Category: Urban Design

Rapid Transit in Low-Density Boomtowns

Most of my thinking about public transit comes from large, dense cities, especially New York. In those cities, transit ridership is not a problem; only cost is. When such cities have decent cost control, they can build massive expansion programs, as Paris is. But most of the developed world is not New York, Paris, London, Tokyo, or other transit cities. A large and (thanks to differential national population growth rates) growing share of the developed world lives in fast-growing, low-density city regions with no public transit to speak of, such as the American Sunbelt and its counterparts in Canada and Australia.

I’ve had to intellectually grapple with public transit in two American Sunbelt cities in which current transit usage is a rounding error and the built form is wholly auto-oriented: Orlando (which I was asked about by a Twitter mutual) and Nashville (which just voted against a flawed light rail plan by an overwhelming margin). In those areas, there is no chance for any public transit, provided the urban form stays as it is – but fortunately such cities can leverage their high growth rates to change their urban form, as Calgary did in the 1980s and 90s.

Density versus growth

A few months ago I made this chart:

The density and growth demand axes are not meant to come from a single quantitative metric; density is a subjective mix of residential and job density, whereas growth demand refers to either population growth or the demand for more housing as expressed by price signal. In San Francisco, most likely the richest metro area in the world, density is middling, and growth demand is higher than even in New York and London; in the American Rust Belt, density is fairly low and there is also little demand for more; in some cities on the margin of the first world there is little demand for more growth but high preexisting density. It goes without saying that it’s easier to build new rapid transit lines on the upper right corner than on the lower left one.

The situation of the American Sunbelt, most of which goes in the bubble of Texas and Georgia, is difficult. Residential density is extremely low, so the ridership base near potential rail lines is low. Moreover, streets are usually designed exclusively around auto use, so passengers are unlikely to walk a kilometer to the train station the way they routinely do in transit cities. At the destination end, things aren’t much better – American cities have high-rise CBDs, but few jobs locate there or in surrounding dense neighborhoods.

The Orlando CBD has about 80,000 jobs, in a metro area of 2.5 million people. Disney World adds another 37,000, but is not surrounded by any serviceable residential neighborhoods, and has to be at the end of any reasonable transit service coming from the CBD. Nashville, a metro area of nearly 2 million, has a CBD with 36,000 jobs. The medical center to the southwest adds another 33,000, and this time it could plausibly lie on a rail trunk, but most of the useful urban arterials converge on the CBD and not on the medical center. In contrast, Washington, with 5.5 million people, has 280,000 people working at the CBD (from the Green and Yellow Lines to just beyond Dupont Circle and Foggy Bottom), 77,000 in the Rosslyn-Ballston corridor, and 33,000 in Crystal City and at National Airport and the Pentagon. Both the percentages and the absolute numbers (including job density) count: there is a great mass of people who would be interested in taking rail to Washington CBD jobs but not to Orlando or Nashville CBD jobs.

Can regional rail work?


High-growth areas are likely to have been small a few decades ago. For the most part the metro areas in question were too small in the heyday of rail transportation to have inherited a large legacy rail network. Even the ones that did, including Atlanta and Perth, have less legacy rail than older cities of comparable size – compare Atlanta with Philadelphia, or Perth with Brisbane. And most North American boomtowns are not Atlanta. Miami has two north-south mainlines and a handful of east-west connections, none at the right place for commuter rail. Orlando has a north-south trunk with a branch to the north, and Nashville a few branches, but they’re surrounded by industrial land use and not by the sort of suburbs that developed around commuter rail in the Northeast.

A commuter rail-based network can still work, but only with extensive greenfield lines. Disney World is not on any legacy rail line, because it developed long after rail stopped being a relevant mode of transportation outside large urban areas. But even then, gaps in coverage are unavoidable, as the dense neighborhoods of such cities did not develop around legacy rail.

Can transit-oriented development work?

Sort of.

The big question about TOD is, who is it for? In Nashville specifically, the far left opposed the light rail plan, essentially because it would cannibalize funding that could go to public housing. Now, public housing could be used to beef up density along rail corridors. Stockholm built public housing simultaneously with the subway, placing housing projects on top of rail branches, and as a result has per capita ridership today that’s not much lower than the level of Paris, Berlin, or Munich.

The problem is that public housing is horrendously expensive. A house in low-cost American cities costs around $150,000, but apartments cost more, so $200,000 per household is more likely even with some economies about size. Most of this cost is impossible to recover through rent – if low-income households made enough money to pay market rent in nice apartments, they’d just rent these apartments on the open market. The American Sunbelt does not lack for developable suburban land.

Market-rate housing is much easier to construct – for one, developers make a profit on it, and so are eager to put up their own money. The problem is that in cities like Nashville and Orlando, the middle class has close to 100% car ownership, and a large majority of households have one car per adult. The real estate industry is not going to spontaneously build housing with less parking or pedestrian-oriented retail.

In San Diego, developers build more parking than the minimum at University Avenue and 30th Street, according to Duncan McFetridge of the Cleveland National Forest Foundation. University is a bus corridor and not a light rail corridor, but the bus frequency there isn’t terrible, and the area is pretty walkable for a low-density city. In Los Angeles, I’ve read analysis that blames the region’s falling transit ridership on gentrification, explaining that in gentrifying inner neighborhoods like Boyle Heights, the middle class drives whereas the working class takes transit. It’s not like here or in New York, where recent gentrifiers rarely own cars.

How did Calgary make it work?

Calgary is a metro area of somewhat more than a million people. Its economy is based on oil, and when oil prices were higher earlier this decade its average income was comparable to that of San Francisco; its politics is thoroughly conservative, which means there is no progressive impetus for walkability or green transit. Nonetheless, it built light rail lines that get about 100 million annual riders today. Its transit mode share is 16%, higher than that of any American metro area except New York (or, in the most restrictive definition, San Francisco). This is with no residential TOD to speak of: the vast majority of housing in Calgary is single-family and low-density, and from what I’ve seen there’s almost no dense residential development near the stations.

The big thing Calgary did was develop its CBD to be high-rise. In the early 1980s Calgary was a small, monocentric city, and since then it’s grown more monocentric, developing downtown parking lots as high-rise buildings. When I visited it had a more prominent high-rise downtown than Providence, a bigger and older metro area, and walking between the high-rises was reasonably pleasant.

In low-density cities with demand for more growth, the best opportunity appears to be centralizing jobs in the CBD. The straightforward application involves developing parking lots, as in Calgary, and relying on the private market to do the rest of the job. In both Nashville and Orlando, there are also more proactive approaches, specific to their urban layouts. In Nashville, the high job density at the medical center calls for developing a continuous corridor from the CBD, about 3 km long. This corridor could plausibly get an east-west subway, in contrast with the north-south subway in the rejected light rail plan. In Orlando, the Disney World cluster calls for some residential upzoning and sprawl repair around that area, which would strengthen the case for building a rail line between that area and the CBD.

Growing cities can use their growth to support more auto-oriented development (as the big American cities did in the postwar era) or to support more public transit. This is understood in cities that already have a transit-oriented core, but it’s equally true in cities that don’t really have any public transit, like the entire American Sunbelt. Calgary, starting with very low population, managed to build a decent if not great public transit network centered on its light rail system, and the same should be doable in American cities of comparable size and age.

Urbanism and Standards of Respectability

Alex Baca wrote a thread on Twitter a week ago, talking about cities and normativity. The key tweet is,

The discourse about ~cities~ is, to me, a big fight against a normative, hegemonic, mostly white, mostly straight dominant culture, which has very clearly not made physical space for people who don’t fit that profile. It sucks, and we’re seeing the effects.

A few days later, I saw an unrelated meme, attacking Scott Wiener, the state senator representing San Francisco, who supports the YIMBY movement and introduced a zoning preemption bill that would permit mid-rise construction and abolish parking minimums near public transit. The meme consisted of two photoshops:

My first reaction to seeing the first picture was “I live in a building just like this.” I lived adjacent to buildings like the ones in the second picture in Singapore (where they’re actually taller) and the French Riviera. I’d already been thinking of different standards of middle-class respectability, in large part thanks to Alex’s thread, but the memes crystallized this so perfectly.

There’s a certain American standard of middle-class normality. A detached house for a nuclear family, with a backyard for the children to play in, and a garage that fits a car per adult. A school that has as few black students as possible without making the white middle class feel too guilty. Social engagements and hobbies that are so common, like a knitting circle, that a suburb of 10,000 can support a group. Everything else is deviant and embarrassing.

This is not the only middle-class respectability standard out there. There’s a competing standard, common in countries without a history of white flight. In cities with good transit, like Stockholm and Paris, generations can grow up and live in the city in apartment buildings and not own cars. Car ownership is still higher in richer areas – transit ridership is very far from universal in Paris, even intra muros – but it’s not mandatory. Detached housing is also less common even among the most comfortable segments of the middle class. The Singaporean dream is to own a car and live in a condo. The Israeli dream always includes a car but runs the gamut on density, from detached houses through mid-rises to high-rise condos in Tel Aviv.

