Friday, July 21, 2006

The evil of cul-de-sacs?

  Why is auto traffic worse in many new suburbs than in old cities?  One reason is the way that streets and roads are built.  In the old days, cities were built on a grid, which allows for a large variety of options for getting from one spot to another.  As recently as the 1920s, the grid typically was continued out to the new suburbs.  In recent decades, however, private development has moved out far more quickly than governments have built new streets and highways.  Instead of an expansion of the grid, new subdivision developments in the exurbs are typically built as isolated pods, full of cul-de-sacs, attached to the rest of the world only by one or two old roads, once rural but now clogged with ALL the traffic to and from the development.  There's often only one way to get from the self-contained new Swaying Oak Estates community to the rest of the planet.  Residents like this self-contained isolation because it minimizes traffic in the development itself and keeps out people from merely traveling through Swaying Oak Estates.  But when cul-de-sac Flapping Heron Farm development is built on the other side of the single egress and he cul-de-sac Gentle Breezes development is built a mile further out, this single old road (even expanded to six lanes) becomes a parking lot, while taxpayer advocates and smart growth folks nix the idea of building any more "through" roads.   

   A potential solution?  Prohibit developers from building large developments that are full of cul-de-sacs that have only limited access to the rest of the world.  The Twin Cities of Minnesota (also citing supposed communitarian benefits of avoiding cul-de-sacs) have recently made it harder to get approval to build cul-de-sacs.  If new developments were required to be built (with developer money) as extensions of the existing street grid, with many ways to get to and from the new development, new suburbs would be as easy to drive through at rush hour as many older neighborhoods are.

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Cul-de-sacs strike me as an example of "individual rationality, collective irrationality." If I lived in the only cul-de-sac in my neighborhood, life would be good: I could have more privacy and less traffic but would still benefit from the walkability and easy traffic flow of the rest of my neighborhood. But when everyone has a cul-de-sac, walkability deteriorates and traffic congestion explodes.

Posted by: Michael Lewyn | Jul 31, 2006 7:37:10 AM