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Anthony Downs

Jane Jacobs Part II

1946 traffic jam on Mission, near 5th St (Photo: San Francisco History Center, San Francisco Public Library)

When I started this site a few weeks ago, one of the major decisions which had to be made was if this was going to be a local, eyes-on-the-ground nuts and bolts commentary on transportation in Baltimore, or a more theoretical discussion that would touch on the disciplines which make up urban planning. I’ve decided to take both routes and see how it goes.

The last book Jane Jacobs completed before she died was Dark Age Ahead.  It’s meandering, pessimistic, and lacks the Eureka moments of Death and Life.  It’s a rant against the evils (real and imagined) that she felt were crippling society.  One of the more memorable parts of the book is her diatribe against traffic engineers and traffic modeling. Her argument: Traffic isn’t constant. Close a road, and instead of an equal number of cars re-routed, total traffic volumes will be reduced instead. The tried and true theories of fluid dynamics cannot be applied to traffic models since cars are driven by people, and predicting human behavior is more complex than predicting how water flows down a water slide at Wally’s Water World of Fun.

This is similar to Anthony Downs’ Triple Convergence theory; expanding roadway capacity will eventually lead to more drivers using the improved roads, negating whatever capacity improvements have been built. This new traffic comes from:

  1. Drivers who formerly used alternative routes during peak hours switch to the improved expressway (spatial convergence)
  2. Drivers who formerly traveled just before or after the peak hours start traveling during those hours (time convergence)
  3. Some commuters who used to take public transportation during peak hours now switch to driving, since it has become faster (modal convergence). (Stuck in Traffic, 1992)

Two sides of a coin from two very different authors; Closing roads reduces traffic, widening roads increases traffic. The “solution” (road building/widening) creating the symptoms (traffic) which are used to further justify more road building. This never ending cycle has been going on for decades, especially on suburban arterials and commerical strips.

These sacrilegious ideas are being put to use in NYC.  The Madison Square Pedestrian Project, the Broadway Blvd Midtown Improvements, and the 34th St. Midtown Pedestrian Mall show that eliminating full traffic lanes on busy streets in order to create outdoor living rooms, cafe space and transit/bike lanes is not only technically possible, but has enormous quality of life benefits.  Baltimore has also removed a full lane of traffic on Pratt St. (one of the busiest streets in the city) with little impact on congestion and replaced it with a dedicated bike/bus lane for the Charm City Circulator.

While traffic modeling is a useful tool, we should keep an eye on the big picture.