Polycentricity

VRE Train.  Image from Ouij on Flickr.

VRE Train. Image from Ouij on Flickr.

Nobody would argue with the idea that DC’s commuter rail system could be better.  Metro, however, is largely praised (disaster responses and publicity notwithstanding).  However, Metro also gets attacked in some quarters for its hybrid nature as both an urban subway and a commuter rail system.

Richard Layman in particular likes to emphasize the writings of Steve Belmont.  When talking of transportation, Belmont contrasts monocentric transit systems (essentially dense hub and spoke networks with all lines serving a dense core) with polycentric ones, where the city has many nodes and thus requires many links between them.  Belmont (and Layman) argue that polycentric is bad and monocentric is good – at least at encouraging dense development and urban living within the core.  The problem, however, is that the monocentric/polycentric division isn’t all that useful when only comparing one system to another.

Belmont’s two main criteria for determining the centricity of rail transit systems are station density and the spatial extent of the system.  Metro in DC fails on both accounts, as it has long ‘tail’ lines and stations separated by long distances.  However, within the core, the station density is actually quite high – extremely high when you consider the context and time it was built (as opposed to the older systems in New York et al with predominantly cut and cover construction).

Paris, on the other hand, is the textbook case of monocentric rail transit, Belmont argues.  Paris’s Metro has more line miles than DC’s Metro, but all of them are squeezed into an area no more than 7-8 miles in diameter.  Likewise, there are far more stations within that smaller area.  It’s an incredibly dense system.

Where the comparison breaks down, however, is the limitation in comparing one system to another.  DC’s Metro is a hybrid system and needs to be analyzed as such.  To make it as close to an apples-to-apples comparison, you’d need to analyze a combined system of both Paris’s Metro and RER.

Jarrett Walker did just that.  The end result is that Paris’s employment patterns are far more polycentric (and as Walker argues, more akin to Los Angeles rather than New York) than Belmont might imply. Walker’s starting point was Alon Levy’s proposal for through-running commuter rail trains in New York (Part 1, Part 2), a theme I picked up on with ideas for DC’s commuter rail system.  Walker writes:

But when you start looking at the cost/benefit of all the tunnelling to get the various commuter lines connected to each other, you stumble on an important difference between Paris and New York.  For all the suburbanization of the last 70-some years, New York still has an world-class concentration of jobs and activities in a very compact core (roughly the southern half of Manhattan plus inner Brooklyn).  For trips from the outer suburbs to this core, it’s not hard to get where you’re going with the existing commuter rail line and one connection to the subway.

Paris commutes are widely distributed to major employment centers located mostly on the edges of the city.  This pattern particularly cries out for RER-style through-running of commuter rail because so many people are commuting to a center on the far side of the city from their origin — for example, from suburbs east of Paris to La Défense in the west.  Greater New York would benefit from such an arrangement, but not nearly as much as Paris does.  For New York it’s a nice feature, but for Paris it’s foundational to the growth pattern of the city.

Polycentricity is the fundamental pattern for the region.  This statement could apply just as easily to DC (especially in terms of employment clusters) as it does for Paris, which is why the through-running concept is so attractive.  The Overhead Wire has some great images talking about how we shape that polycentric reality that most cities deal with.

Walker’s takeaway message is this:

Los Angeles and Paris have come to their similar structures by very different paths, and have drastically different cultures of planning.  But urban structure is destiny because it changes so slowly and incrementally.  The constellation of major centers in both cities is a tremendous advantage for transit: people are flowing in all directions to centers on various edges of the city, so there is a huge area in which transit demand is two-way.  By contrast, suburban commuter service into New York will always be a story of trains and buses flowing empty or nearly empty in one direction so that they can run full in the other, because the concentration of jobs in the center is so massive.

I can’t think of a better vision for DC’s future – a dense core employment area, surrounded with high density neighborhoods – and other employment centers around that (Rockville, Bethesda, Silver Spring, Alexandria, etc).  Enabling, where possible, DC’s commuter rail system to offer through-service to those centers would be a huge improvement in service for DC’s current (and future) economic geography.

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4 Responses to “Polycentricity”

  1. Richard Layman Says:

    Please fairly reflect my utilization of Belmont’s general point that the WMATA system is polycentric, but with my extension of his idea that at the core of DC, the WMATA system, albeit unintentionally, functions monocentrically.

    You say this, but I made the point in 2007, and I continue to make and extend this point in my writings.

    The first mention is buried in this entry, which was the outline for a paper on creating a linked land use and transportation planning paradigm for DC: http://urbanplacesandspaces.blogspot.com/2007/05/congestion-pricing-and-tolls-arent.html

    Nice blog. Didn’t know about it.

  2. Alex Block Says:

    Thanks for commenting, Richard.

    I know your position is more complex than I paraphrased, but such is the problem with being concise. I wasn’t trying to usurp that idea, just comment on it.

  3. tsarchitect Says:

    Great analysis. I suspect that Gaithersburg, Silver Spring, Annandale, Landover, and Tysons will become major secondary centers of business. The real issue will be permitting the growth and nurturing it with transportation.

  4. Transit Planning and the Big Picture « city block Says:

    […] commented previously on the (potential) similarities between DC and Paris – (Polycentricity and Commuter Rail).  The opportunities for through-running service on  various commuter rail […]

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