Affordable Housing Institute : US

[Continued from yesterday’s Part 1]

 

Reading Bruegmann, I was reminded of Nancy’s and my visit to Hoh Rain Forest, about which I wrote:

 

Hoh Rain Forest

 

Big leaf maple trees form the far overhead canopy, their limbs draped with blankets of epiphytes – small ferns that live on the branches, which they use solely for anchor, living purely by drawing nutrients from the moist air.  Almost every maple branch is gauzily sheathed, as if the trees were large lumbering ogres dressed by a fey god.  Mosses cover rocks like deep-pile carpet, ferns rise two feet from the floor. 

 

In Hoh, and later in the Atherton Tablelands,

 

Atherton Tablelands

 

and still later, in the highlands of Papua New Guinea) I found myself reflecting on the complexity of ecosystems:

 

This temperate rain forest is always dying and always growing.  Saprophytic plants grow on dead plants, such as the sconce mushrooms that infest low tree trunks.  Tall trees, some of them two hundred feet in length, crash to the forest floor, where their three-foot trunks form a wall.  Then seedlings fall, a lucky few on the nurse log (as it is known) where their height advantage (a couple of feet above the forest mulch) makes them much more likely to survive.  Eventually, as they grow, the nurse log rots underneath them, so they extend roots down.  Finally the nurse log itself is gone, its only mark a line of trees like marching columns.

 

Nurse log growth, Hoh Rain Forest, Olympic peninsula, Washington

 

We see the nurse log phenomenon in the persistence of streets (a city’s circulatory system) even as every building that abuts them decays, is torn down, and rebounds anew into something taller, shinier, more modern:

 

The conversion of rental buildings, loft structures, and office towers into condominiums not only allowed for a rapid expansion of home ownership at the core of American cities, but the process made possible a large infusion of new money into old buildings.  Behind the carefully preserved facades, many central cities have been thoroughly transformed as part of the same decentralization process that has been at work throughout metropolitan regions.  They participated just as fully in sprawl as the farthest subdivisions.  (Sprawl, page 54)

 

Ironically, this spontaneous community of new urbanism, far from being sprawl, creates its own sophisticated living density:

 

Scattered development often results, in the end, in densities higher than those that would have been achieved with continuous development because it allows for infill at higher densities in the second and third waves of growth.  (Page 67)

 

In this enforcement, foreclosure, and demolition all play a role; tax liens are anaerobic bacteria, all part of the cycle … even as some cities are dying of natural causes, or hit with such shocks (possibly Old New Orleans?) as to be mortally wounded.

 

What then makes a city work?  Are there minimum and maximum densities, and are these invariant with time?

 

Certainly there’s a maximum.  At about 100,000 people per square mile, we hit what appears to be the practical ceiling of viability, although people have lived more closely still:

 

New York City saw its apogee of density only in the early years of the twentieth century when parts of the Lower East Side of Manhattan peaked at more than 400,000 people per square mile, or more than 600 people per acre. 

 

Lower East Side, 1873

 

Contrary to what you might have thought, maximum urban density has not increased with technology, indeed some of the world’s densest areas have been the most humble:

 

These were probably the highest densities recorded to that date and rival some of the densest districts in cities today, notably certain neighborhoods with vast numbers of new immigrants in Hong Kong, Manila, Cairo, or Mumbai (Bombay).  (Page 27)

 

Slums in Mumbai (Bombay)

 

Nairobi’s Kibera, Africa’s largest slum, has densities comparable to that historical Lower East Side, even with one-storey dwellings and a total absence of urban services:

 

Overlooking a slice of Kibera, June, 2005

 

There is also an economic lower bound:

 

1,000 people per square mile is today about the lower limit at which full city services like water supply and waste-water treatment can be provided in a way that most public and private agencies consider economical.  (Page 61)

 

Below that level, you will have a human community, but it will be unincorporated and little resemble what we all imagine as a city. 

 

If we use mass transit as a city indicator, then the required density is one order of magnitude greater, about 10,000 people per square mile (somewhere in Bruegmann; I have lost the citation).  Using some reasonable assumptions (60% of land area for residential, 2.75 people per household), we thus have the following rough scaling grid:

 

People per		Households	Acres per	Square feet	“Personal
sq mile	What it implies	per acre	household	per person	square”
1,000	Lower limit of municipal services	0.3	2.9	46,500	216
10,000	Mass transit effective, popular	3.4	0.3	4,600	68
100,000	Upper limit sustainable density	34.1	0.03	500	22
400,000	Highest levels recorded	136.4	0.01	100	10

 

The “personal square” is my own invention.  Imagine everyone standing in an square grid like an enormous chessboard; the “personal square” is the length of each person’s individual space.  In Kibera 2005, and the Lower East Side 1900, it was ten feet. 

 

On a lighter note, to me mass transit distinguishes city from suburb.  For instance, from where I live in Cambridge to my Boston office, the subway is superior. 

 

My house to work, by car, note the curlicue path (subway much faster!)

 

From there to the airport, it’s comparable (depending on day and time). 

 

My house to the airport, a cab is often faster

 

To my mother’s house in Marblehead, it’s possible (three subway seats and a bus ride, plus two walks) but highly inconvenient.

 

Public transport would take you an hour and a half

 

Yet though mass transit may usefully delineate city from suburb, and though we may adore London’s Tube or the Metros of Paris of Washington DC, a quality subway is no guarantee of city livability:

 

The Tokyo area, despite the city’s very high densities and one of the best public transportation systems in the world, has some of the world’s longest commuting times.  (Page 141)

 

That’s significant, as among the greatest passions of anti-sprawl reformers is their mantra extolling mass transit, be it light rail in Seattle or the Los Angeles subway.  But Bruegmann suggests that such romanticism is merely self-interest prettied up for export:

 

The link with self-interest is often not as clear, as for example in the case of individuals advocating increased mass transit who are very unlikely to use much if it is built.  They assume that someone else will ride it and free up highway space for themselves.  (Pages 161-2)

 

Dallas’s light rail, touted as an anti-sprawl initiative

 

Who then most vehemently opposes sprawl?  Not whom you might think, the low-density gentry:

 

Anti-sprawl agitation is much more intense in the Los Angeles region, with over 7,000 people per square mile, than it is in Little Rock or Lubbock, with densities under 2,000 people per square mile.  If the anti-sprawl crusade were really about using less land or using it more efficiently, the biggest metropolitan areas are illogical targets.  (Page 69)

 

As Bruegmann demonstrates, even as houses have grown larger, average lots have grown smaller (great graph on page 68).  And, though sprawl seems to be decelerating in America, it has migrated overseas:

 

As cities across Europe have become more affluent in the last decades of the twentieth century, they have witnessed a continuing decline in population densities in the historic core, a quickening of the pace of suburban and exurban development, a sharp rise in automobile ownership and use, and the proliferation of subdivisions of single-family houses and suburban shopping centers.  All of these changes have been very beneficial for many urban inhabitants.  But, predictably enough, for many highbrow observes, they are just more sprawl, and they need to be fought with every tool in the planner’s arsenal.  (Page 199)

 

Professor Bruegmann’s history of sprawl and his fascination with cities intersect late in the book in his extended examination of Portland, Oregon, and its three-decade experiment with judicial urban planning.

 

That subject is itself worth of yet another (future!) blog post.

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