Academia has lower car ownership than other professions of equivalent income, but still exhibits the same difference in mentality. My former postdoc advisor at KTH, a tenured professor, biked to work. At my last math conference, in Basel, one professor complained that when they tried biking to work when on sabbatical at the University of Michigan they got strange looks from the rest of the department. “Ann Arbor is a left-wing city and they still drive,” the professor said. In the United States, math postdocs usually don’t own cars but tenured professors do and often live in the suburbs, even at Columbia.

New York is supposed to have good transit and urban amenities, but for the most part the middle class treats it as part of a life cycle in which families live in the suburbs, rather than as a stable place. The city’s poverty rate is 20.3% per the 2012-6 American Community Survey, but among children age 5-17 it’s 29.3% (and among under-5 children it’s 27.7%). In my largely middle-class American social circle there are a number of New Yorkers, but also a number of people whose parents moved from New York to segregated suburbs when they were born or when they were about to start school. Even on the level of urban layout, there’s a stereotype that the city is not a good place to raise a family, e.g. because the apartments are too small (in fact they’re larger than Parisian ones).

It’s not just a matter of different tastes – some people think respectability means the Mad Men lifestyle, some think it means living in a walkable city. The walkable city is capable of containing more than one standard of respectability, because it arranges itself to let people access more potential friends, who could form different social networks. In theory it’s possible to drive an hour in some suburbs and meet many people, but in practice it’s uncommon, for two reasons. First, it requires one car per adult, which is expensive and produces class stratification even in social groups that could be cross-class. And second, in practice the social identity of suburbs in the Northern US is local more than regional – for example, they tend to have smaller, more local schools.

In theory, conservative lifestyles could also be more supported in cities. Haredi Jews are very urban: they need certain community amenities like a kosher supermarket and a mikveh and have to live within walking distance of synagogue; when they suburbanize, it’s en bloc, like the Satmar move to Kiryas Joel or master-planned Haredi cities in Israel, often in the settlements.

In practice, this doesn’t happen. Haredi Jews are notable in being an oppressed minority in Israel as well as around New York. But traditional groups that view themselves as part of the majority end up wanting everyone to live like they do. When the Progressive Movement created the idea of suburbia around 1900, it came out of an explicit desire to assimilate immigrants into what it viewed as proper American values. The Historic American Engineering Record gives background about the politics of the subway both before and after construction. The point of suburbia from the start was to make it impossible to form any culture except the dominant WASP culture.

Not for nothing, urbanism in the United States tends to disproportionately feature people who have other reasons to be dissatisfied with traditional culture. Foremost among these are queers, who led gentrification in the 1970s and 80s, when they weren’t safe in most suburbs and small cities; even this decade, a genderqueer Canadian acquaintance told me that there are parts of the US that they’re scared to be in. Without outing people, I believe that between one third and one half of the people who write online about public transportation or urbanism in the US are queer.

In order to reinforce the notion that only single-family suburbs are the respectable way to live, American society has to denigrate everything else as ridiculous. Parisian apartment buildings feature a hammer and sickle and defenestration; Mediterranean apartment buildings feature gay flamboyance. Were the US more willing to admit that there are educated professionals in some countries that do not need a car, it would need to find ways to accommodate professionals with the same preferences domestically, and that would lead to accidentally accommodating people who are not in the social or cultural mainstream.

Suburban Transit-Oriented Development

Here’s a Google Maps image of Southport, a section of Fairfield, Connecticut with its own Metro-North commuter rail station:

Here’s an image at the same scale of Bourg-la-Reine, an inner suburb of Paris on the RER B, at the junction between the line’s two southern branches:

At Bourg-la-Reine, the buildings just east of the station are high-rise. There are local community amenities, including walkable schools, supermarkets, and pharmacies, and people can comfortably live in this suburb without a car. This generates significant RER traffic at all hours of day: outbound trains are often standing-room only until they reach this station even in midday, outside rush hour.

At Southport, there are a few townhouses near the station. But the roads are wide and hostile to pedestrians, and the nearest supermarket closes at 6 pm, too late for commuters returning from the city. Car ownership approaches 100%, and nobody rides the trains except to get to office jobs at the traditional peak hour in Manhattan (or perhaps Stamford).

The difference between the two places is so stark that they can barely be compared. Southport has 317 inbound boardings per weekday. Of those, 263, or 83%, are in the morning rush hour; the Metro-North-wide average is 63%, and the average on the SNCF-operated parts of the RER and Transilien is about 46%. Bourg-la-Reine has 4.5 million annual riders, about 16,000 on an ordinary working day.

A huge part of the difference is about service provision – Bourg-la-Reine has a train every five minutes midday, Southport a train every hour. But it’s not just about service. The RER has stations farther out, with somewhat less intense service, such as a train every 15 minutes, with comparable ridership. And the LIRR and Metro-North have little off-peak ridership even at stations with more frequent service, such as Mineola and Hicksville. Transit-oriented development (TOD) is as important as good service in such cases.

I bring up Southport because the RPA just dropped a study about suburban TOD that grades every New York commuter rail station between 0 and 3, and gives Southport the highest mark, 3. The RPA study looks at zoning within 800 meters of each station and considers whether there’s a parcel of land that permits multifamily housing with a floor are ratio higher than 1.25. Southport has such lots, supporting some townhouses, so according to the RPA it gets full marks, even though, by RER standards, it is like every other American car-oriented suburb.

Based on this methodology, the RPA identifies a number of good suburbs, and even comes to policy conclusions. It proposes more TOD in the mold of existing exurban New York examples, such as Patchogue. The model for the program is the real reason the RPA study is so weak: rather than calling into attention the big differences between land use at suburban stations in New York versus in Paris (or any number of big European cities with suburban rapid transit), it overfocuses on small differences within auto-oriented suburbia.

Some of the ultimate conclusions are not terrible. For example, the RPA is proposing linking federal infrastructure development to permitting more multifamily housing. This would improve things. However, the problem with this is twofold. First, it is unrealistic – the federal government gave up decades ago on enforcing fair housing laws, and has no interest in attempting to make exclusionary suburbs behave. Were I to propose this, hordes of American commenters would yell at me for not understanding American politics. And second, it misunderstands the nature of the problem, and ends up proposing something that, while unrealistic, is still low-impact.

The best way to understand the problem with the study is what author Moses Gates told me on Twitter when I started attacking it. He said that the RPA was looking at zoning rather than actual development. Since there is zoning permitting multifamily development within the prescribed radius at Southport, it gets full marks. With my understanding of what good TOD looks like, I would be able to say that this is clearly so bad the methodology must be changed; on Twitter I suggested looking at zoning within 300 meters of the station rather than 800, since the highest-intensity development should be right next to the station. I also suggested looking at supportive nonresidential uses, especially supermarkets. A development that isn’t walkable to retail at reasonable hours is not TOD.

The RPA does not think in this language. It thinks in terms of internal differences within the US. Occasionally it deigns to learn from London, but London’s suburban development is auto-oriented by European standards (transit mode share in the London commuter belt is at best in the teens, often in the single digits). Learning from anywhere else in the world, especially places that don’t speak English, is too difficult. This means that the RPA could not reach the correct conclusion, namely, that there is no such thing as an American suburb with TOD. The only exception I can come up with in the United States involves Arlington, on the Washington Metro, and Arlington is no longer considered a suburb, but really a full-fledged city in a different state, like Jersey City.

The other thing the RPA missed is that it drew too large a radius. TOD at a train station should include townhouses 800 meters out – but it’s more important to include high-rise residential construction next to the train station and mid-rise apartment buildings 500 meters out. Giving American suburbs latitude to place TOD so far from the station means they will act like Southport and allow small amounts of multifamily housing out of the way, while surrounding the station itself with parking, a tennis court, and large single-family houses with private swimming pools. This is not hypothetical: suburbs in New Jersey have reacted to court rulings mandating affordable housing by permitting apartments at the edge of town, far from supporting retail and jobs, and keeping the town core single-family.

Because the RPA missed the vast differences in outcomes between the US and France, it missed some useful lessons:

  • States should centralize land use decisionmaking rather than give every small suburb full autonomy.
  • TOD doesn’t need to be fully mixed-use, but there should be some local retail right next to housing.
  • Housing should be high-density right next to the station. A floor area ratio of 1.25 is not enough.
  • Publicly-funded social housing should be next to train stations, in the city as well as in the suburbs, and this is especially important in expensive suburbs, which aren’t building enough affordable housing.

Without suburban TOD, any regional rail system is incomplete. I wish I could have covered it at my talk, but I didn’t have time. Good service needs to run to dense suburbs, or at least suburbs with dense development within walking distance of the station. It needs to extend the transit city deep into suburbia, rather than using peak-only commuter rail to extend the auto-oriented suburbs into the city.

