Category: Urbanism

Building Depth and Window Space

How much window space does an apartment need, relative to its area, and how does this affect building style? A fascinating post from about a year ago on Urban Kchoze makes the argument that modern North American buildings are too deep – Simon calls them obese. Simon contrasts the typical building style in major cities in Europe and Asia with modern North American imitators and argues that the North American versions have too much ratio of floor area to exterior window width, which only works with loft-style apartments, which are not fit for families.

Is Simon correct? Not really. There’s an important feature of the block style in Europe that he’s missing. And this leads to an interesting observation by itself about area-to-window-width ratios.

The issue of building depth

Simon shows a bunch of satellite photos of buildings in a style called the euroblock. Here’s one example from Stockholm, in Södermalm:

The block has a width that looks like 14.6 meters. Midblock buildings have front windows overlooking the street and back windows overlooking a central courtyard; corner buildings overlook two streets. Either way, the area-to-frontage ratio is 7.3 meters. In general, buildings in Central Stockholm, urban Berlin, and Paris in average a depth of 13-14 meters, so the above typology would generate a ratio of 6.5-7 meters.

Simon contrasts this with American buildings. The euroblock typology is very uncommon in the US – New York’s typology is much less neat and liberally uses windows that overlook very narrow spaces. But it does exist, generally in higher-end recent developments. For example, here’s the Avalon East Norwalk, a condo project wedged between I-95 and the Northeast Corridor.

It has essentially the same built form as the euroblock. Its development history is of course different: there are no streets on the exterior, only parking lots, and it is a single project surrounding a big plaza with a swimming pool rather than many small buildings that together enclose a courtyard that comprises several separate gardens. But in terms of how the building looks from space, it’s similar. The width is 20 meters, for an area-to-frontage ratio of 10 meters, well above 6.5-7 meters.


Euroblocks are complicated

The above Stockholm pic is a pretty simple building, conceptually: a linear building outlining the edge of a rectangle. This is not the typical euroblock; I had to look around Central Stockholm to find a fitting example. I could equally well use Hamburg or another such city of the same size class.

But in Paris, this form is almost unheard of, and in Berlin it is uncommon, I think mostly denoting postwar reconstruction. Paris and Berlin are larger cities, especially historically – in the Belle Epoque/Wilhelmine era, when this typology flourished, they were two of the largest few cities in the world, Berlin stagnating after World War Two and Paris growing exclusively in the suburbs. So they’d build up more of each lot and leave less unbuilt space between buildings. Instead, here is what a traditional Berlin block looks like, in this case in Neukölln:

These buildings enclose a central courtyard, as in Stockholm, but there the similarity ends. The courtyard is small, and there are several to a block. All these wings have internal corners with limited window space. Moreover, the wings that do not make it all the way to enclosing the courtyard, like the ones on the buildings north of Laubestrasse, have blank walls facing northeast, because they were built expecting the wing of another building to directly abut them. The wing of the building at the Laubestrasse/Elbestrasse eastern corner likewise has blank northeast-facing walls, and from space looks awkward, like a half-building. All of this was designed for more buildings, but some were never built or were knocked down.

If the euroblock has one big courtyard for the entire block as in the Stockholm and Norwalk examples, then the area-to-frontage ratio equals exactly half the building depth. But as soon as there are multiple courtyards, the ratio grows. The dimensions of the C-shaped building on Sonnenallee (one block south of Laubestrasse) just west of the corner building with which it shares the courtyard are 18 meters of street frontage by 38 of lot depth minus a half-courtyard of 11.5*12. This works out to 546 m^2/71 m, for a total ratio of 7.7 m, even though technically the building is never deeper than 13 m.

The blocks can get even more fractured. Here’s Prenzlauer Berg, in an area wedged between the former Wall and the Ringbahn:

The dimensions of the buildings fronting Korsörer Strasse on the north are pretty consistent. They all have an overall lot depth of about 32 meters, consisting of 14 meters of building, 11 meters of courtyard, and 7 meters of half-building with blank north-facing walls. The side wings are pretty consistently 7 meters deep each as half-buildings. Taking the pair of buildings flanking the second courtyard from the east as an example, they together are 35*32 minus 21*11, for 889 m^2/99 m = 9 m.

In Paris, building forms vary. But here is an example with wings, in the 17th:

The courtyards are smaller than in Berlin. Taking the second building from the west, we get 35*25 – 11*13, or 732 m^2/98 m = 7.5 m. When the courtyard is only about as wide as the building is deep, the above typology, similar to the image from Neukölln, generates a ratio equal to 5/8 the building depth, and not 1/2 as in the Stockholm example. The Prenzlauer Berg typology generates an even higher ratio, a full 2/3 of building depth if the courtyard is a square of side equal to the building depth.

And this matters. Buildings with simpler sides do get deeper in Paris. For example, this building in the 16th, wedged between two streets:

The depth of these buildings is 18 meters, so the area-to-frontage ratio is 9 m.

What does this mean?

My choice of the 16th and 17th in Paris for my examples is not random. Western Paris has been rich from the moment it urbanized – families of means choose to live this way. In general, within the family of euroblocks, the more desirable areas seem to have buildings with a slightly larger depth – the more working-class parts, such as Eastern Paris, have shallower buildings. Rich people would all else being equal prefer more window frontage space, but all else is not equal, and they prefer bigger apartments.

There is a definite limit on how deep buildings can be and how large the ratio of area to window frontage can be, but it is not as low as Simon posits. Ratios in the 8-9 region are not unheard of in old European buildings, and it stands to reason that euroblocks built in an environment of more prosperity, such as that of the early 21st century, could go slightly higher.

Moreover, the Norwalk example of a deeper building without wings is generally preferable to the traditional Berlin and Paris form of shallower buildings with wings. In Berlin, the apartments with street-facing windows are the most desirable. Historically, the wings were for the working class, which had to make do with narrow courtyards – sometimes narrower than today, the original statutory limit being less than 6 m wide due to 19th-century fire regulations. So the evolution of the euroblock is likely to be toward its American condo form.


I recently covered the Stadtbahn, a mode of rail transportation running as rapid transit (almost always a subway) in city center and as a tramway farther out. The tram-train is the opposite kind of system: it runs as a tramway within the city, but as rapid transit farther out. There’s a Human Transit blog post about this from 2009, describing how it works in Karlsruhe, which invented this kind of service pattern. Jarrett is bearish on the tram-train in most contexts, giving a list of required patterns that he says is uncommon elsewhere. It’s worth revising this question, because while the tram-train is not very useful in an American context, it is in countries with discontinuous built-up areas, including Germany and the Netherlands but also Israel. Israeli readers may be especially interested in how this technology fits the rail network away from the Tel Aviv region.

What is a tram-train?

Let’s dredge the 2*2 table from the Stadtbahn post:

Slow in centerFast in center
Slow in outlying areasTramwayStadtbahn
Fast in outlying areasTram-trainRapid transit

The terms fast and slow are again relative to general traffic. The Paris Métro averages 25 km/h, less than some mixed-traffic buses in small cities, but it still counts as fast because the speed in destinations accessed per hour is very high.

Be aware that I am using the terms Stadtbahn and tram-train to denote two different things, but in Karlsruhe the system is locally called Stadtbahn. German cities use the term Stadtbahn to mean “a tramway that doesn’t suck,” much as American cities call a dazzling variety of distinct things light rail, including lines in all four cells of the above table. Nonetheless, in this post I am keeping my terminology distinct, using the advantage of switching between different languages and dialects.

Tram-trains and regional rail

The Karlsruhe model involves trains running on mainline track alongside mainline trains, diverging to dedicated tramway tracks in the city, to connect Karlsruhe Hauptbahnhof with city center around Marktplatz. This also includes lines that do not touch the mainline, like S2, but still run with higher-quality right-of-way separation outside city center; but most lines run on mainline rail part of the way.

