In recent years, urban planners have come to accept a somewhat counter-intuitive theory called "induced demand." The theory posits that when you build a new road or widen an existing one to try to ease traffic congestion, the roadway almost always fills to its maximum capacity and traffic congestion grows even worse than it was before. In the mid-1990's British researchers discovered that the opposite of "induced demand" is also true. When roads are narrowed or altogether eliminated, or when it is less convenient or more expensive to drive, traffic doesn't just pile up elsewhere. Rather, traffic disappears.

Traffic jams, it turns out, are the result of tens of thousands of individual human decisions. When it is no longer convenient to drive, especially in a big city with lots of other travel options, a number of commuters will decide to take a different mode of transportation, travel at a different time of day, car-pool, make fewer, more efficient trips, or simply stay at home. The corollary to "induced demand" is often called the theory of "disappearing traffic."  

Thanks to the work of UCLA urban planning professor Donald Shoup, city planners now have a significant body of evidence to show that the theories of induced demand and disappearing traffic also apply to parking. In his book, The High Cost of Free Parking, Shoup showed that the more cheap, abundant parking that cities build, the more traffic congestion and automobile dependence cities get.

Shoup's findings, however, do not yet appear to be influencing New York City's official approach to land use and transportation planning, particularly in the booming outer boroughs. While city regulations hamper the construction of new parking in Manhattan below 96th Street and Long Island City, the Department of City Planning still attaches off-street parking requirements to new construction projects in much of the rest of the city, even in areas as transit-rich as Downtown Brooklyn and Flushing, Queens. Remarkably, the Hudson Yards rezoning on the west side of Manhattan also included minimum parking requirements despite the fact that billions are being spent to extend the number 7 subway line to reach it.

In other parts of the city, including all of Staten Island, officials have established "low density growth management areas," that maintain a more suburban character (including all of Staten Island). Part of the mayor's plan to quell over-development includes strict limits on how dense development can be and higher levels of required parking attached to residential buildings. According to the city's zoning handbook, the city's goal is to "accommodate high auto ownership in these outlying areas distant from mass transit."

Matthew Roth of Transportation Alternatives finds all this exasperating. City officials "fail to acknowledge what their colleagues in the field have long recognized as indisputable truth: the demand for driving is elastic, dependent upon the amount of driving and parking space that is made available."

If City Hall is hedging its bets, the anti-parking argument is often a hard sell at community board meetings and local negotiations where new development projects are being discussed. It is virtually a rule: When a large new development is proposed, locals push for the construction of more parking.

Martha Bitterman, the district manager of Queens Community Board Seven, which includes downtown Flushing, said that she had heard the argument that more parking will lead to more traffic. But she believes that an outer-borough "mentality" means that people will drive at all costs. "You can't say there's not ample public transportation to get in and out of Flushing. But no matter what rules or regulations, or if you jack up the prices, people will still drive," she said.

The recurring debate is particularly strange because both sides appear to have the same goal -- less traffic congestion. Yet, one side argues that building more parking space will achieve that goal. The other side says building less parking space -- or, at least, charging more money for it -- is the way to convince people to get out of their cars.

Unfortunately, debates about big new development projects are not marked by their capacity to digest such nuanced thinking, says Gale Brewer. She has spent decades attending such meetings as a community board member and now as a member of the City Council (Brewer recently introduced a congestion relief bill, which does not directly address parking).

Brewer says that parking comes up at virtually every community meeting she attends, inevitably inspiring such vitriol that she regularly excuses herself "to go to the bathroom" when the issue arises.

"People almost get into fistfights over this," she says.

Photo: photogirl58/Flickr

"As this city is booming, it's not moving," lamented City Councilmember Gale Brewer outside City Hall yesterday. But with support from 125 civic groups in five boroughs, the Citywide Coalition for Traffic Relief assembled behind her and outlined an agenda that could change that condition. The coalition, which formed around a year ago, calls for a 15% reduction of traffic by 2009. The plan calls for a serious study of congestion pricing, strict enforcement of parking regulations, and more room on the sidewalks for bicyclists and pedestrians.

Upper West Side City Councilmember Gale Brewer announced that the council will hold hearings next year on Intro 199, legislation that she has introduced to compel DOT to put in place a more meaningful set of performance measures and specific targets for traffic reductions. She also said she would schedule hearings on a DOT study due in 2007 that will count vehicles, violations and pedestrians on Manhattan's west side, from Central Park to the Hudson River and between 57^th Street and 86^th Street.

Gorman Reilly of Civitas Citizens called for "more improved bus service." Sandra Garcia, a member of the community-based organization Sustainable South Bronx urged reducing truck traffic and reconceiving the little-used Sheridan Expressway as a waterfront greenway. Transportation Alternatives executive director Paul Steely White told the crowd that 22 percent of all car trips in the city last less than a mile and that one in ten drivers in Manhattan's core are cruising for parking space.

The coalition plans to work with elected officials and within its network to promote sensible reform. As Transportation Alternatives' Matthew Roth told the crowd, "New York is a city of pedestrians." With 125 members, the coalition is pressing the city's officials to bring the law into step with the facts.