Safer Streets: Design is Better Than Enforcement

As some American cities are attempting to reduce the number of car accident fatalities, under the umbrella of Vision Zero, the growing topic is one of traffic enforcement. Streetsblog has long documented many instances in which the police treats any case in which a car runs over a pedestrian as a no-fault accident, even when the driver was committing such traffic violations as driving on the sidewalk. In addition to enforcement, there’s emphasis on reducing the speed limit in urban areas, from 30 to 20 miles per hour, based on past campaigns in Europe, where speeds were reduced from 50 km/h to 30. Unfortunately, street design for lower speeds and greater traffic safety has taken a back seat. This is not the best way to improve street safety, and is not the standard practice in the countries that have reduced car accident rates the most successfully, namely the UK and the Scandinavian countries.

On high-speed roads, one of the most important causes of fatal accidents is the combination of driver fatigue and sleepiness. For some studies on this problem, see here, here, and here. The second link in particular brings up the problem of monotony: if a road presents fewer stimuli to the driver, the driver is more likely to become less vigilant, increasing the probability of an accident. One study goes on and shows that higher speed actually increases monotony, since drivers have less time to register such stimuli as other cars on the road, but this was obtained in controlled conditions, and its literature review says that most studies find no effect of speed. I emphasize that this does not mean that lower speed limits are ineffective: there’s evidence that reducing highway speed limit does reduce accident rates, with multiple studies collected in a Guardian article, and lower accident rates in France since the state installed an extensive system of speed cameras.

But while speed limit reductions offer useful safety benefits, it is important to design the roads to be slower, and not just tell drivers to go slower. Road monotony is especially common in the United States; per the second study again,

While comparing self-reported driving fatigue in the US and Norway, Sagberg (1999) suggests that the higher prevalence of self reported drowsy driving found in the US may be due to differences in road geometry, design and environment, as well as exposure. He argues that the risk of falling asleep is higher on straight, monotonous roads in situations of low traffic, where boredom is likely to occur. This type of roads is more common in the US than in Norway.

The studies I have consulted look primarily at highways and rural roads; I have not found comparable literature on urban roads, except one study that, in a controlled simulation, shows that drivers are better at gauging their own alertness levels on urban arterials than on rural roads. That said, urban arterials share many design traits that lead to monotony, especially in the United States and Canada:

  • They are usually straight, forming a grid rather than taking haphazard routes originating from premodern or early-industrial roads.
  • They are wide: 4-6 lanes at a minimum, often with a median. Lanes are likely to be wide, closer to 3.7 meters than the more typical urban 3 meters.
  • Development on them usually does not form a strong enclosure, but instead commercial developments are only 1-2 stories, with setbacks and front and side parking lots.

Such roads are called stroads in the language of Charles Marohn, who focuses on issues of their auto-centric, pedestrian-hostile nature. Based on the studies about monotony, I would add that even ignoring pedestrians entirely, they are less safe than slower roads, which prime drivers to be more alert and to speed less. It is better to design roads to have more frequent stimuli: trees, sidewalks with pedestrians, commercial development, residential development to the extent people are willing to live on top of a busy road.

Regarding lane width, one study finds that roads are the safest when lanes are 3-3.2 meters wide, because of the effects of wider lanes on driver speeds. A CityLab article on the same subject from two years ago includes references to several studies that argue that wide lanes offer no safety benefit for drivers, but are hostile to pedestrians and cyclists.

This approach, of reducing speed via road design rather than enforcement, is common in Scandinavia. Stockholm has a few urban freeways, but few arterials in the center, and many of those arterials have seen changes giving away space from cars to public transit and pedestrians. Thus, Götgatan is partly pedestrianized, and Odengatan has center bus lanes and only one moving car lane in each direction; the most important of Stockholm’s streets, Sveavägen, has several moving car lanes in each direction, but is flanked on both sides by medium-rise buildings without setbacks, and speeds are rarely high.

When enforcement happens, the great successes, for example in France under the Sarkozy administration, involve automation. Red light cameras have a long history and are controversial, and in France, Sarkozy lowered the speed limits on many roads and stepped up speed camera enforcement. The UK has extensive camera enforcement as well. Human enforcement exists, but is less common than speed cameras. Thus, the two main policy planks Vision Zero should fight for in the US are,

  1. Road redesign: narrower lanes, wider sidewalks, trees, and dedicated bus and bike lanes in order to reduce the number of car lanes as well as provide more room for alternatives. Zoning laws that mandate front setbacks should be repealed, and ideally so should commercial height limits on arterials. In central cities, some road segments should be closed off to cars, if the intensity of urban activities can fill the space with pedestrians.
  2. Lower speed limits in the cities, enforced by cameras; fines should be high enough to have some deterrent effect, but not so high that they will drive low-income drivers bankrupt.

It is especially important to come up with solutions that do not rely on extensive human enforcement in the US, because of its longstanding problem with police brutality and racism. The expression “driving while black” is common in the US, due to bias the police in the US (and Canada) exhibits against black people. In Europe, even when bias against certain minorities is as bad as in the US, overall police brutality levels are lower in the US by factors ranging from 20 to 100 (see for example data here). In my Twitter feed, black American urbanists express reluctance to so much as call the police on nonviolent crime, fearing that cops would treat them as suspects even if they are the victims. When it comes to urban traffic safety – and so far, Vision Zero in the US is an urban movement – this is compounded by the fact that blacks and other minorities are overrepresented in the cities.

This means that, in the special conditions of US policing, it’s crucial to prevent Vision Zero from becoming yet another pretext for Driving While Black arrests. As it happens, it does not require large changes from best practices in Europe, because those best practices do not involve extensive contact between traffic police and drivers.

Recall last year’s post by Adonia Lugo, accusing Vision Zero of copying policy from Northern Europe and not from low-income American minority communities. As I said a year ago, Adonia is wrong – first in her belief that foreign knowledge is less important than local US knowledge, and second in her accusation that US Vision Zero advocates copy European solutions too much. To the contrary, what I see is that the tone among US street safety advocates overfocuses on punitive enforcement of drivers who violate the speed limit or break other law. Adapting a problem that in Europe is solved predominantly with street design and technology (speed cameras don’t notice the driver’s skin color), they instead call for more policing, perhaps because mainstream (i.e. white) American culture is used to accepting excessive police presence.

Greenbelts Help Cars

A number of major cities, most notably London, have designated areas around their built-up areas as green belts, in which development is restricted, in an attempt to curb urban sprawl. The towns within the green belt are not permitted to grow as much as they would in an unrestricted setting, where the built-up areas would merge into a large contiguous urban area. Seeking access to jobs in the urban core, many commuters instead live beyond the greenbelt and commute over long distances. There has been some this policy’s effect on housing prices, for example in Ottawa and in London by YIMBY. In the US, this policy is less common than in Britain and Canada, but exists in Oregon in the form of the urban growth boundaries (UGBs), especially around Portland. The effect has been the same, replacing a continuous sprawling of the urban area with discontinuous suburbanization into many towns; the discontinuous form is also common in Israel and the Netherlands. In this post, I would like to explain how, independently of issues regarding sprawl, such policies are friendlier to drivers than to rail users.

Let us start by considering what affects the average speed of cars and what affects that of public transit. On a well-maintained freeway without traffic, a car can easily maintain 130 km/h, and good cars can do 160 or more on some stretches. In urban areas, these speeds are rarely achievable during the day; even moderate traffic makes it hard to go much beyond 110 or 120. Peak-direction commutes are invariably slower. Moreover, when the car gets off the freeway and onto at-grade arterial roads, the speed drops further, to perhaps 50 or less, depending on density and congestion.

Trains are less affected by congestion. On a well-maintained, straight line, a regional train can go at 160 km/h, or even 200 km/h for some rolling stock, even if headways are short. The busiest lines are typically much slower, but for different reasons: high regional and local traffic usually comes from high population density, which encourages short stop spacing, such that there may not be much opportunity for the train to go quickly. If the route is curvy, then high density also makes it more difficult to straighten the line by acquiring land on the inside of the curves. But by and large, slowdowns on trains come from the need to make station stops, rather than from additional traffic.

Let us now look at greenbelts of two kinds. In the first kind, there is legacy development within the greenbelt, as is common around London. See this example:



The greenbelt is naturally in green, the cities are the light blue circles with the large central one representing the big city, and the major transportation arteries (rail + freeway) are in black. The towns within the greenbelt are all small, because they formed along rail stops before mass motorization; the freeways were built along the preexisting transportation corridors. With mass motorization and suburbanization, more development formed right outside the greenbelt, this time consisting of towns of a variety of sizes, typically clustering near the freeways and railways for best access to the center.

The freeways in this example metro area are unlikely to be very congested. Their congestion comes from commuters into the city, and those are clustered outside the greenbelt, where development is less restricted. Freeways are widened based on the need to maintain a certain level of congestion, and in this case, this means relatively unimpeded traffic from the outside of the green belt right up until the road enters the big city. Under free development, there would be more suburbs closer to the city, and the freeway would be more congested there; travel times from outside the greenbelt would be longer, but more people would live closer to the center, so it would be a wash.