North American light rail lines, with the exception of the Boston, Philadelphia, and San Francisco Stadtbahn systems, tend to run as tram-trains, but never have this regional rail tie-in. They run on entirely dedicated tracks, which has two important effects, both negative. First, it increases construction costs. And second, it means that the shape of the network is much more a skeletal tramway map than the more complicated combination of an S-Bahn and a tramway that one sees in Karlsruhe. San Diego has a short segment sharing tracks with freight with time separation, but the shape of the network isn’t any different from that of other American post-1970s light rail systems, and there’s an ongoing extension parallel to a mainline railroad that nonetheless constructs a new right-of-way.

In this sense, the Karlsruhe model can be likened to a cheaper S-Bahn. S-Bahn systems carve new right-of-way under city center to provide through-service whenever the historic city station is a terminus, such as in Frankfurt, Stuttgart, Munich, or German-inspired Philadelphia. They can also build new lines for more expansive service, higher capacity, or a better connection to city center, like the second S-Bahn trunk in Hamburg; Karlsruhe itself is building a combined road and rail tunnel, the Kombilösung, after a generation of at-grade operation. The tram-train is then a way to achieve some of the same desirable attributes but without spending money on a tunnel.

It follows that the tram-train is best when it can run on actual regional rail tracks, with good integration with the mainline system. It is a lower-speed, lower-cost version of a regional rail tunnel, whereas the North American version running on dedicated tracks is a lower-cost version of a subway. Note also that regional rail can be run at different scales, the shorter and higher-frequency end deserving the moniker S-Bahn; the Karlsruhe version is long-range, with S1 and S11 reaching 30 km south of city center and S5 reaching 70 km east.

Where is a tram-train appropriate?

Jarrett’s 2009 post lays down three criteria for when tram-trains work:

  • The travel market must be small enough that an S-Bahn tunnel is not justified.
  • The destination to be served isn’t right next to the rail mainline.
  • The destination to be served away from the mainline is so dominant that it’s worthwhile running at tramway speeds just to get there and there aren’t too many people riding the line beyond it.

The center of Karlsruhe satisfies the second and third criteria. It is borderline for the first – the region has maybe a million people, depending on definitions, and the city proper has 312,000 people; the Kombilösung is only under-construction now and was not built generations ago, unlike S-Bahn tunnels in larger cities like Munich.

Jarrett points out that in the urban world he’s most familiar with, consisting of the United States, Canada, Australia, and New Zealand, it is not common for cities to satisfy these criteria. He does list exceptions, for example Long Beach, where the Blue Line runs in tramway mode before heading into Los Angeles on a mostly grade-separated right-of-way, whereupon it goes back into the surface in Downtown LA before heading into an under-construction tunnel. But overall, this is not common. City centers tend to be near the train station, and in the United States there’s such job sprawl that just serving one downtown destination is not good enough.

That said, the Long Beach example is instructive, because it is not the primary city in its region – Los Angeles is. I went over the issue of outlying S-Bahn tunnels a year ago, specifying some places where they are appropriate in Israel. The tram-train must be a key tool in the planner’s box as a cheaper, lower-capacity, lower-speed version of the same concept, diverging from the mainline in tramway mode in order to serve a secondary center. Karlsruhe itself is a primary urban center – the only time it’s the secondary node is when it connects to Mannheim, and that train doesn’t use the tramway tracks – but a secondary tram-train connection is being built in outlying areas there, namely Heilbronn.

Different models of urban geography

In the American model of urban geography, cities are contiguous blobs. Stare at, for example, Chicago – you’ll see an enormous blob of gray stretching in all directions. Parkland is mostly patches of green in between the gray, or sometimes wedges of green alternating with wedges of gray, the gray following commuter railroads and the green lying in between. Boundaries between municipalities look completely arbitrary on a satellite map.

In the German model of urban geography, it’s different. Look at Cologne, Frankfurt, Mannheim, or Stuttgart – the built-up area is surrounded by green, and then there are various suburban towns with parkland or farmland in between. This goes even beyond the greenbelt around London – there’s real effort at keeping all these municipalities distinct.

I don’t want to give the impression that the United States is the weird one. The contiguous model in the United States is also common in France – Ile-de-France is one contiguous built-up area. That’s how despite being clearly a smaller metropolitan region than London, Paris has the larger contiguous population – see here, WUP 2007, and see also how small the German and Dutch urban areas look on that table. Urban agglomeration in democratic East Asia is contiguous as in the US and France. Canada looks rather American to me too, especially Vancouver, the city both Jarrett and I are the most familiar with, while Toronto has a greenbelt.

This distinction moreover has to be viewed as a spectrum rather than as absolutes. Boston, for example, has some of the German model in it – there’s continuous urbanization with inner suburbs like Cambridge and Newton, but beyond Route 128, there are many small secondary cities with low density between them and the primary center. Conversely, Berlin is mostly American or French; the few suburbs it has outside city limits are mostly contiguous with the city’s built-up area, with the major exception of Potsdam.

The relevance of this distinction is that in the German or Dutch model of urban geography, it’s likely that a railway will pass through a small city rather far from its center, fulfilling the second criterion in Jarrett’s post. Moreover, this model of independent podlike cities means that there is likely to be a significant core, which fulfills the third criterion. The first criterion is fulfilled whenever this is not the center of a large metropolitan area.

It’s not surprising, then, that the Karlsruhe model has spread to the Netherlands. This is not a matter of similarity in transport models: the Netherlands differs from the German-speaking world, for examples it does not have monocentric S-Bahns or S-Bahn tunnels and it builds train stations with bike parking where Germany lets people bring bikes on trains. Nonetheless, the shared model of distinct municipalities makes tram-train technology attractive in South Holland.

Israel and tram-trains

In Israel, there are very few historic railways. A large share of construction is new, and therefore has to either swerve around cities or tunnel to enter them, or in a handful of cases run on elevated alignments. Israel Railways and local NIMBYs have generally preferred swerving.

Moreover, the urban layout in Israel is very podlike. There do exist contiguous areas of adjacent cities; Tel Aviv in particular forms a single blob of gray with Ramat Gan, Givatayim, Bni Brak, Petah Tikva, Bat Yam, and Holon, with a total population of 1.5 million. But for the most part, adjacent cities are buffered with undeveloped areas, and the cities jealously fight to stay this way despite extensive developer pressure.

The final important piece in Israel’s situation is that despite considerable population growth, there is very little rail-adjacent transit-oriented development. The railway was an afterthought until the Ayalon Railway opened in 1993, and even then it took until last decade for mainline rail to be a significant regional mode of transport. The state aggressively builds new pod-towns without any attempt to expand existing towns toward the railway.

The upshot is that all three of Jarrett’s criteria for tram-trains are satisfied in Israel, everywhere except in and around Tel Aviv. Tel Aviv is large enough for a fully grade-separated route, i.e. the already-existing Ayalon Railway. Moreover, because Tel Aviv needs full-size trains, anything that is planned to run through to Tel Aviv, even as far as Netanya and Ashdod, has to be rapid transit, using short tunnels and els to reach city centers where needed. A tram-train through Ashdod may look like a prudent investment, but if the result is that it feeds a 45 meter long light rail vehicle through the Ayalon Railway then it’s a waste of precious capacity.

But Outside Tel Aviv, the case for tram-trains is strong. One of my mutuals on Twitter brings up the Beer Sheva region as an example. The mainline going north has a station called Lehavim-Rahat, vaguely tangent to Lehavim, a ways away from Rahat. It could get two tramway branches, one diverging to the built-up area of Lehavim, a small suburb that is one of Israel’s richest municipalities, and the other to Rahat, one of Israel’s poorest. There are also interesting options of divergence going south and east, but they suffer from being so far from the mainline the network would look scarcely different from an ordinary tramway.

Beer Sheva itself would benefit from tramways with train through-service as well. The commercial center of the city is close to the train station, but the university and the hospital aren’t, and are not even that close to the subsidiary Beer Sheva North station. The station is also awkwardly off-center, lying southeast of the city’s geographic center, which means that feeding buses into it with timed transfers screws internal connections. So tramway tracks on Rager Boulevard, cutting off Beer Sheva North for regional trains, would do a lot to improve regional connectivity in Beer Sheva; intercity trains should naturally keep using the existing line.

