv, should have little to no bus branching.

If a bus does branch, it should ideally be extremely frequent on the trunk, so that even the branches have decent headway-based service. I’m not willing to commit to a maximum headway, but Barcelona and Toronto both have at worst 8-minute headways on their bus grids, so if that is indeed the maximum then a bus shouldn’t branch if its off-peak frequency is worse than every 4 minutes and better than every 10-20 (the more reliable the timetable is, the lower the upper limit is, since it’s possible to run on a timetable at higher frequency). In my case of interest, Brooklyn, there is exactly one bus route that comes at least every 4 minutes off-peak: the B46 on Utica runs 16 buses per hour in each direction, counting both local and limited (SBS) routes.

The area in which buses absolutely should not branch – strong interconnected networks of arterials (not necessarily grids – Paris’s network counts too), running buses every 5-15 minutes off-peak – is exactly where most strong bus networks are. It’s rare to have a bus that has extremely high frequency all day, because in most functional city such a bus would be a subway already; as it is, Utica has long been New York’s second priority for subway service, after Second Avenue. So for the most part, the places where buses are the strongest are precisely those where branching is the most deleterious. Low-frequency networks, perhaps connecting to a suburban train station with a timed transfer, should add bus branching to their planning toolkit, but high-frequency urban networks should not.

Where are Transportation and Housing Politics Going?

It’s hard to escape the conversation about the decline of the center-left. Whether it’s about non-populist US Democrats, the Israeli Labor Party, Nordic social democrats, German SPD, or French PS, there’s a pan-first world conversation about the crisis of social democracy. People give any number of reasons for it, some suggesting it can be reversed in some ways, but some more skeptical. Branko Milanovic brings up the change in the nature of work from manufacturing with interchangeable workers within one plant to services with fractionalized workers often working remotely as an economic cause of the decline of unions.

Public transportation is sufficiently close to social democracy that it’s important to ask where it’s going politically, if SPD is slipping to third in the polls, PS is irrelevant, the most exciting Democrats are left-populists, etc. YIMBYism can go anywhere politically, but in practice it’s an anti-populist neoliberal policy, affected by the same trends that hollow out social democracy. Fortunately, both issues have a strong likelihood of surviving the decline of the traditional party system with its bosses vs. workers divisions. My goal is to explain why I believe so, and where support for urbanism and public transit will end up politically in the remainder of the century in developed countries.

Patterns of Democracy

In college I read Patterns of Democracy, a study by comparativist Arend Lijphart classifying the world’s stable democracies (including some third-world ones like India and Botswana) along two dimensions: majoritarian (i.e. two-party) vs. consensus-based (i.e. multiparty), and federal vs. unitary. It’s a book-length overview of the elements that go into each dimension, culminating in some regressions showing that majoritarian democracies are not more politically stable and do not economically overperform multiparty ones.

For the purposes of this post, the interesting part of the book is how it treats the various dimensions of partisan political debate within each country. The most popular analysis is one-dimensional left vs. right, followed by two-dimensional schemes separating economic and liberal vs. authoritarian issues (on the Internet, this is Political Compass). But Lijphart uses a seven-dimensional analysis (pp. 76-78), with each country only having at most three or four active at a time:

  1. Socioeconomic issues, by far the most common point of controversy within each democracy, including the usual left-right issues like tax rates, health, education, etc.
  2. Religious vs. secular issues, such as the role of religion in education, abortion rights in the US, or sectarian conflict in multisectarian states like Israel, India, and the Netherlands.
  3. Cultural-ethnic issues, which in most countries pit majority-group hegemony against multiculturalism, but can also include Belgian language politics or Ashkenazi-Mizrahi tensions in Israel.
  4. Urban vs. rural issues, such as farm aid.
  5. Regime support, historically the main cleave between social democratic and communist parties, and today the cleave between extreme right parties like the National Front and AfD (or individuals like Donald Trump) and hard right mainstream parties like Sarkozy and Wauquiez’s Republicans and CSU (or individuals like Ted Cruz and Scott Walker).
  6. Foreign policy, for examples decolonization in postwar France and Britain and the conflict with the Palestinians in Israel.
  7. Post-materialist issues, including the environmental issues that underlie the New Left, representing the cleave between social democratic and green parties.

The decline of class-based politics

The crisis of social democracy that Milanovic and others observe is about the decline of class-based politics, pitting workers versus bosses, or the working class versus the middle class. Economic differences between mainstream parties are decreasing, to the point that grand coalitions (as in Germany) or de facto grand coalitions (such as the cordon sanitaire agreement in Sweden excluding the far right) are normalized, joined by an elite consensus that’s for the most part neoliberal. In their stead, the growing issue in salience in Lijphart’s classification is cultural-ethnic, incorporating the sectarian aspects of the religious-secular dimension, including immigration, multiculturalism, and various forms of racism.