In contrast, the trains are still going to be slowed down by the intermediate stops. The small grandfathered suburbs have no chance of generating the rail traffic of larger suburbs or of in-city stops, but they still typically generate enough that shutting them down to speed traffic is unjustified, to say nothing of politically impossible. (House prices in the greenbelt are likely to be very high because of the tight restrictions, so the commuters there are rich people with clout.) What’s more, frequency is unlikely to be high, since demand from within the greenbelt is so weak. Under free development, there might still be more stops, but not very many – the additional traffic generated by more development in those suburbs would just lead to more ridership per stop, supporting higher frequency and thus making the service better rather than worse.

Let us now look at another greenbelt, without grandfathered suburbs, which is more common in Canada. This is the same map as before, with the in-greenbelt suburbs removed:


In theory, this suburban paradigm lets both trains and cars cruise through the unbuilt area. Overall commutes are longer because of the considerable extra distance traveled, but this distance is traversed at high speed by any mode; 120 km/h is eminently achievable.

In practice, why would there be a modern commuter line on any of these arteries? Commuter rail modernization is historically a piecemeal program, proceeding line by line, prioritizing the highest-trafficked corridors. In Paris, the first commuter line to be turned over to the Metro for operation compatible with city transit, the Ligne de Sceaux, has continuous urban development for nearly its entire length; a lightly-trafficked outer edge was abandoned shortly after the rest of the line was electrified in 1938. If the greenbelt was set up before there was significant suburbanization in the restricted area, it is unlikely that there would have been any reason to invest in a regional rail line; at most there may be a strong intercity line, but then retrofitting it to include slower regional traffic is expensive. Nor is there any case for extending a high-performing urban transit line to or beyond a greenbelt. Parts of Grand Paris Express, namely Lines 14 and 11, are extended from city center outward. In contrast, in London, where the greenbelt reduces density in the suburbs, high investment into regional rail focuses on constructing city-center tunnels in Crossrail and Crossrail 2 and connecting legacy lines to them. In cities that do not even have the amount of suburban development of the counties surrounding London, there is even less justification for constructing new transit.

Now, you may ask, if there’s no demand for new urban transit lines, why is there demand for new highways? After all, if there was not much regional travel into these suburbs historically, why would there be enough car traffic to justify high investment into roads? The answer is that at low levels of traffic, it’s much cheaper to build a road than to build and operate a railway. This example city has no traffic generators in the greenbelt, except perhaps parks, so roads are cheap to build and have few to no grade crossings to begin with, making it easier to turn them into full freeways. The now-dead blog Keep Houston Houston made this point regarding a freeway in Portland, which was originally built as an arterial road in a narrow valley and had few at-grade intersections to be removed. At high levels of demand, the ability to move the same number of people on two tracks as on fourteen lanes of freeway makes transit much more efficient, but at low demand levels, rail still needs two tracks or at least one with passing sidings, and high-speed roads need four lanes and in some cases only two.

The overall picture in which transit has an advantage over cars at high levels of density is why high levels of low-density sprawl are correlated with low transit usage. But I stress that even independently of sprawl, greenbelts are good for cars and bad for transit. A greenbelt with legacy railway suburbs is going to feature trains going at the normal speed of a major metro area, and cars going at the speed of a more spread out and less populated region. Even a greenbelt without development is good urban geography for cars and bad one for transit.

As a single exception, consider what happens when a greenbelt is reserved between two major nodes. In that specific case, an intercity line can more easily be repurposed for commuting purposes. The Providence Line is a good example: while there’s no formal greenbelt, tight zoning restrictions in New England even in the suburbs lead to very low density between Boston and Providence, which is nonetheless served by good infrastructure thanks to the strength of intercity rail travel. The MBTA does not make good use of this infrastructure, but that’s beside the point: there’s already a high-speed electrified commuter line between the two cities, with widely spaced intermediate stops allowing for high average speeds even on stopping trains and overtakes that are not too onerous; see posts of mine here and here. What’s more, intercity trains can be and are used for commutes from Providence to Boston. For an analogous example with a true greenbelt, Milton Keynes plays a role similar to Providence to London’s Boston.

However, this exception is uncommon. There aren’t enough Milton Keyneses on the main intercity lines to London, or Providences on the MBTA, to make it possible for enough transit users to suburbanize. In cities with contiguous urban development, such as Paris, it’s easier. The result of a greenbelt is that people who do not live in the constrained urban core are compelled to drive and have poor public transportation options. Once they drive, they have an incentive to use the car for more trips, creating more sprawl. This way, the greenbelt, a policy that is intended to curb sprawl and protect the environment, produces the exact opposite results: more driving, more long-distance commuting, a larger urban footprint far from the core.

Modeling Anchoring

Jarrett Walker has repeatedly called transit agencies and city zoning commissions to engage in anchoring: this means designing the city so that transit routes connect two dense centers, with less intense activity between them. For example, he gives Vancouver’s core east-west buses, which connect UBC with dense transit-oriented development on the Expo Line, with some extra activity at the Canada Line and less intense development in between; Vancouver has adopted his ideas, as seen on PDF-page 15 of a network design primer by Translink. In 2013, I criticized this in two posts, making an empirical argument comparing Vancouver’s east-west buses with its north-south buses, which are not so anchored. Jarrett considers the idea that anchoring is more efficient to be a geometric fact, and compared my empirical argument to trying to empirically compute the decimal expansion pi to be something other than 3.1415629… I promised that I would explain my criticism in more formal mathematical terms. Somewhat belatedly, I would like to explain.

First, as a general note, mathematics proves theorems about mathematics, and not about the world. My papers, and those of the other people in the field, have proven results about mathematical structures. For example, we can prove that an equation has solutions, or does not have any solutions. As soon as we try to talk about the real world, we stop doing pure math, and begin doing modeling. In some cases, the models use advanced math, and not just experiments: for example, superstring theory involves research-level math, with theorems of similar complexity to those of pure math. In other cases, the models use simpler math, and the chief difficulty is in empirical calibration: for example, transit ridership models involve relatively simple formulas (for example, the transfer penalty is a pair of numbers, as I explain here), but figuring out the numbers takes a lot of work.

With that in mind, let us model anchoring. Let us also be completely explicit about all the assumptions in our model. The city we will build will be much simpler than a real city, but it will still contain residences, jobs, and commuters. We will not deal with transfers; neither does the mental model Jarrett and TransLink use in arguing for anchoring (see PDF-p. 15 in the primer above again to see the thinking). For us, the city consists of a single line, going from west to east. The west is labeled 0, the east is labeled 1, and everything in between is labeled by numbers between 0 and 1. The city’s total population density is 1: this means that when we graph population density on the y-axis in terms of location on the x-axis, the total area under the curve is 1. Don’t worry too much about scaling – the units are all relative anyway.

Let us now graph three possible distributions of population density: uniform (A), center-dominant (B), and anchored (C).

cityA cityBcityC

Let us make one further assumption, for now: the distributions of residences and jobs are the same, and independent. In city (A), this means that jobs are uniformly distributed from 0 to 1, like residences, and a person who lives at any point x is equally likely to work at any point from 0 to 1, and is no more likely to work near x than anyone else. In city (B), this means that people are most likely to work at point 0.5, both if they live there and if they live near 0 or 1; in city (C), this means that people are most likely to work at 0 or 1, and that people who live at 0 are equally likely to work near 0 and near 1.

Finally, let us assume that there is no modal splitting and no induced demand: every employed person in the city rides the bus, exactly once a day in each direction, once going to work and once going back home, regardless of where they live and work. Nor do people shift their choice of when to work based on the network: everyone goes to work in the morning peak and comes back in the afternoon peak.

With these assumptions in mind, let us compute how crowded the buses will be. Because all three cities are symmetric, I am only going to show morning peak buses, and only in the eastbound direction. I will derive an exact formula in city (A), and simply state what the formulas are in the other two cities.

In city (A), at point x, the number of people who ride the eastbound morning buses equals the number of people who live to the west of x and work to the right of x. Because the population and job distributions are uniform, the proportion of people who live west of x is x, and the proportion of people who work east of x is 1-x. The population and job distributions are assumed independent, so the total crowding is x(1-x). Don’t worry too much about scaling again – it’s in relative units, where 1 means every single person in the city is riding the bus in that direction at that time. The formula y = x(1-x) has a peak when x = 0.5, and then y = 0.25. In cities (B) and (C), the formulas are:

(B): y = \begin{cases}2x^2(1 - 2x^2) & \mbox{ if } x \leq 1/2\\ 2(1-x)^2(1 - 2(1-x)^2) & \mbox{ if } x > 1/2\end{cases}

(C): y = \begin{cases}(2x-2x^2)(1 - 2x + 2x^2) & \mbox{ if } x \leq 1/2\\ (2(1-x)-2(1-x)^2)(1 - 2(1-x) + 2(1-x)^2) & \mbox{ if } x > 1/2\end{cases}

Here are their graphs:

cityAcrowd cityBcrowd cityCcrowd

Now, city B’s buses are almost completely empty when x < 0.25 or x > 0.75, and city C’s buses fill up faster than city A’s, so in that sense, the anchored city has more uniform bus crowding. But the point is that at equal total population and equal total transit usage, all three cities produce the exact same peak crowding: at the midpoint of the population distribution, which in our three cases is always x = 0.5, exactly a quarter of the employed population lives to the west and works to the east, and will pass through this point on public transit. Anchoring just makes the peak last longer, since people work farther from where they live and travel longer to get there. In a limiting case, in which the population density at 0 and 1 is infinite, with half the population living at 0 and half at 1, we will still get the exact same peak crowding, but it will last the entire way from 0 to 1, rather than just in the middle.

