Over the years there have been no shortage of ideas about how to design crime out of a city. Jane Jacobs believed a certain degree of street activity — "eyes on the street" — could deter criminal behavior through shared surveillance. James Wilson and George Kelling famously suggested that small signs of physical disorder, things like broken windows, could encourage larger crimes. More recently, there's been evidence that even something as simple as street vegetation can have an impact on the safety of a neighborhood.
These ideas, and many others like them, suggest ways that the built environment of a city can influence criminal behavior. But even before developers build a bar, or a public park, or a bright sign in a neighborhood, the area must be zoned for certain uses: residential, commercial, mixed, and the like. While the theories on designing away urban crime usually focus on what's built in a place, very few studies have considered the role of zoning itself. Turns out it may be a critical one.
A group of researchers led by behavioral scientist James Anderson at RAND recently address this question directly in a pair of studies focusing on Los Angeles. What they found was that zoning indeed predicted the criminal activity of a neighborhood, with residential areas safest, followed by mixed-use residential and commercial zones, followed by commercial-only places. Their findings, published in the University of Pennsylvania Law Review [PDF], lend support to the idea that city officials can improve the safety of a neighborhood by doing something as simple as zoning part of it for residential living:
Our central finding is that blocks that include both residential and commercial zoning exhibit less crime than blocks that are zoned exclusively for commercial use. This result suggests that including some parcels with residential-only zoning on blocks that are otherwise zoned commercially might reduce crime. We also find that crime rates are lowest in residential-only blocks, even in relatively high-crime neighborhoods.
Anderson and his fellow researchers reached their conclusions over the course of two studies. In their first, they found 205 blocks in 8 areas of Los Angeles (e.g. Hollywood, Southeast L.A., Highland Park) with medium-to-high levels of crime and similar demographics. They analyzed the relationship between zoning type — residential, commercial, mixed-use, or manufacturing — and total crime in the area. They focused on crimes that were likely to occur in public view, such as burglaries or car theft, since those are the activities theoretically deterred by urban form.
The researchers found that, all else considered, residential blocks had less crime than blocks with mixed-uses or strictly commercial activity. The implication, of course, is that something about residential areas deters criminals, and something about commercial businesses attracts them.
By itself this study had some limitations — namely, that the zoning of these neighborhoods occurred a long time ago, so other factors could have since influenced the nature of the area. So to enhance their results the researchers identified other areas of Los Angeles where zoning codes had been changed between 2006 and 2010. They paired these areas with other parts of the city that had similar criminal trajectories before this period (from 1994 to 2005) but had not been given new zoning codes. In simple terms, they compared zoning changes with zoning stability.
Once again, the researchers found that residential zoning seemed to play a powerful role in crime deterrence. Most of the zoning changes that occurred (30 percent) shifted strictly commercial areas into mixed-use residential and commercial areas. With the addition of residences, crime dropped about 7 percent, according to Anderson and colleagues. Car thefts (along with thefts from cars) experienced the biggest decline.
So, Anderson and colleagues conclude, "residential parcels seem to reduce crime in commercial areas." Exactly why that's the case remains an open question, though the researchers did weigh in on some of the more popular theories proposed over the years. Jacobs's "eyes on the street" got little support from the data (for instance, bars attracted eyes but also crime), while Wilson and Kelling's "broken windows" got quite a bit of support (things like litter, glass, and garbage were associated with crime too). The researchers leave that for others to address in time; for now, the idea that zoning might not just influence the nature of a neighborhood but also its safety, is enough food for thought.