Welcome back to New York. You've just returned from a year in Rome. What do you miss the most about Italy?

I was sad to leave Rome but I love being back in New York and working on the High Line again. The year was such a gift and it’s embarrassing because it makes it sound like I did not enjoy my time there, but I have not missed it at all.You were in Rome as a Prize Fellow at the American Academy in Rome, where you created Chance Encounter on the Tiber, an urban experiment involving 100 chairs and an unexpected musical performance on the Tiber River. Tell us about the project.

I spent a lot of time riding my bike along the abandoned walkways and embankments along the Tiber River. These walkways were built between 1876 and the 1920s to control the annual flooding of the river that would regularly inundate the city. Although the embankments have served their purpose of protecting Rome, for much of the year the walkways are essentially unused by Romans and visitors alike.

The site reminded me of my early experiences as one of the co-founders of the High Line project. I realized that making the walkway into a vibrant social open space didn’t have to be difficult, complex, or expensive. An alternative to grand architectural and urban planning schemes would be to focus on two simple issues: seating and programming. I wanted to try an experiment: place 100 movable park chairs on the open space along the Tiber River and see what happens. Where did this idea originate?

I was inspired by William Whyte’s studies in The Social Life of Small Urban Spaces, in which Whyte found that one of the most successful tools in creating vibrant spaces was the use of movable chairs. One of his most memorable findings is that people create ownership of public space by being able to control where and how they sit in the urban environment.Can you tell us about your collaboration with Lisa Bielawa?

Another fellow, Lisa Bielawa, recognized the site as an ideal environment for her musical composition Chance Encounter, which was written expressly for performance in transient public spaces. The 35-minute piece is designed so that a chamber orchestra arrives from all over the city, ready to play, and it is not prescribed where and how the audience should or might sit to enjoy the music.

Over meals at the Academy, we discovered our shared fascination with this site. Independently of each other, we had both even started thinking about different projects at this same site, and since our perspectives were so complementary, we decided to create a project together: Chance Encounter on the Tiber.

On Sunday May 30 2010, there was a preview of our project at the opening of Rome’s new MAXXI Museum designed by Zaha Hadid, which was open to the paying public for the first time that day. MAXXI is the largest museum of contemporary art in Rome, and one of the largest new buildings in Rome in decades. In many ways, this space could not be more different from the Tiber River site – in a city whose public spaces are largely Baroque piazzas with Classical ruins in sight, Hadid’s building is a striking anomaly. When MAXXI offered the opportunity to try our joint experiment in Hadid’s piazza, we realized this was a chance to see how the project would unfold in two radically different urban settings. So much outdoor furniture is intended to fade away. Did you intentionally choose red to stand out?

I had originally intended to use the movable park chairs that one finds in public spaces all over the world, from the French manufacturer Fermob. I got a few samples in different colors and settled on red. On the High Line we use grey and Bryant Park uses green to blend in with the grass, but on the Tiber, I wanted them to stand out so they would catch people’s attention. Fermob could not deliver the chairs in time, so we found a similar black and brown chair at IKEA for a fourth of the price. To get a glossy, weatherproof finish, we had them painted at an auto body shop, using a color called Corso Rosso – Italian motorcar racing red. It made me want to have all my furniture at home repainted at an auto body shop.You staged the experiment in several different spots. Were the reactions/results similar or different for each of the locations?

On the morning of Sunday May 30, 2010, before MAXXI opened, we set up the 100 red chairs all over the sunny piazza, and as soon as people entered, they began moving the chairs into the shade. Throughout the day we watched the chairs follow the shade lines that the building and trees made. Unlike the Tiber, this site had abundant pedestrian traffic that allowed the chairs to work their magic: couples kissed, families created picnics, teenagers hung out and talked. The previous day at MAXXI, when the museum offered free admission to pre-registered guests, the piazza was only used as a backdrop for photos and as a way in and out of the museum. With the chairs, the space became an active communal space. Their glossy red color popped against the monochromatic white piazza and building.

The chairs helped enliven Hadid’s austere piazza, encouraging people to behave in ways that Romans behave in the more familiarly-styled piazzas of the city. On subsequent visits to the museum, we have noticed that the piazza tends to be deserted even when the museum is crowded.

The May 31, 2010 performance on the Tiber was informal and chaotic. People used the chairs in a broad variety of ways and set them in a variety of orientations – not always facing a group of musicians, but some in clusters or facing the water. On the periphery, people continued conversations or reading while listening to the music. They did not feel compelled to behave like a concert audience, but felt free to walk around and hear the piece from different locations within the space, which is really a wonderful way to hear the piece. People also gathered on the bridge and upper walkway, watching and listening from above.You are cofounder of the High Line, a project that also took an abandoned area and brought it to life. However, in Rome, you had far less time to turn this around. What was your biggest challenge last year?