In the North, there are similar examples. Haifa is not going to need the capacity of full-size trains anytime soon, which makes the case for various branches diverging into smaller cities to provide closer service in tramway mode strong. Unlike in Beer Sheva, the case for doing so in the primary center is weak. Haifa’s topography is the stuff of nightmares, up a steep hill with switchback streets. The mainline already serves the Lower City well, and climbing the hill is not possible.

This creates an interesting situation, in which the technology of the tram-train in the North can be used to serve secondary cities like Kiryat Ata and Tirat Carmel and maybe enter the Old City of Acre, but the operational pattern is really that of a Stadtbahn – fast through Haifa and up most of the Krayot, slow through smaller suburbs.

Job Sprawl as Deurbanization

A few years ago, Aaron Renn was writing, I think about the General Electric headquarters’ move from suburban New York to Downtown Boston in 2016, that in the future, city center jobs would go to high-value industries like corporate HQs and professional services, and then lower-end stuff like call centers would go in suburban office parks. At the time I didn’t understand the full meaning of this – I was still thinking of employment in a narrow city center of a few blocks rather than a broader region, like the 100 km^2 zone I use to compare the US with Canada and France because that’s the most granular data I have in the latter two countries. But in retrospect, Aaron was getting at a dangerous trend in which job markets deurbanize. This is not a new trend – office park sprawl goes back to the 1970s, and industrial sprawl even earlier – and to some extent it’s less about deurbanization and more about the urban job market reaching maximum size. But whatever the history of it, it’s a serious threat to economic performance – and the solution to it requires better public transportation.

Cities as job markets

I’ve written before about production theory. The only thing I have to add on the theory side is that since I wrote that post, I was at a talk that Alain Bertaud gave at Marron, about urbanization. The main topic of the talk was about urban growth and sprawl in the developing world, but at the beginning of the presentation, he gave some remarks about cities and corona. Zoom meetings like the one we had, he warned, were fine, but cities are fundamentally job markets that succeed through spontaneous interaction, and this spontaneity does not exist with remote work. This is to a large extent the new urban geography thesis of Paul Krugman or the work of Ed Glaeser – cities exist as places of production first, and this production requires close proximity.

Now, close proximity depends on technology. In a city with the transport technology of London circa 1800, close proximity means the scope of the City of London, and even 5 km is uncomfortably far. In a city with cars and highways, the distance is much greater – but it is not the same as commute distance. A half-hour drive is not spontaneous. When I asked American friends and coworkers about their productivity through the spring corona lockdowns, a Boston lawyer told me that lawyers wouldn’t even travel midday for clients for 20-30 minutes, since their time was too valuable – they’d schedule conference calls.

This does not mean that the entire work market has to be within such a short distance. It certainly helps, but different industries can cluster in different parts of the city. But there is a maximum distance within which the city is recognizably a single job market.

Aaron Renn’s bifurcation

Aaron talks about bifurcation a lot, between winners and losers. He relates the move of large corporate HQs to city centers to this bifurcation: city centers win by having higher-value added, higher-paying jobs, everyone else gets saddled with lower-end jobs. Moreover, these lower-end jobs are commodities – a call center can be anywhere – and therefore they compete on price and not quality, frustrating the attempt of any region on the margins of the US to climb up the value chain.

That said, even the sort of job sprawl of the 1970s, spearheaded by big companies’ move out of city centers to rich suburbs like GE to Fairfield and IBM to Armonk, represents the same threat to urban productivity. That was driven by snobbishness – the elite suburbanized, and then dragged jobs outside the city with it, for example GE did partly on spurious grounds of resilience in face of nuclear war destroying city centers. Today, the city gains higher-end jobs at the expense of the suburbs, the opposite of the situation in the 1970s. But the same situation of jobs outside one major core persists.

Is this polycentricity?

No. It’s become fashionable to speak of polycentric cities as the next evolution, to decongest old cores. But doing so requires the urban geography to have centers. I pointed out previously that Los Angeles may claim to be polycentric but is just weak-centered – the secondary centers have a few tens of thousands of jobs each at most. This is not like the big city centers one finds in Kyoto, Osaka, and Kobe, or even in the Rhine-Ruhr or Randstad.

Keihanshin, the Rhine-Ruhr, and Randstad are all agglomerations of historic cities. It is possible to also form polycentric regions out of new development – for example, Yokohama was founded as a 19th-century treaty port and then grew as a Tokyo suburb. Both New York and Paris have moved their central business districts by a few kilometers gradually, New York from Lower Manhattan to Midtown and Paris from Les Halles to around the Opera; both also have near-center business centers, like Long Island City or La Défense. Even then there’s likely to be some efficiency loss in decentralizing city center jobs this way, but it’s still easier to shuttle between Times Square and World Trade Center than between either and New Brunswick.

The public transit solution

In the 1970s, the abandonment of city centers was motivated by a desire to escape their poverty and a belief that the suburbs were the future. Urban poverty still exists but inner-urban wealth is considerable and increasing, and the belief that the suburbs were the future turned out to be incorrect – one cannot be a suburb of nowhere.

The model of suburbanization that can be sustained is one built from the late 19th century to about the 1950s and early 60s: jobs stay in the city, people go wherever.

Doing so requires three things: offices, dwellings, and a way of getting between them.

Offices mean commercial upzoning – some American cities are good about it, but the ones with the most demand, like New York, aren’t. In general there’s little appetite for commercializing near-center neighborhoods in the US, whereas Europe is looser about it and therefore new firms can sprout a few subway stops outside the primary center, for example Spotify two stops outside T-Centralen. Residences likewise require upzoning, especially for mid- and high-rise apartment buildings near subway stations where they exist and have capacity.

But in many cases, it’s required to also build up public transportation. Big central business districts feature hundreds of thousands of people converging on a small area at the peak, and the biggest go up into the millions. The highest-capacity form of transportation is required, which is rapid transit, never cars or surface transit.

Rapid transit and city centers are symbiotic, now as in 1910. An expansive rapid transit system, with high service quality, is required to serve city centers from multiple directions; and city centers are required to give people something to take the trains to, or else they’ll just drive everywhere and only take the train to the sports stadium or the airport.

And ultimately, city centers are required for economic efficiency, because of the importance of proximity for spontaneous economic and social interactions. Rapid transit also benefits from high efficiency – it’s very cheap to operate compared with the cost of car ownership. The alternative is a kind of deurbanization, in which people may live at high density relative to travel speeds but don’t form large clusters enabling the highest productivity.

Urbanization in Europe and East Asia

After writing this post about the urban layout of Germany and high-speed rail, I got interested in city size in Europe and Asia more generally. East Asians live in much larger cities than Europeans, and I’m not just talking about Tokyo and Seoul. I was vaguely aware this was the case, but underestimated the size of this effect. By modern definitions of metropolitan areas as those with at least 1 million people, Europe is not majority-urban.


The definitions are hard to harmonize – there are international lists but I don’t fully trust them, many just collating national statistics (like the UN’s) and others making some judgments I am uncertain about, like CityPopulation. I believe the effect I’m discussing is robust to changes in definitions, but its magnitude may be different. I use the following definitions:

  • In Japan, I’m using the major metropolitan area. This is the part I’m least certain about, hence a subsidiary definition based on smaller metropolitan employment areas (MEAs).
  • In South Korea, there are no definitions of a metro area. Seoul is defined as Seoul + Gyeonggi + Incheon, the other cities use city limits.
  • In Taiwan, as in Korea, cities are defined by city limits, except that the capital region consists of Taipei + New Taipei + Taoyuan.
  • In France, a metropolitan area is an aire urbaine.
  • In Germany, a metropolitan area is either the Rhine-Ruhr region, or a Verkehrsverbund.
  • In Italy and Spain, a metropolitan area is cobbled from NUTS-3 regions in 2021 definitions; this can also be used in Germany as a secondary check, but not in France, as French NUTS-3 regions are departments, which aren’t granular enough. Population figures can be found here.