However, it’s better to divide socioeconomic issues into issues that are class-based and issues that are not. The most familiar issues across the developed world today pit the rich against the poor: tax rates, health care, education, welfare, unions, labor regulations.

But a large number of issues divide people in different industries, with a fair degree of agreement between labor and capital within each industry. One such issue is the environment, on which oil executives and oil rig workers tend to vote the same way while executives at green tech or low-energy intensity companies and their workers tend to vote the other way. Another issue is free trade, where the battle lines today separate import-competing industries from exporters and industries that rely on a global supply chain (including finance). Historically, the Populist movement in turn-of-the-century America was rooted in farmers’ grievances, demanding free silver, which had little appeal to either the bourgeoisie or the urban working class, which channeled its disaffection into socialism instead. Thus the set of non-class-based economic issues should take over Lijphart’s urban-rural and postmodern dimensions.

Transportation as a politically contentious issue has always had one leg in rich vs. poor politics and one leg outside it. On the one hand, the poor generally use public transit more than the rich, and historically suburbanization in the US as well as the UK was fueled by middle-class flight from the city. On the other hand, the issue intersects with environmentalism and with urban-rural politics. Within cities, the differences often revolve around one’s job descriptions: people who need to drive for a living, such as plumbers and generally people who work outside the CBD, are more hostile to road diets than people who do not, who include both professional downtown workers and downtown service workers.

Non-class-based economic issues are not in any decline. On the contrary, the parties designed around them, including green parties and left-liberal parties (such as D66 or the Danish Social Liberal Party), are for the most part doing fine, taking refugees from declining social democratic parties. In the Schröder cabinet, it was the Greens who pushed for an increase in fuel taxes; support for transit over cars will survive whatever happens to the center-left.

The new class divide

While labor vs. capital is increasingly not a big political cleave in the developed world, other class cleaves are rising to take its place. Non-class-based economic issues pit different industries against one another, and often there’s no consistent pattern to who is on what side, and the same is true on non-economic issues. However, in a large number of cases, there is a consistent pattern, which can be approximated as liberal versus conservative, in the 19th century British sense.

In the case of YIMBYism, the debate over housing is really a fight between two elite classes. The YIMBY side is represented by the professional middle class; the other side is represented by homeowners. Moreover, the professional middle class tends to specifically come from globalized industries, drawing workers from all over, most famously tech in the Bay Area. This class has high labor income and low capital income as well as local social capital, which explains both YIMBYs’ indifference to preserving property values and preference for preemption laws disempowering local notables. Homeowners are the exact opposite: they tend to have high local property values and local social capital relative to their labor income, which means they favor restrictions on housing construction economically and a hyperlocal process in which they’re privileged participants politically.

For the most part, other non-economic issues correlate with the same cleave between the two elites. Middle-class newcomers are overwhelmingly attracted to production amenities of specific global industries (again, Bay Area tech, but also New York and London finance, Paris conglomerates, etc.), which benefit from free trade and have such diverse worker bases that they fall on the liberal side of most debates over immigration. They also tend to cluster in specific job centers, which are at least in principle serviceable by public transportation, leading to high transit ridership relative to income. The urban jobs that are most likely to require driving are local services, which are overwhelmingly owned by people who either were born in the city or immigrated so long ago that they are politically and socially equivalent to natives.

I bring up 19th-century Britain and not the US because Britain had an alignment between free trade, urban over rural interests, and internationalism in the Liberal Party, whereas in the US the Democrats were also the white supremacist party and (outside the Northeast) the agrarian party. But 19th century Europe fits the situation in the first world today between than the 19th century United States, which had free land (courtesy of the Indian Wars) and no real landed gentry apart from the antebellum Southern planter class.

So where are the poor?

If both sides of the debate over zoning and urban housing production are middle-class elites, then where is the working class? The answer is, nowhere. There are working-class organizations on the NIMBY side, such as tenant unions and community groups that try to extract maximum value from developers. There are also poor people on the YIMBY side: in the Houston zoning referendum the poor voted against zoning and the middle class voted for, with poor blacks voting the most strongly against zoning, and at a recent hearing in Brooklyn for a mixed high-rise project most whites spoke against the project and most nonwhites spoke in favor.

To the extent there’s a pattern, organized local groups of poor people and/or minorities are NIMBY and generally unreliable about public transit, but when it goes to ballot there is not much difference between how the poor and middle class vote. Organized local groups of the middle class aren’t any less NIMBY than organized low-income groups, but the middle class more readily dismisses local activists as crackpots and nincompoops. It matters that political activists with more talent and ambition than the typical king of a hill can advance to higher levels of government if they come from favored socioeconomic strata.