Many people had told us that it is impossible to get anything like this done in Italy in the several months. We partnered with Rome-based the organization TEVERETERNO, which produces cultural events that promote the potential of Rome’s Tiber River to help us get approvals from a series of government entities. A large swath of the Tiber has been leased to a private events company to put over 100 vendors and restaurants on the walkway. We only discovered this setback three weeks before our event. It meant that not only would there be no room for our project, but several blocks would be entirely privatized with commercial activity. Balanced introduction of food and drink vendors can bring people to under-used urban areas. However, we thought that giving over the entire space to privatized bars, restaurants and shops is not the way to make a truly vibrant, open public space. In fact, many of these restaurants and street vendors actually block the view of the river.

While we are critical of their use of the space, the vendors themselves turned out to be incredibly generous. They agreed to hold off setting up their operations until June 1.

Although the walkways often flood for several weeks in the middle of winter, this has been one of the rainiest years in decades, and the Tiber started to flood the walkway again in April. Just a week before our project, it receded below the walkway. We were lucky to have a group of 15 enthusiastic volunteers who not only helped us move the chairs and music stands down the stairs, but undertook the unglamorous task of washing down the stairs.Your biggest surprise?Even before we had our final approval, we started testing chairs on the site. The biggest surprise for me was that the red chairs alone were not enough of a draw to attract people from the bridge and streets above down to the banks of the Tiber. We realized that the crucial difference between our site and many of the sites that Whyte studied was that his sites were high in pedestrian traffic but largely unused, whereas our site was unused but extremely low in pedestrian traffic. The chairs alone could not overcome most Romans’ preconceptions of the Tiber as an undesirable space. Sometimes bicyclists stopped and used the chairs to rest, or people ate lunch while sitting in them, or groups of teenagers would sit and smoke, but many chairs remained empty during the day. We always knew that both seating and programming were essential to this experiment, but this experience underlined the importance of the combination of the two. If the goal is to make a site into a vital public space, programming is needed to draw people into the space, and the chairs keep them there by making the space “sticky.”

The most common warning we heard from locals ever since I began talking about the movable chairs was that Romans would steal the chairs instantly, or throw them into the river, even though we planned to remove them at night. Even though the chairs were often unattended for the several days of testing and performance, not one chair went missing.

While working on this project with Lisa, the two of us realized that we had very different views of what we hoped would be the lasting impact of our project. I was less interested in what actually happened the performance days, and more interested in its potential impact on the way people design, use and organize public spaces. I was happy that people enjoyed the benefits of having the chairs – kissing, eating, reading – but his real hope is that it might inspire some kind of lasting effect on the Tiber or elsewhere. Where are the 100 chairs now?

On Sunday August 29, 2010 we had two performances of Chance Encounter on the opening day of the 12th International Venice Biennale of Architecture. TEVERTERNO sponsored a new set of 100 red chairs. The first performance was in the garden outside of the Italian Pavilion in the Arsenale and we had planned to have the second performance in the same location.

Earlier in the day I ran into Piet Ouldof, the High Line garden designer, who had been invited by the biennale curator to design a garden where the Arsenale meets the water. It looks like a slice of the High Line plantings transported to Venice. After Piet and our TEVERTERNO partners made some calls to the powers that be and 15 minutes before the second performance was supposed to begin, we moved the 100 chairs (with the help of many Biennale visitors) to Piet’s garden and had the final performance in Piet’s perennial garden.

Thirty of the chairs are now at the Fortuny Museum in Venice and we are talking about another set of them going to the Venice Guggenheim when they finish their renovations of their garden. MAXXI was so pleased with the project that Pio Baldi, the museum’s president, inquired about making the red movable chairs a permanent part of the piazza. MACRO Museo D’Arte Contemporanea Roma (another contemporary art museum in Rome) exhibited three of the chairs at the Festa dell’Architetura di Roma all summer and has made them part of their permanent collection.

Although we knew this project would not be permanent, I hope it may inspire the city of Rome to make the chairs a seasonal part of the walkways. TEVERETERNO and I are now in discussions with city officials about the possibility of having 1,000 movable red chairs on the Tiber next fall for over a month, possibly incorporating new music written just for Rome. All we need now is a sponsor to help underwrite it.You're now back at the High Line. What's next in store for that project?

I thought the High Line would slow down once we opened the first section of the park, between Gansevoort – 20th Street – I was wrong.

Friends of the High Line manages the High Line under a license agreement with the NYC Department of Parks & Recreation. That means the gardeners, maintenance workers, greeters, tour guides, and bathroom cleaners - they are our employees. So we are busy getting people to become members of Friends of the High Line to help us raise the essential private funds to make sure the park is maintained at the high standards we have all come to love.

This effort will grow next spring, when we double the length of the park by opening the next section, between West 20th Street and 30th Street. The new section has some of my favorite features of the project. For example, there is the Woodland Flyover, between West 25th and West 26th Streets, where the grated metal path rises eight feet above the High Line, carrying visitors though a canopy of magnolia and sumac trees.

When this section of the park opens, it will bring the public to the doorstep of the last section of the structure: the High Line at the rail yards. It is still privately owned, and we are busy trying to figure out how we can get public access to that section of the High Line as soon as possible.