Using the MMA definition, slightly more than half the population lives in the metro areas of Tokyo, Osaka, and Nagoya. Nagoya goes barely over the 50% mark, so the median resident lives either in Nagoya (9.4 million people) or Fukuoka (5.5 million). 56% of the population lives in these four metropolitan areas, 64% lives in metro areas of at least 2 million, 70% lives in metro areas of at least 1 million.

The MEA definition splits polycentric regions like Osaka-Kyoto-Kobe and Fukuoka-Kitakyushu, and also thinks Nagoya is much smaller. On that definition, the median Japanese resident lives in Sapporo (2.4 million), and overall 51% live in metro areas of at least 2 million and 61% in metro area of at least 1 million.

South Korea

The metropolitan area of Seoul has 26.2 million people, which is just a hair over half the population of the country. But it’s so close it’s obligatory to also include the next largest region, which is Busan, population 3.4 million. Together, they have 57% of total population. Daegu adds 2.5 million, and with it 62% of the country’s population lives in cities of at least 2 million. Down to 1 million, the share rises to 70%.


Taipei, New Taipei, and Taoyuan collectively have 8.9 million people, or 38% of total population; Taoyuan is somewhat independent, but Taipei and New Taipei are very closely integrated. The median Taiwanese lives in one of the two second cities, Kaohsiung and Taichung, each with around 2.8 million people; together, 61% live in one of these five municipalities. The next city, Tainan, has 1.8 million people, and including it raises the proportion to 69%.


The Paris region has 20% of the country’s population, and the urbanity of the population craters afterward. Only one more metro area has more than 2 million, Lyon; together, the two regions have 23% of national population. Five more metro areas have between 1 and 2 million people; together, these seven regions have 33% of total population. Even allowing metro areas down to 500,000 only increases the metropolitan share to 44%. The median is either Valenciennes or Le Mans, populations 369,000 and 347,000 respectively.


By any definition, we lump the Rhine-Ruhr into one region of 11,430,361 people, based on the Metropolregion definition (see data here) – usually the German Metropolregionen are way too loose, but in this polycentric region the definition agrees with regional rail extent and with a number of other metro area population lists. In theory this is Germany’s only megacity, but because there are at least 7 independent centers, it doesn’t feel like it’s another London or Paris. Still, it’s 14% of total population.

Using the rather loose Verkehrsverbund limits (still tighter than the Metropolregionen!), we add Frankfurt (6.7 million), Berlin-Brandenburg (6.2 million), Hamburg (3.5 million), Rhine-Neckar (3 million), Munich (2.9 million), Nuremberg (2.8 million), Stuttgart (2.4 million), Bremen (2.2 million), Leipzig-Halle (1.7 million), Karlsruhe (1.4 million), Hanover (1.2 million), Dresden (0.8 million). As a note of caution, some of these regions are drawn very loosely, like Nuremberg, Bremen, and Frankfurt; Hanover and Munich are a lot tighter, Hanover corresponding to a county and Munich to the S-Bahn extent.

On these very loose definitions, the 2+ million regions still only sum up to 49% of the population, and the 1+ million regions to 55%, the median German living in Leipzig-Halle.


Italy has many distinct definitions of metro area, some disagreeing on Milan by factors approaching 2. Eurostat, using provinces as its level of analysis, has metropolitan area for Milan (4.4 million), Rome (4.3 million), Naples (3.1 million), Turin (2.3 million), Brescia (1.3 million), Palermo (1.3 million), Bari (1.3 million), Bergamo (1.1 million), Catania (1.1 million), Bologna (1 million), Florence (1 million), Padua (0.9 million), Verona (0.9 million), Venice (0.9 million), Genoa (0.8 million), Perugia (0.7 million), Messina (0.6 million), Taranto (0.6 million), Reggio Emilia (0.5 million), Parma (0.5 million), Cagliari (0.4 million), Prato (0.3 million).

The four main metro areas comprise 23% of Italy’s population. Going down to 1 million raises the proportion to 37%. These regions combined have only 48% of Italy’s population. This does not mean Italy is majority-rural – the remaining provinces are full of cities in their own right, some larger than Prato or Cagliari – but it’s hard to detect that level of granularity.


In Spain, as in Italy, the division isn’t too granular, at the level of a province. We have metro areas for Madrid (6.7 million), Barcelona (5.6 million), Valencia (2.5 million), Seville (2 million), Alicante (1.8 million), Málaga (1.7 million), Murcia (1.4 million), Cádiz (1.2 million), Biscay (1.1 million), A Coruña (1.1 million), Asturias (1 million), Zaragoza (1 million), Vigo (0.9 million), Tenerife (0.9 million), Granada (0.9 million), Mallorca (0.9 million), Gran Canaria (0.9 million), Córdoba (0.8 million), Gipuzkoa (0.7 million), Navarre (0.6 million), Cantabria (0.6 million), Valladolid (0.5 million), Álava (0.3 million).

The two main metro areas are together 26% of Spain’s population; the next two, down to 2 million people, add up to 35%; the next ones going down to 1 million go up to 55%, the median Spaniard living in a metropolitan province of 1.1 million.

Public Transportation in Megacities

I’ve been talking so much lately about integrated timed transfer in the context of Boston that people started asking me if it’s also applicable to New York. The answer is that the basic principles are not scale-dependent, but the implementation is, so in very large cities, public transport planning should not look like in Switzerland, a country whose largest metro area is staring at 2 million people from the bottom.

The one caveat here is that most cities are not huge. The developed world has seven megacities: Tokyo, Seoul, New York, Los Angeles, Osaka, London, Paris. And Los Angeles doesn’t really have public transportation, so we’re down to six. The middle-income world has a bunch more for sanity checking – Mexico City, São Paulo, Rio de Janeiro, Buenos Aires, Johannesburg, Moscow, Istanbul, Tehran, Beijing, Shanghai, Guangzhou, Shenzhen, Bangkok – but all are either still in convergence mode building up their networks or (mostly in Latin America) have given up. So much of this comes down to the idiosyncrasies of six cities, of which the largest three networks are substantially in the same planning tradition.

Demand is huge

Big cities have big centers, which can’t really be served by any mode except rapid transit. Even in Los Angeles, what passes for a central business district has around a 50% public transport modal split. This means that the transport network has to deliver high throughput to a relatively small city center. Even in a low-kurtosis city like Paris, most Métro lines converge on a narrow area ranging from Les Halles to Saint-Lazare; in a high-kurtosis one like New York or Tokyo, there are a few square kilometers with 200,000 jobs per km^2, which require an exceptionally dense network of rapid transit lines.

Some other network design principles follow from the need to amply serve city center. Specifically, high frequency is rarely a worry, because there’s so much demand even off-peak that usually megacity subway systems do not venture into the frequency range where long waits deter traffic; New York’s 10-minute midday gaps are bad, but that’s unusual and it comes from a combination of the legacy of postwar fear of subway crime suppressing demand and excessive branching.

But other principles require careful planning still.

Electronics before concrete, megacity version

The driverless lines in Paris support peak throughput of 42 trains per hour – a train every 85 seconds. CBTC on Line 13 without driverless operation supports 38 tph, and London’s CBTC-equipped lines support 36 tph when the branching isn’t too complex. It is imperative for other cities to learn from this and do whatever they can to reach similar headways. The difference between 21 tph, as in Shanghai, and Paris’s 42, is equivalent to building a brand new subway line. And what’s more, in a city in the size class we’re talking about, the primary concern is capacity – coverage is already good, so there really is no reason to build two 21 tph lines instead of one 42 tph one.

The situation in Paris is in a context with self-contained lines. That said, extremely busy self-contained lines do exist in other megacities – London has a bunch with near-Parisian levels of throughput, New York has some, Tokyo has a few, Seoul and Osaka are both more self-contained than Tokyo is.

Throughput and organization

The primacy of throughput means that it’s worthwhile to build small infrastructure upgrades, even with concrete, if they help with capacity. Right now the Northern line reverse-branches with the branches to the north recombining with those in the center, and Transport for London would like to split the line in two, reducing branching complexity, which would increase capacity. But doing so requires improving pedestrian circulation in the corridors of the branch point, Camden Town, where TfL expects very large transfer volumes if there’s a split and already there are circulation problems today without a split. Hence the plan in the medium term is to upgrade Camden Town and then split.

