From WSJ

U.S. violent-crime rates fell for the fourth consecutive year in 2010, as police agencies across the country reported significant decreases in murders, robberies and property crimes, the federal government said Monday.

Among violent crimes, robberies registered the biggest decline, down 10% in 2010 compared with 2009, while rapes decreased 5%. Murders fell 4.2% during the same period.

Property crimes fell for the eighth consecutive year, with motor-vehicle thefts decreasing 7.4% in 2010 from a year earlier and burglaries down 2% during the period.

Like driverless cars I think the significance of this is underrated. Cities display increasing returns to scale. That is, the more people you pack into one area the more productive they are.

The obvious question then is – why isn’t the world just one big city?

There are a couple of issues

  • Provision of clean water
  • Removal of waste materials
  • Contagion
  • Congestion
  • Import of raw materials and food
  • Weakening of Social Monitoring

The first two were solved with modern plumbing and were the secret to the first big booms in cities. The third was solved with antibiotics and vaccination and allowed cities to have a net native population growth.

It used to be that cities were so dangerous that they were a net population sink. You went to the city to get rich, catch consumption and die early.

The last three are still a problem. Subways help with congestion and driverless cars probably still will more. Nonetheless, the extent of the city is limiting in part by congestion.

Transportation costs are falling but the United States still has multiple cities in large part because different areas of the country are close to different important resource areas.

The last one – the weakness of social monitoring – is why cities are great for artists but young couples raising a family are more hesitant. The anonymity of the city means you can get away with more. That might mean an alternative life style. It might mean rape and murder.

However, with violent crime falling another barrier to urbanization is falling and an opportunity to reap the gains of agglomeration will present itself. I haven’t read Ryan’s book yet but my feeling has been that the future belongs to the New Urban Sunbelt.

The crime to density ratio has always been high here and as it falls that’s good news for sunny cities in the South.