The Rules of Contagion

motorcyclists to wear helmets. Over the next six years, motorcycle
thefts fell by two thirds. The reason was simple: inconvenience.
Thieves could no longer decide to steal a motorcycle on the spur of
the moment. Instead, they’d have to plan ahead and carry a helmet
around. A few years earlier, the Netherlands and Great Britain had
introduced similar helmet laws. Both had also seen a massive drop in
thefts, showing how social norms can influence crime rates.[88]
One of the best-known ideas about how our surroundings shape
crime is the ‘broken windows’ theory. Proposed by James Wilson and
George Kelling in 1982, the idea was that small amounts of disorder –
like broken windows – could spread and grow into more severe
crimes. The solution, therefore, was to restore and maintain public
order. The broken windows theory would become popular among
police forces, most notably in New York City during the 1990s, where
it inspired a heavy crackdown on minor crimes like subway fare
dodging. These measures coincided with the massive drop in crime in
the city, leading to claims that arrests for misdemeanours had
stopped the larger offences.[89]
Not everyone was comfortable with the way that the broken
windows theory was adopted. One of them was Kelling himself. He
has pointed out that the original notion of broken windows was about
social order rather than arrests. But the definition of public disorder
can be a matter of perspective. Are those people loitering or waiting
for a friend? Is that wall covered in graffiti or street art? Kelling
suggested that it’s not as simple as just telling police officers to
restore order in an area. ‘Any officer who really wants to do order
maintenance has to be able to answer satisfactorily the question,
“Why do you decide to arrest one person who’s urinating in public
and not arrest another?”’ he said in 2016. ‘If you can’t answer that
question, if you just say “Well, it’s common sense,” you get very, very
worried.’[90]
What’s more, it’s not clear that aggressively punishing minor
offences was the main reason for New York’s decline in crime in the
90s. There’s little evidence that New York’s reduction was a direct
result of broken windows policing. Many other US cities saw a drop in
crime during that period, despite using different policing strategies. Of