If there are bumper tracks at the end of a line, as at 8th Avenue on the L or Flushing-Main Street on the 7, then it’s useful to dig up the street for another block just to add some tail tracks. That way, trains could enter the station at full speed. This increases throughput, because the terminal interlocking has trains heading in opposite directions crossing each other at-grade, which imposes schedule constraints; it’s best if trains can go through the interlocking as fast as possible to reduce the time they’re in a constrained environment, but that in turn requires short tail tracks so that an overrun of a few meters is not catastrophic. Ideally the tail tracks should even extend a full train length past the platform to place the interlocking on the other side of it, as is done in Paris and Moscow; in that case, trains cross the interlocking out of service, when it’s easier to control their exact timings.

Such projects are disruptive, but the disruption is very localized, to just one transfer station for a deinterlining project as in London or one terminal as in New York, and the impact on capacity is very large, if not quite as large as the full suite of signaling and track upgrades that make the difference between a train every 3 minutes and a train every 1.5 minutes.

Network design

The ideal metro network is radial. Megacities already support that just because so many lines have to serve city center. However, it’s important to make sure every pair of lines intersects, with a transfer. No large metro network in the world achieves this ideal – Mexico City’s network is the largest without missed connections, but it is not radial and its only three radial lines are overburdened while the other lines have light ridership. Paris has just a single missed connection on the Métro proper, not counting the RER, but it has many pairs of lines that do not intersect at all, such as M1 and M3. London is more or less a pure radial, but there are a handful of misses, including one without any transfer between the two lines anywhere, namely the Metropolian line (including Hammersmith and City) and the Charing Cross branch of the Northern line.

Big cities that plan out a metro network have to make sure they do better. Missed connections reduce passenger ridership and lead riders to overload the lines that do get connections; for example, in Tokyo one reason cited for the high ridership of the Tozai Line is that until Fukutoshin opened it was the only one with a transfer to every other subway line, and in Shanghai, Line 1 was extremely congested as long as the alternatives going north either had critical missed connections (like Line 8) or avoided city center (like Line 3).

The role of regional rail

Regional rail as a basic concept is mostly scale-invariant. However, the design principles for trains that come every half hour are not the same as those for trains that come every 5 minutes. If trains come every half hour, they had better connect cities in a roundtrip time equal to an integer number of half hours minus turnaround times, so that they don’t have to loiter 25 minutes at a terminal collecting dust and depreciating. If they come every 5 minutes, they’re not going to loiter 25 minutes anyway, and the difference between a 5-minute turnaround and a 7-minute turnaround is not really relevant.

The design principles are then mostly about throughput, again. The most important thing is to build independent trunk lines for trains to serve city center. Even in a huge city, the finances of building a purely greenfield subway deep into suburbia are poor; Tokyo has done it with the Tsukuba Express but it’s mostly above-ground, and for the most part regional lines there and elsewhere come from taking existing suburban lines and linking them with city center tunnels.

Tokyo’s insistence on making these city center tunnels also form a coherent metro network is important. Only one non-Tokyo example is worth mentioning to add to all of this: this is Berlin, which is not a megacity but has three independent S-Bahn trunk lines. Berlin, unlike London and Paris, painstakingly made sure the S-Bahn lines would have transfers with the U-Bahn; its network has only one U-Bahn/S-Bahn missed connection, which is better than the situation in Tokyo, Paris, or (with Thameslink and Crossrail) London.

The role of development

All first-world megacities, and I believe also all megacities elsewhere, have high housing demand by domestic standards. All are very wealthy by domestic standards except Los Angeles, and Los Angeles is still incredibly expensive, it just doesn’t have the high wages to compensate that London and New York and Paris have. In such an environment, there’s no need to try to be clever with steering development to transit-oriented sites. Anywhere development is legal, developers will build, and the public transport system has a role to play in opening more land for more intense development through fast trips to the center.

A laissez-faire approach to zoning is useful in such an environment. This contrasts with smaller cities’ reliance on finger plans, like the original one in Copenhagen or the growing one in and around Berlin. No limits on development anywhere are required. The state’s planning role remains strong through transportation planning, and the suburbs may well form natural finger plans if developers are permitted to replace single-family houses with apartment buildings anywhere, since the highest-value land is near train stations. But state planning of where housing goes is counterproductive – high transit ridership comes from the impossibility of serving a large central business district by cars, and the risk of politicization and policy capture by homeowners is too great.

The advantage of this approach is also that because in a high-demand city public transport can to some extent shape and not just serve development, it’s okay to build lines that are good from the perspective of network coherence, even if the areas they serve are a bit light. This principle does not extend indefinitely – subway and regional rail lines should still go where people are – but for example building key transfer points in near-center neighborhoods that are not in high demand is fine, because demand will follow, as is building lines whose main purpose is to close some gap in the network.

Construction costs

The larger the city, the more important cost control is. This may sound counterintuitive, since larger cities have more demand – only in Manhattan could a $1.7 billion/km extension like Second Avenue Subway pencil out – but larger cities also have a bigger risk of cost blowouts. Already Tokyo has stopped building new rapid transit in the core despite very high crowding levels on the existing network, and London builds next to nothing as well. New York’s poor cost control led Philip Plotch to entitle his book about Second Avenue Subway The Last Subway. Even Paris builds mostly in the suburbs. Extensive city center and near-center construction continues in Seoul, in the context of very low construction costs.

The flip side is that a New York (or even London) that can build subways at the cost of Paris, let alone Seoul, is one that can rapidly solve all of its transport problems. My Assume Nordic Costs map fixates on a region of the world with small cities, but the construction costs in South Korea are if anything lower than in the Nordic countries. And even that map, given free reins for developers, is underbuilt – some lines would look ridiculous at current costs and zoning but reasonable given low costs and liberal zoning, for example something meandering through currently industrial parts of New Jersey.

Small cities designed their public transportation philosophy around scarcity: Switzerland really can’t just draw crayon and build it, because housing and transport demand there are finite and limited. Cities like New York and London, in contrast, should think in terms of abundance of infrastructure and housing, provided their regulations are set up in a way that permits the state to build infrastructure at low costs and private homebuilders to redevelop large swaths as they become easily accessible to city center.

You Do Not Owe Staying to a Failed City

New York real estate media is speculating that people may want to leave the city after the total failures of the city, state, and federal governments to protect public health at the peak of corona in March and April. I do not know if this is actually happening and if people actually are moving out, as opposed to just writing about moving out and complaining that bankrupt retail and restaurant chains are closing. But a number of busybodies, including Mayor Bill de Blasio, have already complained that it is somehow immoral to leave. And the only reasonable reaction to this exhortation is, what?

It’s 100% reasonable to leave a city that cannot provide basic services. The problem with white flight is not that it’s immoral to leave; it’s that it’s stupid to treat segregation as a service the city must provide, rather than education, health care, electricity, transportation, affordable housing, and so on.

A lot of New York’s problems have been well-known for a while. It can’t provide affordable housing to anyone – middle-class renters pay $3,000 a month for an apartment that should be renting for $1,000; everyone in New York knows this, even if many (e.g. homeowners) like this arrangement and some others don’t but have the wrong explanation as for why (e.g. left-NIMBYs). Trash on the street has always been a problem, but only recently have New Yorkers begun realizing it doesn’t have to be this way. Crime was at a historic low on the eve of corona, and even with the recent spike is at sub-2000s levels. Schools in New York are as I understand it good by inner-city American standards.

But the health issue is looming. Six months ago, New York seemed like a place with genuinely good public health. Some of it was cultural (e.g. the city is anti-smoking even by American standards, let alone European or East Asian ones); some of it is selective migration of healthy workers; some of it is high physical activity levels in a city where the majority of people do not own cars, which is a policy issue but one coming from investments made in 1900-1940 and not today. But the hospitals enjoyed good reputation and there is a fair bit of public health care in the city.

