The City:
Jane Jacobs
Effects of Large Buildings
Jane Jacobs --- an unconventional observer of economies, especially city economies --- famously argued that successful neighborhoods provide "eyes on the street" to protect us from crime... It is yet another example of a positive externality: When I go to the park, I not only make it more interesting for other people, I also make it feel safer. That may attract more of them and they will make me feel safer. Empty streets are dull and feel dangerous, so they stay empty. Bustling streets are interesting and safe. Is it any wonder that they are bustling?
Jacobs emphasized the importance of the fine details of streets and building design. She would not, I think, have been much surprised by the quiet spots in Victoria Park, given how hemmed in it is by other parks, the canal, and a busy roadway. Nor would she have found the oscillations around Hackney Downs playground unexpected. The playground and park are the only green space for a mile or more around in a relentlessly urban setting. If they felt safe and interesting they would be well used, but they get little support from their environs, bordered on one side by a railway line, another side by a high-fenced school, and a third side by faceless high-rise public housing. These neighboring uses do not encourage people to stroll across the park, except at the beginning and end of the school day. So the playground has to be completely self-sustaining --- which on good days it can be.
Architecture, too, mattered a lot to Jacobs. There was more than aesthetics at play when a high-rise was built. These tall apartment buildings tended to lift eyes away from street-level and make the streets more dangerous: You cannot leap up from your vantage point on the stoop and dash across the street to rescue the victim of a stabbing if you live on the fourteenth floor.
Jacobs was a brilliant student of urban life, and her theories have hypnotized many readers. But while plausible, those theories have not always been easy to put to the test. Two economists, Ed Glaeser and Bruce Sacerdote, have now managed to put together data to test whether these big apartment buildings really do cause crime.
Some of the subtleties of architecture are simply impenetrable to a number-crunching approach, but Glaeser and Sacerdote studied nearly fourteen thousand city dwellers and were able to examine Jacobs's thesis with surprising precision. Comparing high-rise public housing with high-rise private housing, low-rise public with low-rise private, and using statistical tools to adjust for other factors such as race and poverty, they found that Jacobs seems to be right. They discovered that residents of big apartment blocks were more likely to be victims of crime and were more likely to fear becoming victims. And it wasn't because large blocks are often for public housing: The size of the building itself was the problem.
You might think the reason for this is not rational but psychological: Perhaps big apartment blocks squeeze people into small spaces and make them angry and more likely to commit crime. Or perhaps the problem is purely physical, as it would be if high-rise apartments were more vulnerable to burglary.
Glaeser and Sacerdote don't think so. They found that buildings do not create an environment that encourages crime in general. They don't, for example, facilitate petty larceny (say, lifting a purse from your bag) or even burglary. Big buildings encourage only street crime, such as car thefts or robberies with violence. That suggests that the big buildings are exerting a sphere of malign influence over the streets around them --- or, perhaps more accurately, they are failing to exert an aura of safety, which smaller homes naturally do.
The architectural effects on crime were all about eyes on the street. Glaeser and Sacerdote found, for example, that it was tall buildings (rather than simply large ones) that really failed to keep the streets around them safe. Each additional floor in your building increases your risk of being robbed in the street or having your car stolen by two and a half percentage points --- if your building has twelve stories rather than two, your chance of being mugged rises by a quarter. The higher the building, the more people are lifted away from the stoop and the street. Since Glaeser and Sacerdote adjusted for poverty, public housing, and many other factors, that is a big effect coming from mere steel and concrete. Jane Jacobs was right: The architecture of city neighborhoods isn't just about what looks nice. It's about whether the neighborhoods themselves live or die. And the pernicious effect of the tower blocks falls unevenly. In the United Kingdom, for example, whose population is 92 percent white, racial segregation is vertical: Whites are in the minority of those who live above the fifth floor of a tower block. The British ghettos are up in the sky.
The eyes-on-the-street model, like the chessboard model of segregation, tends to push toward extremes. Either the neighborhood is interesting and lively and safe, in which case it will bustle with activity and stay interesting, lively, and safe, or it is dull and dangerous, in which case it will be shunned and will stay dull and dangerous. But the encouraging thing about eyes on the street is that, unlike Schelling's chessboard model of segregation, there is nothing fundamental pulling cities toward the bad equilibrium. The good equilibrium, where diversity and liveliness are self-sustaining, is always there under the surface, waiting to get out if given half a chance by urban planners.
The Rational Economics of
an Irrational World
Tim Harford
©2008 Random House