Note that there is no way to play with the population distribution to produce any different peak. As soon as we assume that jobs and residences are distributed identically, and the mode share is 100%, we will get a quarter of the population taking transit through the midpoint of the distribution.

If anything, the most efficient of the three distributions is B. This is because there’s so little ridership at the ends that it’s possible to run transit at lower frequency at the ends, overlaying a route that runs the entire way from 0 to 1 to a short-turn route from 0.25 to 0.75. Of course, cutting frequency makes service worse, but at the peak, the base frequency is sufficient. Imagine a 10-minute bus going all the way, with short-turning overlays beefing frequency to 5 minutes in the middle half. Since the same resources can more easily be distributed to providing more service in the center, city B can provide more service through the peak crowding point at the same cost, so it will actually be less crowded. This is the exact opposite of what TransLink claims, which is that city B would be overcrowded in the middle whereas city C would have full but not overcrowded buses the entire way (again, PDF-p. 15 of the primer).

In my empirical critique of anchoring, I noted that the unanchored routes actually perform better than the anchored ones in Vancouver, in the sense that they cost less per rider but also are less crowded at the peak, thanks to higher turnover. This is not an observation of the model. I will note that the differences in cost per rider are not large. The concept of turnover is not really within the model’s scope – the empirical claim is that the land use on the unanchored routes lends itself to short trips throughout the day, whereas on the anchored ones it lends itself to peak-only work trips, which produce more crowding for the same total number of riders. In my model, I’m explicitly ignoring the effect of land use on trips: there are no induced trips, just work trips at set times, with 100% mode share.

Let us now drop the assumption that jobs and residences are identically distributed. Realistically, cities have residential and commercial areas, and the model should be able to account for this. As one might expect, separation of residential and commercial uses makes the system more crowded, because travel is no longer symmetric. In fact, whereas under the assumption the peak crowding is always exactly a quarter of the population, if we drop the assumption the peak crowding is at a minimum a quarter, but can grow up to the entire population.

Consider the following cities, (D), (E), and (F). I am going to choose units so that the total residential density is 1/2 and so is the total job density, so combined they equal 1. City (D) has a CBD on one side and residences on the other, city (E) has a CBD in the center and residences on both sides, and city (F) is partially mixed-use, with a CBD in the center and residences both in the center and outside of it. Residences are in white, jobs are in dark gray, and the overlap between residences and jobs in city (F) is in light gray.

cityD cityE cityF

We again measure crowding on eastbound morning transit. We need to do some rescaling here, again letting 1 represent all workers in the city passing through the same point in the same direction. Without computing, we can tell that in city (D), at the point where the residential area meets the commercial area, which in this case is x = 0.75, the crowding level is 1: everyone lives to the west of this point and works to its east and must commute past it. Westbound morning traffic, in contrast, is zero. City (E) is symmetric, with peak crowding at 0.5, at the entry to the CBD from the west, in this case x = 0.375. City (F) has crowding linearly growing to 0.375 at the entry to the CBD, and then decreasing as passengers start to get off. The formula for eastbound crowding is,

(F): y = \begin{cases}x & \mbox{ if } x < 3/8\\ x(5/2 - 4x) & \mbox{ if } 3/8 \leq x \leq 5/8\\ 0 & \mbox{ if } x > 5/8\end{cases}

cityDcrowd cityEcrowd cityFcrowd

In city (F), the quarter of the population that lives in the CBD simply does not count for transit crowding. The reason is that, with the CBD occupying the central quarter of the city, at any point from x = 0.375 east, there are more people who live to the west of the CBD getting off than people living within the CBD getting on. This observation remains true down to when (for a symmetric city) a third of the population lives inside the CBD.

In city (B), it’s possible to use the fact that transit runs empty near the edges to run less service near the edges than in the center. Unfortunately, it is not possible to use the same trick in cities (E) and (F), not with conventional urban transit. The eastbound morning service is empty east of the CBD, but the westbound morning service fills up; east of the CBD, the westbound service is empty and the eastbound service fills up. If service has to be symmetric, for example if buses and trains run back and forth and make many trips during a single peak period, then it is not possible to short-turn eastbound service at the eastern edge of the CBD. In contrast, if it is possible to park service in the center, then it is possible to short-turn service and economize: examples include highway capacity for cars, since bridges can have peak-direction lanes, but also some peaky commuter buses and trains, which make a single trip into the CBD per vehicle in the morning, park there, and then make a single trip back in the afternoon. Transit cities relies on services that go back and forth rather than parking in the CBD, so such economies do not work well for them.

A corollary of the last observation is that mixed uses are better for transit than for cars. Cars can park in the CBD, so for them, it’s fine if the travel demand graph looks like that of city (E). Roads and bridges are designed to be narrower in the outskirts of the region and wider near the CBD, and peak-direction lanes can ensure efficient utilization of capacity. In contrast, buses and rapid transit trains have to circulate; to achieve comparable peak crowding, city (E) requires twice as much service as perfect mixed-use cities.

The upshot of this model is that the land use that best supports efficient use of public transit is mixed use. Since all rich cities have CBDs, they should work on encouraging more residential land uses in the center and more commercial uses outside the center, and not worry about the underlying distribution of combined residential and job density. Since CBDs are usually almost exclusively commercial, any additional people living in the center will not add to transit crowding, even as they ride transit to work and pay fares. In contrast, anchoring does not have any effect on peak crowding, and on the margins makes it worse in the sense that the maximum crowding level lasts longer. This implies that the current planning strategy in Vancouver should be changed from encouraging anchoring to fill trains and buses for longer to encouraging more residential growth Downtown and in other commercial centers and more commercial growth at suitable nodes outside the center.

Penn Station Elimination Followup

Several commenters, both here and on Streetsblog, have raised a number of points about my proposal to eliminate above-ground Penn Station and reduce the station to a hole in the ground. A few of those points are things I’d already thought about when I wrote that post and didn’t want to clutter; others are new ideas that I’ve had to wrestle with.


On Streetsblog, Mark Walker says, “Getting on a train at Penn is not like using the subway. Instead of a train that runs every five minutes, you’re waiting for a train that runs once per hour (more or less),” implying nicer waiting areas and lounges are needed. My proposal, of course, does not have dedicated waiting areas. (That said, there’s an immense amount of space on the platforms under the escalators, which could be equipped with chairs, tables, and newsstands.)

However, I take exception to the notion that when the train runs every hour, passengers wait an hour. When I lived in Providence, a few trips to Boston, New Haven, and New York taught me the exact amount of time it’d take me to walk from my apartment to the train station: 21 minutes. I learned to time myself to get to the station 2 minutes before the train would leave, and as I recall, I missed the train twice out of maybe 30 trips, and one of those was when I had a lot of luggage and was in a taxi and couldn’t precisely gauge the extra travel time. Walking is that reliable. People who get to Penn Station by subway have to budget some extra time to account for missed subway trains, but from much of the city, including the parts of the CBD not within walking distance from Penn, the required spare time is less than 10 minutes. Moreover, Penn is at its most crowded at rush hour, which is precisely when subway frequency is the highest, and people can reliably time themselves to within less than 5 minutes.

Outlying train stations in Switzerland are deserted except a few minutes before a train shows up, because the connecting transit is all timed to meet the train. This is of course inapplicable at very large stations with many lines, but the modes of transportation that most Penn Station users take to the station are reliable and frequent, if you can even talk of frequency for walking. The result is that the amenities do not need to be extravagant on account of waiting passengers, and do not need to be more than those of a busy subway station in a busy area.


Several commenters raised the idea of shelter. One option, raised by James Sinclair, is an arched glass roof over the station, on the model of Milan. This involves above-ground infrastructure, but the arched structure is only supported at the margins of the compound, which means that the primary feature of a hole-in-the-ground station, the lack of anything that the track area must support the weight of, is still true. I do not think it’s a bad idea; I do, however, want to raise three additional options:

Do nothing. A large proportion of the usable area of the platforms would be located under the walkways above, or under the escalators and staircases. Having measured the depth more precisely, through Plate 14 here, I found it is 13 meters from street level to top of rail, or 12 from street level to platform level, translating to 21 meters of escalator length, plus 2.2-2.5 meters on each side for approach (see page 23 here). About 16 of those 21 (18.5 out of 25.7, counting approaches) meters offer enough space for passengers to stand below the escalators, leading to large areas that could be used for shelter, as noted in the waiting section above.