And then came corona, and it turned out that the city, the state, and the country all failed at providing basic public health. De Blasio told people to go have fun at bars one last time on the day he announced forced closures in March; Governor Andrew Cuomo outdid him by sending elderly corona patients back to nursing homes, prohibiting subway employees from wearing masks early on, and taking a long time to even acknowledge that masks were useful; and the less said of Donald Trump’s response from when Taiwan first warned the world about the new virus around New Year’s to the present, the better.

The issue isn’t even so much that in the future the city is likelier to have a big second wave. The experience of having heard ambulance sirens all night made New Yorkers take the crisis more seriously than people elsewhere; daily infections are flat and higher than in Europe (36/million people, the EU average is around 23), but so much lower than in the rest of the US. But rather, the total failure of government at all levels to deal with this crisis means it will likely fail to deal with other crises in the future. The US doesn’t have the state capacity to deal with a crisis that democratic East Asia or even Western Europe has, and New York is run as a bunch of fiefdoms at both the city and state level in which the person in charge is selected for political loyalty rather than competence.

The criminal justice angle in New York is even more frustrating. It’s not even that there is crime, or police brutality. Politicians are free to run as pro-police, as Rudy Giuliani and Mike Bloomberg did. But de Blasio ran explicitly on a platform of reducing police brutality, in which capacity he failed – NYPD has killed around 10 people a year every year since the early 2000s. Losing an election is understandable, and even winning the election but then losing in negotiations is understandable and politicians often find themselves having to explain a certain compromise. But de Blasio’s response made no acknowledgment of such compromise – he has no ability to exercise civilian control of the police.

You do not owe anything to a place. Places don’t have feelings, and people who base their entire personal identity on emotional attachment to a place are not worth bothering with. If the city works for you, then great! Move there if you can, stay if you’re already there. There are a lot of great things about New York – New Yorkers are curious and diligent people, even if the people governing them are neither of these things. But if it doesn’t, just leave. It’s okay. I’ll help you with some information about how to move to Germany if you want.

Pedestrianizing Streets in New York

I was asked a few months ago about priorities for street pedestrianization in New York. This issue grew in importance during the peak of the corona lockdown, when New Yorkers believed the incorrect theory of subway contagion and asked for more bike and pedestrian support on the street. But it’s now flared again as Mayor de Blasio announced the cancellation of Summer Streets, a program that cordons off a few streets, such a the roads around Grand Central, for pedestrian and bike traffic. Even though the routes are outdoors, the city is canceling them, citing the virus as the reason even though there is very little outdoor infection.

But more broadly, the question of pedestrianization is not about Summer Streets, which is an annual event that happens once and then for the rest of the year the streets revert to car usage. It’s about something bigger, like the permanent Times Square and Herald Square pedestrianization.

In general, pedestrianization of city centers is a good thing. This can be done light, as when cities take lanes off of roadways to expand bike lanes and sidewalks, or heavy, as when an entire street loses car access and becomes exclusive to pedestrians and bikes. The light approach should ideally be done everywhere, to reduce car traffic and make it viable to bike; cycling in New York is more dangerous than in Paris and Berlin (let alone Amsterdam and Copenhagen) since there are too few separated bike lanes and they are not contiguous and since there is heavy car traffic.

The heavy approach should be used when feasible, but short of banning cars cannot be done everywhere. The main obstacle is that in some places a critical mass of consumers access retail by car, so that pedestrianization means drivers will go elsewhere and the region will suffer; this happened with 1970s-era efforts in smaller American cities like Buffalo, and led to skepticism about the Bloomberg-era Times Square pedestrianization until it was completed and showcased success. Of course, Midtown Manhattan is rich in people who access retail by non-auto modes, but it’s not the only such place.

Another potential problem is delivery access. This is in flux, because drone delivery and automation stand to simplify local deliveries, using sidewalk robots at pedestrian scale. If delivery is automated then large trucks no longer offer much benefit (they’re not any faster than a bicycle in a congested city). But under current technology, some delivery access is needed. In cities with alleys the main street can be pedestrianized with bollards while the alleys can be preserved for vehicular access, but New York has about three alleys, which are used in film production more than anything because they connote urban grit.

Taking all of this together, the best places for pedestrianization are,

  1. City centers and near-center areas. In New York, this is the entirety of Manhattan south of Central Park plus Downtown Brooklyn and Long Island City. There, the car mode share is so low that there is no risk of mass abandonment of destinations that are too hard to reach by car.
  2. Non-residential areas. The reason is that it’s easier to permit truck deliveries at night if there are no neighbors who would object to the noise.
  3. Narrow streets with plenty of commerce. They’re not very useful for drivers anyway, because they get congested easily. If there are deliveries, they can be done in off-hours. Of note, traffic calming on wider streets is still useful for reducing pollution and other ills of mass automobile use, but it’s usually better to use light rather than heavy traffic reduction, that is road diets rather than full pedestrianization.
  4. Streets with easy alternatives for cars, for example if the street spacing is dense. In Manhattan, this means it’s better to pedestrianize streets than avenues.
  5. Streets that are not useful for buses. Pedestrianized city center streets in Europe are almost never transit malls, and the ones I’m familiar with have trams and not buses, e.g. in Nice.

Taking this all together, some useful examples of where to pedestrianize in New York would be,

  1. Most of Lower Manhattan. There are no residents, there is heavy commerce, there is very heavy foot traffic at rush hour, and there are enough alternatives that 24/7 pedestrianization is plausible on many streets and nighttime deliveries are on the rest.
  2. Some of the side streets of Downtown Brooklyn and Long Island City. This is dicier than Manhattan – the mode share in those areas as job centers is far below Manhattan’s. A mid-2000s report I can no longer find claimed 50% for Downtown Brooklyn and 30% for LIC, but I suspect both numbers are up, especially LIC’s; Manhattan’s is 67%, with only 15% car. So there’s some risk, and it’s important to pick streets with easy alternatives. Fulton Mall seems like a success, so presumably expansions can start there and look at good connections.
  3. St. Mark’s. It’s useless for any through-driving; there’s a bus but its ridership is 1,616 per weekday as of 2018, i.e. a rounding error and a prime candidate for elimination in a bus redesign. There’s so much commerce most buildings have two floors of retail, and the sidewalk gets crowded.
  4. Certain Midtown side streets with a lot of commerce (that’s most of them) and no buses or buses with trivial ridership (also most of them). One-way streets that have subway stations, like 50th and 53rd, are especially attractive for pedestrianization. Two-way streets, again, are valuable targets for road diets or even transit malls (though probably not in Midtown – the only east-west Manhattan-south-of-59th-Street bus route that screams “turn me into a transit mall” is 14th Street).

School Transit-Oriented Development

Transit-oriented development, or TOD, means building more stuff in places with good access to public transportation, typically the immediate vicinity of a train station. This way people have more convenient access to transit and are encouraged to take it because they live or work near the train, or ideally both. In practice, American implementations heavily focus on residential TOD, and secondarily on commercial TOD, the latter focusing more on office than retail. I covered some retail issues here; in this post, I’m going to look at a completely different form of TOD, namely public-sector institutions that government at various levels can choose the location of by fiat. These includes schools, government offices, and cultural institutions like museums. Of these, the most important are schools, since a huge share of the population consists of schoolchildren, who need convenient transportation to class.

This principle here is that the state or the city can site public schools where it wants, whether it’s by diktat or by inducements through funding for school construction. This occurs even in situations with a great deal of autonomy: American suburban schools are autocephalous, but still receive state funding for school construction, and if anything that incentivizes moving to new suburban campuses inaccessible by public transit. Other cultural institutes are usually less autonomous and more strapped for cash, and getting them to move to where it’s easier for people to access them without a car should be easier.

School siting: central cities

Urban schools tend to spread all over the city. There are more schools in denser and younger neighborhoods; there also are more high-end schools (Gymnasiums, etc.) in richer neighborhoods. But overall, there isn’t much clustering. For example, here is what I get when Googling both Gymnasiums in Berlin:

There are many Gymnasiums in rich areas like Wilmersdorf and few in poor areas (the map shows one in Neukölln and none in Gesundbrunnen and Wedding, although a few that aren’t shown at this zoom level do exist). But overall, the school locations are not especially rail-oriented. They’re strewn all over the middle-class parts of the city, even though most students do not live close enough to walk. Only the most specialized of the elite schools is in city center, the French school.