The situation with public transit remains profoundly different, because it really does maintain some class-based content. But in general transit cities, even flawed ones like New York, tend to have alignment between working- and middle-class organizations in favor of more investment, and then questions like congestion pricing, bus lanes, bike lanes, and pedestrian plazas cut across class lines and cleave people based on where they work and how they get there. In my Brooklyn bus redesign project, I expect allies to include the bus drivers’ union (the drivers are strong supporters of reforms speeding up buses, since they’d make their work safer and more comfortable) and middle-class reformers and opponents to include working- as well as middle-class drivers (since we’re going to propose stronger bus lane enforcement and street redesigns that prioritize buses). Overall drivers outearn transit riders, but the difference tends to be smaller in cities with even semi-decent public transportation than in places like Los Angeles, where transit is so bad that most riders are people too poor to afford a car.

The result is that it’s very easy on both sides to dismiss the other side as an elite fighting the working class, even in public transit (since a substantial segment of the working class really does drive, even though it’s a smaller segment than in the middle class). In reality, on non-class-based issues it’s hard for the poor to truly be relevant as political actors. In the bus redesign project the union has a voice, but the premise of this post is that the political power of unions is in decline; public transit just happens to be an industry that, owing to its Fordist layout, is unusually friendly to unionization, at least until driverless buses are deployed at scale.

In this context, people should avoid dismissing their opponents as rich. Both sides have vanguards that are mostly middle-class, with some rich people sprinkled around. It’s a fight between two elites, and the YIMBY elite has grounds to portray itself as superior to the NIMBY elite, as it’s defined by skilled professions rather than passive property income, but it’s still a privileged elite and not the poor.

Whither transit and urbanism?

I already see some evidence that support for mass transit and urban growth (which mostly, but not exclusively, means YIMBY) is concentrated in the segments that are underlying where left-liberalism is going. New Left parties, including center-left ones (i.e. D66 and the Danish Social Liberals), are fans of transit. Greens tend to have a small-is-beautiful mentality toward cities, but I believe that this will change soon as green parties become vehicles for more internationalist voters, just as these parties flipped last decade from euroskeptical to europhilic.

What this means is that transit and urbanism as politics are likely to remain important political issues and if anything grow in salience, as they play well to growing cleaves between urban and rural, or between international and local. Whatever happens to specific political parties, these issues will survive.

Why is Tramlink So Weak?

I’ve mentioned on Twitter that I’m visiting London. I’m taking a lot of railfan trips, one of which was on Tramlink, London’s circumferential light rail service. Tramlink runs in South London, from Wimbledon in the west to Croydon in the east and thence along several branches to southeastern outer neighborhoods. Much of the route uses former mainline rail rights-of-way that were only partly grade-separated. The trains satisfy all of TransitCenter’s principles for good light rail operating practices, but their ridership is lackluster by the standards of Paris, TransitCenter’s comparison city. Tramlink has 30 million annual riders on 28 km of route, or about 3,500 per km per weekday; Ile-de-France’s system had 900,000 daily riders in 2015 on about 100 km route, or 9,000 per km. My goal is to explain why. One reason involves route choice, but the main reason is lack of development; this problem is very common in other cities, and must be added to the other pitfalls that TransitCenter mentions.

The operating practices on Tramlink are not bad. The frequency is high: every 5 minute off-peak. There’s no fare integration with the proper rail network (including the Underground), but the buses in London have no fare integration with the trains either and still have high ridership. The connections with radial train lines are decent, though there’s one big miss (with the Northern line) and one smaller one (with West Croydon, which points to train stations that are served by other lines that do get interchanges); the two most important transfers, Wimbledon and East Croydon, require relatively little walking between platforms. The right-of-way quality is high by light rail standards, mostly in a private right-of-way with only a small extent of street running within Croydon; the average speed is 21 km/h (higher than the Parisian tramways – T3 averages 18 km/h). And yet, ridership is not so strong. London is a big city with high rail ridership, so it’s not a matter of a small city underperforming Paris on raw ridership; something deeper is wrong with Tramlink.

Part of the problem has to involve route layout. East of East Croydon, the route has three branches. Two, heading to Elmers End and Beckenham Junction, keep the route’s circumferential character; in theory it should be faster to take mainline rail and change trains than to ride Tramlink, but in reality the mainline routes that would be used have missed connections and therefore are not useful for diagonal trips. Each of these two branches runs every ten minutes, interlining to a train every five minutes between East Croydon and Wimbledon. However, a third route connects East Croydon and New Addington, a radial line, running every 7.5 minutes. This route does not run through to Wimbledon (which would be a radial-circumferential mix) and exists as an orphaned feeder line, sharing tracks with the two main branches just east of East Croydon (thus, creating schedule conflict due to the uneven frequency on the shared trunk).