Build a simple shelter. Stockholm-area train stations have cheap corrugated metal roofs over most of the length of their platforms. These provide protection from rain. Of course those roofs require some structural support at the platform, but because they’re not supposed to hold anything except rainwater, those supports are narrow poles, easy to move around if the station is reconfigured.

Build a street-level glass pane. This may be structurally intricate, but if not, it would provide complete shelter from the elements on the track level, greatly improve passenger circulation, and create a new public plaza. But in summer, the station would be a greenhouse, requiring additional air conditioning.

Note that doing nothing or building a simple shelter would not protect any of the track level from heat or cold. This is fine: evidently, open-air stations are the norm both in cities with hotter summers than New York (Milan is one example, and Tokyo is another) and in cities with colder winters (for example, Stockholm). Passengers are usually dressed for the weather anyway, especially if they’re planning on walking to work from Penn or from the subway station they’re connecting to.


Multiple commenters have said that public art and architecture matter, and building spartan train stations is unaesthetic, representing public squalor. I agree! I don’t think a hole-in-the-wall Penn Station has to be drab or brutalist. It can showcase art, on the model of the mosaics on the subway, or the sculptures on the T-Bana. It can use color to create a more welcoming environment than the monotonous gray of many postwar creations, such as the Washington Metro. The natural sunlight would help a lot.

But more than that, the walkways themselves could be architectural signatures. The best way to build them without supporting them on the track level is some variant on the arch bridge – either the classical arch bridge (which would require three or four spans), or a through-arch. This gives a lot of room to turn the bridges into signature spans. The design work would raise their cost, but short pedestrian bridges tend not to display the same cost structure as massive vehicular ones; the Bridge of Strings, a Calatrava-designed light rail bridge on a line that cost far more to build than light rail should cost, was $70 million for 360 meters. The walkways would not carry light rail, and would be about 140 or 150 meters in span.


Commenters both here (Caelestor) and on Streetsblog (Bolwerk, Matthias, C2check) have brought up transit-oriented development as a reason to allow a tall building on top of the station. With respect, I think on top of a train station is exactly the wrong place to build a tower. Let’s Go LA has an explanation for why the engineering for air rights is so complicated, although he stresses that Penn Station and Grand Central, which were built with the expectation of future high-rise air rights, are exceptions. I’ll add that Penn Station track simplification would also remove many crossovers and switches, making it easier to build air rights. That said, the track spacing is not friendly to the column spacing he proposes.

In New York, the tallest and most expensive recent private-sector office tower on solid ground, the Bank of America Tower, cost around $6,000 per square meter of floor space, in today’s money. Some of the luxury residential towers are more expensive; so are the new World Trade Center buildings, e.g. One World Trade Center was $12,000 per m^2. But the office towers cluster in a specific band of cost, around $2,500 to $5,000 per square meter, with taller towers generally more expensive. The Hudson Yards air rights towers cost in the $10,000-14,000 per square meter range, as much as One World Trade Center. Contrary to Bloomberg’s promises of windfall property tax revenues as his justification for the 7 extension, the city has had to offer tax abatement to encourage developers to build at those prices. Amtrak’s plan for Penn Station South assumes the block immediately south of Penn Station would cost $769 million to $1.3 billion to acquire; when I roughly computed its floor area by counting floors per building, I got 100,000 m^2, which means the price of real estate in that area, $7,700-13,000/m^2, is no higher and may be lower than the construction cost of air rights towers.

In contrast, some sites on firm ground immediately surrounding Penn Station are ripe for redevelopment. The block south of Penn Station, as noted above, has about 100,000 m^2, for a block-wide floor area ratio of 6.7. The Empire State Building’s floor area ratio is 33, so replacing the block with closely spaced supertall towers would require developers to burn just 20% of their profit on acquiring preexisting buildings. To the north of Penn Station, the two sites at 7th and 8th Avenues, flanking One Penn Plaza, are flat; so is nearly all of the western part of the block northeast of Penn, between 33rd and 34th Streets and 6th and 7th Avenues. Eighth Avenue is not developed intensely at all in that latitude – it only becomes important near Times Square. Supertall buildings surrounding Penn Station could even be incorporated into the station complex: railroads using the station might decide to lease offices in some of them, and the exteriors of some of those buildings could incorporate large clocks, some signage, and even train departure boards.


TheEconomist, who has had some truly out-of-the-box ideas, raises a very good point: how to phase the deconstruction of Penn Station in ways that allow service to continue. I don’t have a complete answer to that. Arch bridges, in particular, require extensive falsework, which may complicate matters. However, a general phase plan could consist of knocking down the above-ground buildings, then removing the upper concourse (leaving only the lower), and then removing arms of the lower concourse one by one as the walkways above them are built.

Passenger Throughput

In comments here, people have suggested several alternatives to my proposal to reconfigure Penn Station to have 12 tracks and 6 island platforms between them. There should be 6 approach tracks, as I outlined here: southern approach tracks, combining new Hudson tunnels with a link to Grand Central (which I call Line 2); central tracks, combining the preexisting Hudson tunnels with the southern East River Tunnels (Line 1); and northern tracks, combining the realigned Empire Connection and West Side Yard with the northern East River Tunnels (Line 3).

In my view, each approach track should split into two platform tracks, flanking the same platform. In this situation, there is no need to announce track numbers in advance, as long as the platform is known. Stockholm does this on the commuter lines at Stockholm Central: the northbound lines use tracks 15 and 16 and the southbound lines use tracks 13 and 14, with a platform between each of these track pairs, and until a few minutes before a train arrives, it’s signed on the board as “track 13/14” or “track 15/16.”

The compound looks 140 or 150 meters wide; the maps are unclear about to what extent Penn extends under 31st and 33rd, but according to a diagram Joey shared in comments, it extends quite far, giving 150 meters or even a bit more. Under my proposal, this is enough for 6 platforms of 17 or 18 meters. It sounds like a lot, but it isn’t, especially on Line 3, where Penn Station is the only CBD train station, which implies entire trains would empty at Penn in the morning rush hour. (Line 2, which I expect to be the busiest overall because it’d serve both Penn and Grand Central, is the one I expect to have the least platform crowding problems, precisely because it’d serve both Penn and Grand Central.)

Staircases should be 3 meters wide. Escalators with 1-meter steps have 1.6-meter pits; their capacity is theoretically 9,000 passengers per hour, but practically only 6,000-7,000. Clearing 30 entire trains per hour, filled to seating capacity with 4 standees per square meter of standing space, requires moving about 75,000 passengers per hour. (Per meter of train length, this is comparable to the 4/5 trains and the RER A at their peaks.) With 6 access points, this requires 2 up escalators per access point. The minimum is then 3 escalators, running 2-and-1 at the peak; 4 is better.

In comments, Ari Ofesvit proposes the Spanish solution, which I’ve discussed in previous posts. I’m now convinced it is not the right solution, simply because it compels platforms to be too narrow (about 8.6 meters), which has room for exactly half of what a standard platform twice the width would have, without the possibility of running 4 escalators 3-and-1 at the peak. My comment in that post has more detail, albeit with the assumption that the compound is 140 meters wide.

Fbfree proposes something else: more platforms for intercity trains. Giving intercity trains more platforms (as is done in Stockholm, which has just two approach tracks to the south) gives them more time to dwell; unfortunately, it also narrows the platforms for the regional trains, precisely the ones that can expect the most crowding. Even a single-track platform would take up space out of proportion to the number of passengers it would serve.

Pedestrian throughput is, at the maximum, 81 people per meter of walkway width per minute; this assumes two-way flow, but the numbers for one-way and multiway flow aren’t too different. This is a little less than 5,000 per meter-hour. An escalator bank with two up escalators then needs almost 3 meters of unobstructed platform width on one side (the other side can be used as overflow, but most passengers would use the side of the platform the train discharged them on). This is easy to supply with a 4-escalator bank on a 17-meter platform (there would be 3.8 meters); on an 8.6-meter Spanish platform, there’s only one up escalator per bank, so half the width is required, and is indeed obtainable. But if there are extra platforms for intercity trains, this becomes more strained.

For maximum throughput, it is necessary to minimize separation between escalators on the platform, down to about 6 meters plus approaches, in order to allow wider walkways, which in this case would make the walkways about 25 meters wide. The point here is that the walkways have to have very high pedestrian capacity, since each of them is fed by escalators from all platforms. At 25 meters, the capacity is about 15% less than that of two up escalators per access point (121,500 vs. 144,000), which is fine since some platforms (Line 2 in both directions, Line 3 eastbound in the morning and westbound in the afternoon) would not have so much traffic. But putting in elevators would disrupt this flow somewhat.