The situation in New York is similar to that of Berlin – the schools in the city are all over. This is despite the fact that there’s extensive school choice at the high school level, so that students typically take the subway and bus network over long distances. New York’s school stratification is not the same as Berlin’s – its Specialized High Schools serve the top 3% of city population, Germany’s Gymnasiums serve maybe 30% – but there, too, schools that explicitly aim to draw from all over the city are located all over the city. Only the most elite of New York’s schools, Stuyvesant, is in the central business district, namely in Lower Manhattan; the second and third most elite, Bronx Science and Brooklyn Tech, are just outside Downtown Brooklyn and in the North Bronx, respectively. A huge fraction of Bronx Science’s student population commutes from feeder neighborhoods like Flushing, Sunset Park, Chinatown, Jackson Heights, and the Upper West Side, and has to wake up early in the morning for an hour-long commute.

If schools are not just for very local neighborhood children, then they should not be isotropic, or even middle-class-isotropic as in Berlin. They should be in areas that are easily accessible by the city’s rapid transit network, on the theory that the time of children, too, is valuable, and replacing an hour-long commute with a half-hour one has noticeable benefits to child welfare and educational outcomes.

Urban school nodes

So to improve transit access to school in transit cities, it’s useful to get schools to move to be closer to key nodes on the rail network. City center may be too expensive – the highest and best use of land around Times Square or Pariser Platz is not a school. But there are other useful nodes.

The first class of good locations is central and near-center areas that don’t have huge business demand. In New York, Lower Manhattan and Downtown Brooklyn both qualify – business prefers Midtown. In Berlin, there are a lot of areas in Mitte that don’t have the development intensity of Potsdamer Platz, and to some extent the French school picked such an area, on the margin of Mitte.

The second is key connection points on the rail network that are not in the center. Berlin is rich in such connections thanks to the Ring. To some extent there are a bunch of schools close to Ringbahn stations, but this isn’t perfect, and for example the Europasportspark shown on the map is between two Ringbahn stations, at one of the few arterial roads through the Ring that doesn’t have an S-Bahn station. In New York, there is no ring, so connections are more sporadic; desirable nodes may include Queensborough Plaza, Metropolitan/Lorimer in Williamsburg, and East New York.

East New York supplies an example of the third class: an area that is rich in transit connections but is commercially undesirable because the population is poor. (The Berlin equivalent is Gesundbrunnen – non-German readers would be astounded by the bile Germans I know, even leftists who vote for anti-racist politicians, heap on U8 and on Gesundbrunnen and Neukölln.) Since everyone goes to school, even working-class children, it is valuable to site schools and other cultural amenities in such areas for easy accessibility.

One important caveat is that freeways, which make office and retail more attractive, have the opposite effect on schools. Air pollution makes learning more difficult, and children do not own cars and thus do not benefit from the convenience offered by the car. If rail lines are near freeways, then schools should be set somewhat away, on the principle that the extra 5-minute walk is worth the gain in health from not sitting hours in a polluted environment.

The suburbs

Outside the cities, the place for schools is the same as that for local retail and offices: the town center, with a regional rail station offering frequent access by train and timed connections by bus. Even when the student population is local, as it is in American suburbs, the density is too low for people to walk, forcing some kind of mechanized transportation. For this, the school bus is a poor option – it is capital-intensive, requiring what is in effect a second bus system, one that is as useless for non-students as the regular buses are for students if the school is far away from the local transit network.

Instead, a central school location means that the suburban bus network, oriented around city center, is useful for students. It increases transportation efficiency rather than decreasing it – there is no duplication of service, and the school peaks don’t usually coincide with other travel peaks, like the office worker peak and the retail worker peak. The bus network, designed around a 15- or 30-minute clockface schedule, also means that students can stay in longer, if they have on-campus club activity or if they have things to do in the town center, such as going shopping.

In some distant suburbs the school peak, arriving around 8 in the morning, may be the same as the peak for office workers who take the bus to the train to go to the central city. This isn’t necessarily a bad thing – for parents who insist on driving, this makes it easier to drop off children on the way to work. If this turns out to create real congestion on the bus, then the solution is to move school start time later, to 9 or so.

It’s crucial to use state power to effect this change when possible. For example, Massachusetts funds school construction through state funds but not renovation, which has encouraged schools to move to new campuses, generally in harder-to-reach areas. Fitchburg’s high school used to be in city center but recently moved to a suburban location close to nothing. Even in environments with a lot of local autonomy, the state should fund school construction in more central areas.

Density and Subway Stop Spacing

Normally, the best interstation distance between subway or bus stops does not depend on population density. To resurrect past models, higher overall density means that there are more people near a potential transit stop, but also that there are more people on the train going through it, so overall it doesn’t influence the decision of whether the stop should be included or deleted. Relative density matters, i.e. there should be more stops in areas that along a line have higher density, for example city centers with high commercial density, but absolute density does not. However, there is one exception to the rule that absolute density does not matter, coming from line spacing and transfer placement. This can potentially help explain why Paris has such tight stop spacing on the Métro and why New York has such tight stop spacing on the local subway lines.

Stop spacing and line spacing

The spacing between transit stops interacts with that between transit lines. The reason is that public transportation works as a combined network, which requires every intersection between two lines to have a transfer. This isn’t always achieved in practice, though Paris has just one missed connection on the Métro (not the RER), M5/M14 near Bastille; New York has dozens, possibly as many as all other cities combined, but the lines built before 1930 only have one or two, the 3/L in East New York and maybe the 1/4-5 around South Ferry.

The upshot is that the optimal stop spacing depends on the line spacing. If the line spacing is tight – say this is Midtown Manhattan and there is a subway line underneath Lex/Park, Broadway, 6th, 7th, and 8th – then crossing lines have to have tight stop spacing in order to connect to all of these parallel lines. In the other direction, there were important streetcars on so many important cross-streets that it was desirable to intersect most or ideally all of them with transfers. With so many streetcar lines extending well past Midtown, it is not too surprising that there had to be frequent subway stops.

So why would denser cities have tighter line spacing?

Line spacing and density

The intuitive relationship between line spacing and density is that denser cities need more capacity, which requires them to build more rail lines.

To see this a bit more formally, think of an idealized city on a grid. Let’s say blocks are 100*100 meters, and the planners can figure out the target density in advance when designing the subway network. If the city is very compact, then the subway could even be a grid, at least locally. But now if we expect a low-density city, say 16 houses per block, then the subway grid spacing should be wide, since there isn’t going to be much traffic justifying many lines. As the city densifies, more subway is justifiable: go up to missing middle, which is around 30-40 apartments per block; then to the Old North of Tel Aviv, which would be around 80; then to a mid-rise euroblock, which is maybe 30-40 per floor and 150-200 per block; then finally a high-rise with maybe 500-1,000 apartments.

Each time we go up the density scale, we justify more subway. This isn’t linear – an area that fills 500 apartments per block, which is maybe 100,000 people per km^2, does not get 20 times the investment of an area on the dense side of single-family with 16 houses per block and 5,000 people per km^2. Higher density justifies intensification of service, with bigger and more frequent trains, as well as more crowding. With more subway lines, there are more opportunities for lines to intersect, leading to more frequent stop spacing.

Even if the first subway lines are not planned with big systems in mind, which New York’s wasn’t, the idea of connections to streetcar lines was historically important. A stop every 10 blocks, or 800 meters, was not considered on the local lines in New York early on; however, stops could be every 5 blocks or every 7, depending on the spacing of the major crosstown streets.

Dense blobs and linear density

Line spacing is important to stop spacing not on parallel lines, but crossing lines. If a bunch of lines go north-south close to one another, this by itself says little about the optimal spacing on north-south lines, but enforces tight spacing on east-west lines.