But the main difference between Tramlink and the Parisian tramways is adjacent density. London is generally a less dense city than Paris. London has two- and three-story rowhouses with back gardens where Paris has five- to nine-story buildings with high lot coverage. The Tramlink route itself is even less dense, passing through suburbia, industrial sites, and golf courses. The Parisian tramways are all in the suburbs (except for T3), but serve high-density clusters, surrounded by a mixture of mid-rise buildings and social housing towers. This is especially true on the workhorse Parisian routes – T1, T2, and T3, which collectively have about three quarters of the system’s total ridership – but even the other routes, while much weaker than the main three, serve denser areas than Tramlink and get higher ridership per kilometer.

Here is a randomly-selected station on T2, Meudon-sur-Seine:

Compare it with Mitcham, one of the more populated stations on Tramlink between Wimbledon and Croydon:

Also compare both with the site of the missed connection with the Northern line, Morden Road:

I want to make it very clear that the two satellite maps of Mitcham and Morden Road are not representative of all of South London, certainly not when weighting by population. East Croydon is full of mid- and high-rise TOD, and to some extent so is Wimbledon; the two stations rank fifth and sixth in ridership in London excluding the Central London terminals. The problem is that a circumferential line is rarely used over a long stretch. The longer the angle subtended on a circumferential line, the more favorable it is to take the radials and transfer.

London in particular has four-track mainlines on most rail routes, including the London and South Western Main (serving Wimbledon) and the Brighton Main (serving East Croydon), making it easy to run express routes. Every hour, there are 9 trains running nonstop between East Croydon and Clapham Junction, and 16 trains running between Wimbledon and Clapham Junction with two intermediate stops. The diagonal commuter rail trip is faster than Tramlink, even counting transfer time at Clapham Junction.

Paris is full of express trains, represented by the RER. But T3 misses nearly all of the RER connections, which weakens the route but also means that there is no express alternative on the outer margin of Paris; but one would still not take it all the way, especially since there is a forced transfer at Porte de Vincennes. But T1 and T2 have better RER and Transilien connections. The high density all along these routes, and not just at widely-separated key junctions, ensures that there is high demand even on short segments.

In fact, there is circumstantial evidence that T1, T2, and T3 have extensive short-range ridership: their ridership levels per kilometer are very high (respectively 11,000, 12,000, and 15,000 per weekday), and if they had low turnover they would not have capacity for such high ridership. New York has 15,000 weekday subway riders per route-km, and this is with long trains, extensive four-tracking, and higher peak frequency than on the Parisian tramways. It’s hard to imagine comparable ridership levels on a surface tramway without very high turnover, which I have in fact observed riding T3.

In contrast, I saw relatively little turnover between Wimbledon and East Croydon on Tramlink. I saw some, generally involving a small net decrease in passengers on the tram at the first few stations past Wimbledon, but a large proportion of passengers who got on at Wimbledon stayed on until Croydon. To them, the tram is perhaps a slower but cheaper alternative to mainline rail. Some would also ride until one or two stations before East Croydon, within the built-up cluster of Croydon; perhaps their exact destination was closer to one of these tram stations than to East Croydon, where the tram loses a lot of time due to circuitous street running.

Reinforcing the importance of turnover, the tram was crowded. I took it at 4:30 in the afternoon, on the shoulders of rush hour, and it was standing-room only for my entire trip, with considerable crowding among the standees for the first few stations. And yet, despite the crowding, ridership per kilometer is a fraction of that achieved by Paris’s top three tramways, which do not appear more crowded.

I wrote about turnover in the context of Vancouver buses, talking about patterns of development along north-south arterials (Main, Fraser, and Commercial) versus east-west ones (King Edward and 49th). Here we see how it interacts with development on a circumferential tramway within the context of a rapid transit network with fast radial lines. It’s common in a large city to have strong demand for circumferential transit but not so much that full rapid transit is justifiable, leading to tramway networks such as Tramlink and the tramways of Ile-de-France. In this context, it’s important to attract short-hop ridership and not just end-to-end ridership, where the tramway would struggle with the radial rapid transit network. This in turn requires the region to ensure that the intermediate stops generate ample ridership, which requires either uniformly high density (as is the case in and around Paris) or a deliberate effort at TOD in the middle.

This is true for more than just tramways. The fundamental fact about Tramlink and the Ile-de-France tramways is that they are slower than their respective cities’ radial rail networks. The same fundamental fact is true of circumferential buses, even in cities where the radial rail network is light rail rather than rapid transit. In theory this could even happen in an all-bus city, provided the buses’ right-of-way quality were such that the radials were faster than the circumferentials; but in reality this is hard to arrange, since buses get stuck in traffic even when they’re BRT, and there’s more traffic near city center than outside.