I see two ways to increase capacity in the future, if train traffic warrants it: first, build the glass floor/ceiling I outlined above, in the shelter section. This is the simplest possibility. Second, build three more walkways, midway between 7th and 8th Avenues and the two walkways already discussed, and have each walkway or avenue serve only half the platforms – one serving eastbound platforms, one serving westbound platforms. At this point the station would be half-covered by walkways, if they are all about 24 meters wide, but the walkways could be narrowed; as long as they are longer than 15 meters, any passenger arriving on a platform by any of the included access points would be sheltered by the walkway serving platforms in the opposite direction. Elevators should go from each walkway to each platform still, which would facilitate transfers, but the workhorse escalators would spread the load among different walkways.


I’d originally thought that the walkways could host retail and food concessions. The calculation in the preceding section suggests that this wouldn’t be possible, unless the walkways are widened beyond the escalators, with concessions on the outside. Every meter of walkway width would be required for passenger circulation. Even information pamphlets might be restricted to the very edges of the walkways; train departure boards would have to be mounted in the air, for example on the support cables if the through-arch option were chosen for the walkways.

However, there is ample room directly beneath the escalators, staircases, and walkways. With the caveat that escalators of such length need an extra midway support point, they would still have a lot of space underneath: 15-16 meters with sufficient clearance for people to stand comfortably (say, at least 2.5 meters of clearance above); with the upper approaches and the walkways, this is 60-62 meters of largely unobstructed space, for a 60*10 space that could be used in almost any way. Even in the 5-6 meters with less clearance above to the escalator, it’d be possible to use the space at least partly – for example, for sitting, or for bathrooms, the minimum clearance is reduced (I’m writing this post from my apartment, where the ceilings slope down, and the ceiling height above my couch is about 1.5 meters).

There would be two such 60*10 spaces per platform, plus two smaller spaces, near 7th and 8th Avenues, depending on exact placement of access points to the subway. This gives us twelve 60*10 spaces. I doubt that they could ever host high-end concessions, such as full-service restaurants: passengers would probably not go out of their way, to a platform that they weren’t planning on using. This means newsstands could succeed, but not much else; food would have to be shunted to the streets, and presumably restaurants would pay extra to locate right outside the compound. In lieu of concessions, those spaces could host sundry uses, including additional circulation space, information pamphlets, busker performance space, waiting areas for passengers, public art displays, and waiting areas for train crew and cleaners.

The Ultimate Authoritarian Anti-Urbanism

Cairo is a dense megacity, without the infrastructure such cities require for high living standards. The city proper, according to Wikipedia, has 10 million people, living at a density approaching 20,000 per km^2, and the metro area has 20 million. With a subway system fit for a city a tenth its size, Cairo is heavily motorized for its income level, congested, and polluted. Despite high construction costs, urgent investment in public transportation is required. Ignoring this need, the current military government has just announced plans to build a new capital outside the city, eventually to house 7 million people, with all the public monuments of a planned city, at a cost of $300 billion (exchange rate dollars, not PPP), about the same as Egypt’s annual GDP. The first phase alone will be $45 billion.

Cairo itself is already suffering from neglect and disinvestment. There are 2 million cars in the city. This is enough to cause so much traffic congestion it costs Egypt 4% of its GDP. Cairo’s air pollution is legendary: pollution levels are akin to smoking a pack of cigarettes per day. At least as of 1997, lead pollution caused by cars using leaded gasoline reduced Cairene children’s IQ by 4 points. The poor transportation options have led to a housing crunch, forcing half a million people to live in a historic necropolis as squatters.

The Cairo Metro would be a solution to these problems to a large extent, but is very small relative to Cairo’s size: it has 3 lines, totaling 78 route-km. Other cities of comparable size have many hundreds of route-km of urban rail, with a handful of exceptions infamous for their sprawl (such as Los Angeles) or pollution (such as Sao Paulo). Despite its small size, the Cairo Metro gets about 1.6 billion passengers per year, by far the highest number of passengers per route-km in the world, nearly twice as high as on the legendarily overcrowded Tokyo subway. Cairo has high construction costs, but in exchange rate dollars they only amount to about $130 million per km; a fully underground expansion of the subway to 400 km, somewhat more than the length of New York’s subway lines and less than that of Beijing and Shanghai’s, would cost about $40 billion, less than the cost of the new capital’s first phase alone. This is on top of all other possible infrastructure investments Egypt should consider: sanitation, sewage, water treatment, electrification, hospitals, schools, the Suez Canal. I bring up the Metro since so many of Cairo’s pressing problems would be substantially reduced if it had the capacity to transport a large share of the city’s population.

The problem is that the Egyptian government’s first priority is not to serve the needs of the Egyptian population. It is an authoritarian military government; it is not accountable to the broad public. I bring this up, because it’s a necessary check on things I have said in the past, attacking local American governance as authoritarian. Andrew Cuomo and Chris Christie have the power to overrule useful spending bills and cause traffic jams in cities run by political opponents. Abdel Fattah al-Sisi has the power to jail political opponents without trial, and execute them by the hundreds after show trials.

Autocrats love planned cities, for two reasons. First, planned cities are monuments to their greatness, lasting long into the future. The people the autocrats trample will be forgotten. Tourists visit the Taj Mahal, and not museums commemorating the churches and temples Shah Jahan destroyed. They visit the Great Wall of China, and not any commemoration of the million-odd people who died in its construction. They visit the Old City of Jerusalem, while nobody commemorates any of the locals Herod taxed to build its monuments – even Judaism only commemorates the destruction of the Temple and the beginning of the Diaspora, generations later. Autocrats know this. Even in antiquity, they knew monuments would make them more famous. And even in modern democratic regimes, politicians like signature initiatives that have their names on them; going back to Andrew Cuomo, his proposed Queens convention center is a typical example. But Cuomo still faces some democratic checks and balances. Sisi does not.

And second, planned cities can be built in ways that enhance social control. City Metric compares the new planned capital with Naypyidaw, Burma’s capital, built in the era of military rule to replace Yangon. Purpose-built capitals can be (and are) built around the needs of the national elite, keeping the poor out of sight. They have street and building design plans that make it easy to bring in the military to quell riots: wide streets, buildings that do not touch, no central square where protests could happen. They also disallow squatters, without going through the difficult and controversial move of evicting squatters from the preexisting city. One rhetorical question I have seen on Twitter is, where will this city’s Tahrir be? An article on Cairobserver doesn’t make this exact argument, but does note that this plan disinvests in what will still remain Egypt’s largest city, and could only come about as a result of Egypt’s complete lack of democracy.

One of the bigger influences on my views of democracy is Brad DeLong and Andrei Shleifer’s paper from 1993, Princes and Merchants. I do not fully agree with the point they make, but one of the key components of it, on the spending priorities of an absolute ruler, is crucial to understanding the benefits of democracy. Per DeLong and Shleifer, absolutism chokes economic growth, since the absolute ruler will overtax the economy to maximize revenue. One may ask if actually, hereditary rulers would want to stimulate more economic growth in order to bequeath a stronger kingdom to their heirs. DeLong and Shleifer answer that no: even with clear rules of inheritance, succession wars are so common that kings have to constantly be on the guard against rebellion to make sure their heirs get to inherit anything.

For Sisi, it is perfectly rational to spend so much money building a capital city that would make an uprising against him less likely. The money is not going to come from his pocket, but from the pockets of people he need not care about too much – the Egyptian people. The personal benefits to Sisi are invaluable: Sisi’s two predecessors, Mohamed Morsi and Hosni Mubarak, were both overthrown and immediately charged with crimes, for which they were guilty (under Sisi’s influence, Mubarak was exonerated from most). Why not remove himself and the apparatus of the Egyptian state from the city where they were overthrown?

When I talk of infrastructure democracy in democratic first-world countries, I complain about (much) smaller versions of this exercise. One could reason with a democratic Egyptian government that there are better uses of the money in Cairo itself. One cannot reason this way with a military government. The same is true of the soft authoritarianism found in governments with a democratic deficit, from the European Commission to local American governments. Their power is ultimately limited by other layers of government, which are more transparent, and they are incapable of killing off political opponents, but they still do not have to listen to the people they impact, leading to decisions that are at times obviously ridiculous. Egypt’s new capital is this autocracy, taken to its logical end. A dictator, of the kind who the infrastructurists might praise as someone who can cut through the red tape and gets things done, is spending the country’s annual GDP on a plan to disinvest in the capital and build a monument to himself and his regime from scratch.

Height Limits: Still a Bad Idea

In a pair of recent articles on Strong Towns, Charles Marohn, best known in the urbanist community for introducing the term stroad (street+road) for a pedestrian-hostile arterial street, argues for height limits as a positive force for urbanism. He does not make the usual aesthetic argument that tall buildings are inherently unpleasant (“out of scale”), or the usual urbanist one that tall buildings lead to neighborhood decline; instead, he makes an economic argument that allowing tall buildings greatly raises land costs, and makes redevelopment of vacant lots less likely. He uses the following example:

Let’s say the local code allows [a] vacant lot to be developed as a one story strip mall, but nothing higher. If the strip mall is worth $500,000, then the vacant lot is going to be somewhere around $75,000.