This means that high density encourages tight stop spacing when it is continuous in a two-dimensional area and not just a line. If large tracts of the city are very dense, then this provides justification for building a grid of subway, since the crosstown direction is likely to fill as well; in New York, 125th Street is a good candidate for continuing Second Avenue Subway Phase 2 as a crosstown line for this reason.

In contrast, if dense development follows a linear corridor, then there isn’t much justification for intense crosstown service. If there’s just one radial line, then the issue of line spacing is moot. Even if there are two closely parallel radial lines in the same area, a relatively linear development pattern means there’s no need for crosstown subways, since the two lines are within walking distance of each other. The radial urban and suburban rail networks of Tokyo and Seoul do not have narrow interstations, nor do they have much crosstown suburb-to-suburb service: density is high but follows linear corridors along rapid transit. Dense development in a finger plan does not justify much crosstown service, because there are big low-density gaps, and suburb-to-suburb traffic is usually served efficiently by trips on radial lines with a transfer in city center.

Transportation Renaissance

Ada Palmer posts rarely, but when she does, it’s always worth reading. She alternates between writing about her science fiction and writing about academic history; her most recent post is the latter, covering the historiography of the Renaissance. She notes that the idea of a three-age system, in which great Ancient knowledge was lost in the Middle Ages and rediscovered in the Renaissance, was first promoted in the Renaissance itself, even if the word renaissance was only used starting in the 19th century, and traces why this idea was accepted then and why it’s remained popular since. In short: it provided political legitimacy to the coterie of thugs (“aristocracy”) who launched coups and counter-coups in the Italian states, who could hire historians to portray them as harbingers of a new era of revival of ancient glory.

This is a paragraph-long summary of a 13,000-word post that summarizes an in-progress book, so I’m glossing over a lot of detail and I recommend that people read the post if they want to talk about Renaissance historiography. I bring this up because this is relevant to transportation, and to some extent urbanism in general, in a number of ways.

The three-age schema

Ada notes that medieval Europeans divided the world into two ages: before and after Jesus. The Renaissance began a trend of a three-age system: Antiquity, a medieval dark age, and the Renaissance or modernity. She further traces the intellectual history of this not just in the Italian Renaissance but also in more recent times, going over the use of the language of renaissance in Johan Burkhardt’s work to argue for a new modernity replacing medieval superstition.

Stepping away from professional historians, I do not know to what extent the average educated Westerner thinks in terms of three ages. The answer is clearly “a great deal,” but I do not know to what extent it is universal. I was taught this schema uncritically in primary and middle school, but what I see in the online discourse is less consistent – for example, Paul Krugman’s writings on Malthusianism back a two-age model, before and after the beginning of the Industrial Revolution. But even with the caveat that economic historians don’t view things this way, the Nike swoosh model of Roman greatness, medieval decline, and modern resurgence still exercises enormous cultural influence.

The relevance of this is that people who propose a change to something often default to the three-age model, transplanted into a specific context. The emergent view of most American and European advocates for rail transport is that rail had a golden age from its invention until the middle of the 20th century, declined subsequently, and is supposed to enter a renaissance now. This is usually connected with urbanism, with a model of the growth of traditional cities, decline through suburban sprawl, and renaissance; variants depend on politics, but Strong Towns, myriads of consultants telling cities how to attract talent, most YIMBYs, and most of the left agree on this picture.

Revival of ancient learning

Renaissance Italy had a MIGA obsession. In an era of the Avignon Papacy and intensifying warfare between different factions and city-states, the appeal of Roman unity and peace is not hard to understand; it’s not as if 14th- and 15th-century Italians had better models. Here’s Ada again:

The solution Petrarch proposed to what he saw as the fallen state of “my Italy” was to reconstruct the education of the ancient Romans.  If the next generation of Florentine and, more broadly, Italian leaders grew up reading Cicero and Caesar, the Roman blood within them might become noble again, and they too might be more loyal to the people than to their families, love Truth more than power, and in short love their cities as the Romans loved Rome.  Such men would, he hoped, be brave and loyal in strengthening and defending their homelands.  Rome started as one city, and did not make itself master of the world without citizens willing to die for it.

“Petrarch says we can become as great as the ancients by studying their ways!  Let’s do it!”  Petrarch’s call went out and, with amazing speed, Italy listened.  Desperate, war-torn city states like Florence who hungered for stability poured money into assembling the libraries which might make the next generation more reliable.  Wealthy families who wanted their sons to be princely and charismatic like Caesar had them read what Caesar read.  Italy’s numerous tyrants and newly-risen, not-at-all-legitimate dukes and counts filled their courts and houses and public self-presentation with Roman objects and images, to equate themselves with the authority, stability, competence and legitimacy of the Emperors.  No one took this plan more to heart than Petrarch’s beloved Florentine republic, and, within it, the Medici, who crammed their palaces with classical and neoclassical art, and with the education of Lorenzo succeeded in producing a classically-educated scion who was more princely than princes.

This provided the template for every Western narrative of decline that I’m familiar with, and a good number of non-Western ones: we were great, we’ve gone into decline, we will reverse the decline by restoring our ancient values. It’s unavoidable in every narrative of American decline; it’s there in the Brexit conception of British nationalism; it’s there in cross-national narratives of the decline of the left since the 1970s. In non-Western countries, it was there in a lot of early colonial rebellions (the Indian Rebellion of 1857 tried to restore the Mughal Empire). Even Japan went through a restorationist phase in the wake of its forced opening, though it famously went in a very different direction once the Meiji restoration happened.

This schema is used at a subnational level extensively. Regions that view themselves as declining, like the American Rust Belt, Northern England, or East Germany, cling fiercely to distinctive local institutions. This includes extensive study of local history and local affairs. It’s unavoidable in, say, Belt Publishing. Sometimes, this history is studied critically; in the broad public, it usually isn’t. The number of times I’ve heard New Yorkers contrast how the First Subway was built in four years (and not, say, 40) with how long subways take today is beyond mortals’ ability to count.

With rail transport specifically, advocacy is usually bundled into railfan interests. This, as per the usual paradigm, dovetails into very deep, usually uncritical, study of the history of the technology back when it was supposedly great. Go on and you will see people talk about the minutiae of historical steam and diesel engines and also brush off every piece of knowledge that was not generated in American mainline railroading. Interest in rail technology as a solution for the future gets bundled into romanticism for steam locomotives and for the particulars of how private railroads chose to operate service in the early 20th century.

The Renaissance Man as the innovator

Finally, Ada’s insight about why the idea of the Renaissance was accepted so quickly matters when looking at modern technology. Here, the three-age model is less relevant. The same emphasis on the innovator bringing the company/city/nation/world into a golden age is produced by other models. The accelerating growth model of the technological singularity produces the same effect even without the need to learn history, and is therefore widely popular among rationalists.

In transportation, the best recent example of this is the idea of the Hyperloop. What it is, underlyingly, is a new technology for running rail service, like maglev but capable of running at higher speed. All aspects of rail service planning with the exception of propulsion remain mostly the same (mostly, because the higher speeds do have special implications, though I don’t think they’re any different from what one can extrapolate from existing high-speed rail). This means that what it takes to build Hyperloop is similar to what it takes to build ordinary rail plus more money. I think Hyperloop One and Virgin understand that, but Elon Musk does not.

The importance of history as legitimacy cannot be discounted here. Court historians were hired to write hagiographies, just as artists were hired to paint and sculpt the likenesses of the biggest thugs (“royalty”). This does not usually apply to modern academic history – historians have political biases but there are layers insulating high-prestige academic historians from donors. But it does apply to a lot of popular writing, especially business journalism. I forget where I’ve read – I think it was in the context of New York real estate – that 2010s journalism is alive and well in trade media, but writing critical investigative pieces about powerful players is not always expected or rewarded in publications that make money as internal trade papers.

The upshot is that analyzing history, whether general or specific, as an abrupt positive change serves to empower people who can claim that they are the new world, and that any and all criticism is just the old way of thinking. It’s a form of epistemic narrowing that blocks off knowledge those people don’t have or can’t easily control.