As an addendum to my post about transit cities and centralization, let me explain that the term centralized city really means two different things. One is diffuse centralization throughout the core, typical of pedestrian cities and bus cities and of Paris ex-La Défense; the other is spiky centralization around geographically small transit hubs, for examples Midtown Manhattan, the Chicago Loop, and Central Tokyo. A transit city will tend toward the latter kind of centralization, which is based on walking distance from the subway.

By bus city, I mean a specific kind of urbanism that never existed in the West, but crops up repeatedly elsewhere. It occurs when a city grows too large for walking and cycling while it’s still too poor to build rapid transit, whose construction costs are very high as a share of GDP in developing-world cities. Old buses are not expensive to buy, and their main cost component is labor, which isn’t expensive in a poor city; Beijing for example has only recently gotten rid of conductors on buses.

For a good source on different typologies, I as usual recommend Paul Barter’s thesis – it’s not the main subject of the thesis, but the thesis explains it as background. Bus cities, much like pedestrian cities (which are cities where most people walk to work), tend to be dense all over and monocentric in the sense that there aren’t large suburban centers around them, but they do not have a dominant CBD since buses don’t have the capacity.

Paris is unique among first-world megacities in having preserved this arrangement with its height limits. But it’s still moving in the spiky direction somewhat: the RER has wide stop spacing, which encourages spiky development; and the proposed orbital may be marketed as a circumferential line, but it’s for the most part just a north-south line through La Défense that’s being run together with other lines to potential secondary centers. The difference is that La Défense is more sterile and less pedestrian-friendly than Midtown Manhattan and the Chicago Loop. I may write about this in another post, but greenfield CBDs seem to be always worse for pedestrians than legacy ones, and if the legacy CBD hasn’t evolved to the spiky transit city form, then urbanists may conflate the spiky transit city form with the pedestrian-unfriendliness of the greenfield CBD.

Transit city centralization works differently – it’s based on walking distance from the main rapid transit nodes. Recall that transfers at the downtown end are the most inconvenient for suburban commuters, so that one subway stop away from the center is too far. This makes the transit city CBD inherently geographically small, so that the job density is much higher than that of any other urban form; the job density can also be higher because of the larger amount of space afforded by skyscrapers.

In contrast, the transit city is unlikely to be monocentric. A dominant CBD accessed by rapid transit is a geography that tends to create extremely long commutes – much longer than car-accessible edgeless cities, though not longer than trying to access the same CBD by car – and this leads governments to promote the growth of secondary centers, which are also spiky. Because those secondary centers look like CBDs and not like endless sprawl as do the secondary centers in the US, they make the city look polycentric, even if measured in terms of the CBD’s share of metro area employment they’re very CBD-dominated. When I say a transit city is inherently a centralized city, I do not mean that secondary centers are impossible or undesirable, just that the CBD needs to have a relatively large share of jobs, and that the secondary centers should be actual centers – if they can’t be like Shinjuku, they should be like Jamaica or Newark or how Tysons Corner wants to look in 20 years and not like how Tysons Corner looks now.

For example of how this kind of centralization emerges from the other kind, we can look at the evolution of cities that built large rapid transit networks. Tokyo around Nihonbashi would be the best example, but New York around City Hall is as good. While Lower Manhattan is clearly a smaller CBD than Midtown, it still looks like a spiky CBD, which it did not a hundred years ago. If you plot the locations of the skyscrapers in Lower Manhattan, with few exceptions they’re all south of Chambers, usually far south; peak employment is around Fulton and Wall Streets. The old elevated terminal for Brooklyn trains at Park Row would be inappropriately located. North of Chambers there are city neighborhoods with names like Chinatown or TriBeCa, which are mixed-use enough to have many jobs but have nowhere near the job density of Wall Street.

A related kind of centralization occurs in a multipolar city region, composed of many small cities. None of the cities of the Ruhr is large enough to spawn spiky subcenters on its own, but because the region has grown so interdependent it’s as big as a megacity, the legacy centers in the various cities have turned into a spiky centralization, only without one CBD dominating the rest.

I think it’s the last kind of spiky centralization that transit advocates think of when they propose to turn LA into a multipolar region. Or perhaps it’s in a limbo between a true multipolar region and a unipolar one with well-defined, transit-oriented secondary CBDs. On the one hand, the transit lines proposed in and beyond Measure R are not very downtown-centric. Each direction out of downtown generally gets one line, the exception being the west because of the low-hanging Expo Line fruit and the higher-demand Wilshire corridor. The focus is on connectivity between different poles, since unlike a true transit city Los Angeles has no capacity crunch on its transit system. The subway proposal for going beyond Measure R is to continue south of Wilshire on Vermont, missing downtown entirely, rather than, say, continuing east of Union Station along Whittier.

But on the other hand, the secondary cores are defined in relation to downtown – west (Santa Monica, UCLA), north (Burbank), south (Long Beach), and so on. It’s not like the organic buildup of agglomeration that merged the various cities of the Ruhr into one megaregion, or the merger of the metro areas of New York and Newark, or on a larger scale San Francisco and San Jose. Instead, these secondary cores emerged as secondary to Downtown LA, and only became big because Downtown LA’s transportation capacity is limited by the lack of rapid transit. Put another way, a transit revival in Los Angeles that includes rapid transit construction would make Los Angeles more downtown-oriented rather than less.