Okay, but what if the development code allows that vacant lot to be developed as a sixteen story tower? If the tower is worth $20,000,000, then that vacant lot is going to fetch a much higher price, maybe as much $2.5 million.

You own that vacant lot. I come to you with an offer to buy it for $75,000. What are the odds you are going to sell it at that price when you look to the other side and see the same piece of property going for millions? Not very good.

In most cities, as Charles notes, there is not enough demand to redevelop every vacant lot as a high-rise, and therefore, if high-rises are permitted, a few vacant lots will be redeveloped as high-rises, while the rest remain vacant. This is not the case in large cities, which Charles specifically exempts in his article (see also Daniel Kay Hertz’s response), but part of the problem with the argument, as we will see, is that the boundary between large cities and small ones is fuzzy.

Let me now explain why this argument fails, like all the other arguments for zoning restrictions: it makes implicit assumptions on future uncertainty. The reason the vacant lot owners are not willing to sell for $75,000 is that they hope to get $2.5 million. In a stable market, with low enough population that most lots cannot fetch such a high price, the lot owners know that holding off on $75,000 offers is a gamble and that they are unlikely to ever get a higher offer. People have optimism bias and might overrate the probability that they’ll get the $2.5 million offer, but also have risk aversion; in most cases in economics, risk aversion dominates, so that safer assets cost more and have lower returns.

So when do we see holdouts? Risk aversion predicts that the probability of obtaining a $2.5 million offer should be higher than the total demand for new towers divided by the number of vacant lots. If we explicitly assume that the cost figures in Charles’ example, including land costs, are unchangeable, then this means vacant lot owners expect there to be more high-rise towers in the future, which comes out of growth regions. Charles’ example is based on Sarasota, which like most of Florida has high population growth.

The other possibility is regulatory uncertainty. In a competitive market, land costs are already as low as they can be while letting lot owners cash out on past investments. Developer profits are also as low as possible, and represent the developer’s wage for managerial work. However, zoning restrictions will greatly raise both figures, and a lot owner who expects future developments to brush up against the present zoning code can hold out until prices rise.

This is the danger of a system that is based on arbitrary rules (Charles proposes up to two floors or 1.5 times the average present height, whichever is higher), and arbitrary distinctions between small cities in which height restrictions are desirable and large cities in which they are not: these introduce political discretion in the details, which introduces additional uncertainty among lot owners. True windfalls usually involve the boundary between regulatory regimes, and this creates political incentive to game the system in order to be one of the few owners whose lots can be developed as high-rises. In contrast, once a ground rule is established that there is no zoning, such as in Houston, introducing zoning is difficult, even when there are rules that are zoning in all but name, such as parking minimums.

Once we get into the realm of cities with a large proportion of their lots developed, as Charles proposes, future development can only replace old development, and this introduces a key difference between new development and redevelopment: redevelopment requires buying out the preexisting property. If a two-floor building is replaced by a three-floor building, then the developer has to not only pay construction costs for three floors, but also buy out two floors, effectively paying for five floors. But the revenue is still only that of a three-floor building, which bids up effective costs by a factor of five thirds. The formula is that if it’s possible to multiply the total built-up area by a factor of x then the buy-out factor will raise the cost of each housing unit by a factor of 1 + 1/x.

This effect is why, in major cities, we usually see buildings replaced by much larger buildings: for example, a three- or four-floor Manhattan building may be replaced by a fifteen- or twenty-story tower on a base. Charles laments that this is not small-scale or incremental, but even his example of good incremental development is similar: in Houston, single-family houses are replaced by low-rise apartment buildings, generating similarly high ratios of the floor areas of redevelopments with the buildings they replaced. Incrementalism in these cases consists of replacing small buildings by much larger ones, gradually, until a few decades later the entire neighborhood is tall.

One way around redevelopment’s need to buy out preexisting buildings is to mandate that future buildings be built to allow adding floors on top of them. Chicago’s Blue Cross Blue Shield Tower is an example. This is a regulation that increases the average cost of construction but reduces the marginal cost and thus the price. It’s also a regulation that only really matters in situations when it is difficult to have a high ratio of new to old floor area, such as in areas that are already high-rise, especially major city CBDs. (It is easy to quintuple floor area ratio when the preexisting buildings have three floors, but not so much when they have twelve.) The current styles of construction of most small buildings, for example sloping roofs common in American and European urban and suburban houses, tend to make adding floors impossible. Of course, the implication that such a regulation should only apply for buildings above a certain height introduces political discretion and hence uncertainty, but at least this is uncertainty that would apply equally to all buildings in an area, which is not always the case for zoning.

What Charles proposes, to develop all vacant lots first and only then start going taller, is then a recipe for high marginal costs, because of the buyout factor. In a small city uniformly developed up to one or two floors, it is difficult to spread the new development across many buildings up to three floors, precisely because there is no way to build single-family houses that are recognizable as such to Americans or Europeans from countries I’ve been to (It’s different in Canada, but this is considered a feature of the low quality of Vancouver’s housing) and that can have floors added to them. In such an environment, building tall is the only way to avoid high housing costs.

Pedestrian Observations from Central Stockholm

I like Stockholm. There’s something reassuringly familiar about it, despite the language barrier, which I think comes from the fact that the Central Stockholm housing stock is of similar vintage as the residential parts of Manhattan. It even avoids New York’s most annoying (to me) architectural tic, the exposed brick. The buildings here are similar in style to the ones in New York (and more generally northern Europe), but most have smooth exterior, with enough variation of colors between buildings to make it interesting.

The streets here vary a lot in width, but outside the older sections of the city, they are never very narrow. In Gamla Stan (“the old town”), the medieval core of the city that is now a tourist ghetto, complete with stores selling Swedish flags or English-language books, there are some pedestrianized streets with single-digit building-to-building width. But in my part of the city – Roslagstull, near the outer end of what’s considered Central Stockholm – the street width ranges are almost identical to those of Manhattan. My street, Birger Jarlsgatan, is about 30 meters wide, while less important parallel streets are about 15 or 20. Like the rest of city center, it’s lined with almost uniformly mid-rise buildings, six to seven stories tall. See photos here, from Södermalm, and here, from Regeringsgatan, a street that for a portion of its length is elevated over intersecting streets.

A feature of Stockholm streets that I have not seen in other cities is that on-sidewalk bike lanes. While the overall sidewalk width on Birger Jarlsgatan is generous, the sidewalk is broken by the bike lane. The inner side of the bike lane is interrupted by trees, and the outer side by sidewalk cafes, and as a result, sometimes walking in the bike lane is unavoidable if one wishes to avoid walking in zigzags. In any case, cyclist traffic does not seem to be heavy; there is much more pedestrian traffic.

Crossing the street is rarely difficult. There are beg buttons at intersections, but the pedestrian light will turn green even without pressing them. The stoplight phasing is simple: most of Central Stockholm is on one of several grids, and even at intersections of two-way streets (one-way streets are uncommon, at least around Roslagstull), there are only two phases per stoplight cycle. Without grade-separated freeways in the city core, the worst streets for the pedestrians are the occasional freeway-like structure, or one of several excessively wide roads. I walk to work on one of those roads, Valhallavägen, and during the daytime, the cars’ noise and air pollution are uncomfortable unless I walk through the parking lots behind the street or the bus bay in its median.

The transit system is useful, though I almost never take it. This is a combination of very high fares (with my pay-per-ride smartcard, I pay 25 kronor per ride, about PPP$2.70) and a city core that’s small enough and pedestrian-friendly enough that I can get around most of it on foot. The pedestrian orientation of the streets matters: my apartment is 2.3 km from the CBD mall and 1.7 km from Stockholm University; but I will walk to the mall, whereas to get to and from a conference at SU, I didn’t walk on Roslagsvägen (which is almost a full freeway) but instead took the subway from my university, KTH, which is more centrally located within the city.

Of course, most people in the region don’t live in Central Stockholm, and for them the T-bana is a lifeline. Subway ridership here, excluding commuter rail, is about 900,000 per day (not weekday), not much lower than on the U-Bahns of much larger Berlin and Munich. As a curiosity, there are many light rail lines that connect outlying suburbs to a T-bana station, requiring a transfer to get to the CBD; the busiest, Roslagsbanan, is a narrow-gauge commuter rail system terminating next to KTH, with one T-bana branch, the T14, running parallel to it for a few stops before terminating. This is in addition to a mainline commuter rail system, with 267,000 daily passengers; this ratio of about one commuter rail rider to three subway riders is higher than anything most (see first two comments) in North America, but is much lower than in major European transit cities like Paris and London, where commuter rail and the metro have roughly equal ridership levels. Among the transit projects under construction in Stockholm is a new rail tunnel, which will increase the capacity of commuter rail.