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Anatomy of a Public Space

Anatomy of a Public Space
University City District

To the untrained eye, The Porch outside of Philadelphia's 30th Street Station has been an unambiguous success. Two years ago, traffic engineers paved over a lane of roadway in front of the train station, creating a broad sidewalk 50 feet across and 565 feet long. With about a quarter of a million dollars, the University City District organization then put out some tables and chairs, planters and umbrellas, none of it even bolted to the ground.

Since then, the space has become a popular plaza somewhere in between a pop-up park and a permanent icon like nearby Rittenhouse Square. People read books slouching in the bistro chairs. They take their lunch on The Porch. They come for the food trucks.


University City District

But this passing assessment – people seem to be using this public space – barely gets at the real question of urban design: How are they using it?

For the most part, this is just a particularly nice, rather large sidewalk.

"But there are choices," says Seth Budick, the policy and research manager for the University City District. "There are a lot of choices people can make. They can decide to sit in the sun or in the shade, they can decide to sit on any one of three or four different seating elements, they can decide how to move through the space. And that’s really what we’re looking at, that’s the interesting question about a lot of urban design: What factors in the environment impact people's choices?"

In other words, how do you create a space that can be experienced at two speeds – one for commuters dashing to catch a train, and the other for readers who want to linger? How do you design a plaza that feels spacious enough during the lunchtime rush but that doesn't seem empty in mid-morning? And what do Philadelphians really want in the city's "front porch": a seat in the middle of a buzzing crowd, or a private perch to people-watch from the periphery?

UCD's plan all along was to go light and flexible, and then study what happened next. The results so far, corralled in a report prepared with Interface Studio, yield an insanely intricate picture of one block of space: how people walk through it, where they prefer to sit, what role shadow plays.

That above diagram gives you the basic layout of the space, which is gently divided into a series of little "rooms" by the trees. The site has a full-time concierge who oversees everything (the plaza is also home to farmer's markets, yoga classes, concerts and other programming). In the course of constantly walking around, he helped collect data in the spring and summer of last year with this survey tool noting the weather, a pedestrian's location in the plaza, his or her rough age, whether he had luggage and stopped to read an informational sign, or used a cell phone:

That is, in short, how the amorphous science of public space produces quantitative data. Between April and October of 2012, this user census collected data on 24,698 people. Separate data collection tracked 290 lunchtime users (only 0.5 percent of them left any litter behind), and directly surveyed another 388 people on where they'd come from (94 percent arrived on foot, bike, or mass transit).

One of the resulting diagrams at top illustrates the flow of pedestrian traffic through the plaza – people tend to gravitate toward its western end – with the red dots capturing stopping points. Different stretches of the porch were also frequently used for different purposes, with people seeking solitude more often at the quieter eastern end:

Noise levels measured closer to busy Market Street were 10 times louder than those along Little Market Street immediately adjacent to the station – a partial explanation for why people tended not to linger there. The louder noise (70-75 decibels) was akin to a vacuum cleaner in your living room, the quieter sound (60 decibels) more like a conversation at close range.

One of the most elegant diagrams, at right, shows people increasingly shifting into the plaza's shade as the temperature warmed up over the course of the summer.

That discovery probably won't surprise anyone. But all of this data – even the data that supports intuitive design – is arguably important in creating public space when there's little money to work with. If you can only afford some lighter interventions, you can at least ensure they serve exactly how people move through and use public space.

"In the office, we started looking at pictures of Bryant Park, of Rittenhouse Square, and fantasizing about what [this] could be," says Prema Gupta, the director of planning and economic development for UCD, recalling the earlier stages of the whole project. "It's almost like there was a fork in the road. We could have built out that vision at that point, and we would still be fundraising for it, and it would still be a blank stretch of sidewalk."

Instead, UCD is learning that a farmer's market doesn't quite work here, but a food truck rally does. Bistro chairs are nice, but Luxembourg chairs are even better. Also, no wants to relax right in the middle of a pedestrian highway.

"I think the analogy that is interesting to me is to look at it like a website, look at it like Facebook," Gupta says. "I’d say our goals are similar to Facebook's goals: We want as many people as possible to use the site and stay for a long time and have a meaningful experience. And think of what Facebook looked like a couple of years ago. It's constantly evolving, tweaking, changing."

All graphics courtesy of University City District and Interface Studio.

Emily Badger is a former staff writer at The Atlantic Cities based in Washington, D.C. She now writes for The Washington Post. All posts »

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