Researchers at the University of Connecticut undertake a painstaking survey of parking infrastructure in cities

There is no single, handy database that tracks the proliferation of parking spots in a city over time. A five-story parking garage goes in here, a surface lot there. A new development comes in, and zoning code mandates additional spots per housing unit or office desk (or per junkyard, pet cemetery or rifle range) [PDF].

"It’s easy to say on a project-by-project basis, 'Oh, here a parking lot went in because of that project,'" says Chris McCahill, a doctoral candidate in civil and environmental engineering at the University of Connecticut. "Our idea was to look at the huge city-wide scale. What happens to a city when, project by project, that happens?"

To determine this, McCahill and Norman Garrick looked for the best comprehensive surveys they could find: aerial photographs of cities. Then they then set about trying to figure out where all of the parking lots are. They’ve done this in New England with New Haven, Hartford, and Cambridge, and with nearly a dozen other cities in an ongoing study.

They corralled historic aerial photos from university map libraries, and more recent images from the U.S. Geological Survey. The pictures, the earliest of which date to the 1950s, reveal a history of whole cities slowly consumed by parking lots. The photos have also enabled McCahill and Garrick to come up with some pretty precise numbers of total parking spots in each town.

"When we show people that we’ve actually been counting parking spaces," McCahill says, "anybody who’s sort of interested in this idea gets really excited because it hasn’t really been done."

Of course, it hasn’t been done before because no one wants to do this.

"It’s not that I wanted to," McCahill says, laughing. Each city took about 10 hours. (Also, this is what undergraduates are for.)

The results add some hard data to the public debate around parking spaces—how many are really needed per vehicle and how much they aid or deter development. McCahill's maps don’t include on-street parking, or underground parking that’s concealed from above by other structures. The researchers also made some calculations about the average height of parking garages in each city.

That said, they counted 21,690 parking spots in New Haven in 1951. By 2009, the number was 106,410. Hartford, meanwhile, went from about 47,000 spots in the mid-1950s to about 141,000 today. All the while, both cities lost considerable population, while the number of parking spaces per driver doubled.

These trends speak to a conventional wisdom that more development, more businesses, more people—more of anything—should always come with more parking.

"The idea, especially in these cities surrounded by suburbs," McCahill says, "[has been that] if we want to compete with the suburbs, we need to make sure that every successful business has enough parking so that people don’t have to weigh that in deciding whether they’re going to go into the city, or go into the suburbs where parking is free."

Cambridge offers an alternative view of the path not taken by Hartford and New Haven. That city has grown in population, and it actually has fewer parking spots today than it did in 1985, thanks to parking maximum regulations that go back more than 20 years and to aggressive planning for alternative transportation.

There is, however, no causal relationship here. Removing parking lots in Cambridge did not necessarily prompt new residents and businesses to flood in. But Cambridge goes against the planning theory that all of these numbers must rise in tandem. 

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