Santiago Calatrava, design architect and a structural engineer, has been working on the World Trade Center Transportation Hub, along with the Downtown Design Partnership, for three years. Nadine M. Post, ENR’s editor at large, interviewed Calatrava on the project and on his feelings about design as well as working in the U.S.
ENR: How do you feel about living in New York City and working on the World Trade Center Transportation Hub for the Port Authority of New York & New Jersey?
Santiago Calatrava: I came to the U.S. because I liked the country and for the experience of living here with my family. (My children are getting educated here.)When I moved to the U.S., I was more than 50 years old. It was just for pleasure. I wish to be more a part of the overall happening in the U.S.
There are aspects of working on the transportation hub that I like. There is enormous team work. I like the atmosphere of a body of people working for a goal. The other thing I like is the enormous challenge of building the station. The enormous scale of projects in New York City is a problem. American society grows by challenge. I am experiencing that with the port authority. I have been working with the port authority for three years. It is very intensive. An extraordinary opportunity—working with the port authority and my partners trying to make the project better. We never stop.
Finally, money is an important issue all over. We have to provide cost-effective construction and not cheap construction. Are we doing cheap engineering or cost-effective engineer? Even the most cost-effective structures have had a certain moment for emotions and for the grandeur of the moment. Look at the Golden Gate Bridge. This is also America.
It is important to keep alive the flame. Buildings are not only purely functional but part of the heritage for the next generation. We know these structures add value and are emotional. It is very important.
The transit hall, with its movable roof, becomes a “sign” for a station that is unique to the area. It’s movable roof is part of this. The glass and the opening will let in light. The code calls for an opening for smoke exhaust and ventilation. I can do several openings in a roof or a single one. A single opening is a pragmatic approach but it can also have a very beautiful symbolic aspect. A single opening offers a piece of the sky of Manhattan. The whole building responds to an idea and catches the attention of people. It is beyond the pure pragmatic. There is a symbolic value that goes beyond us and delivers a message to the next generation. It becomes a landmark. It is important to recognize this capacity if the architect is to go beyond the pure pragmatic.
ENR: How would you describe the design for the World Trade Center Transportation Hub?
Calatrava: The World Trade Center Transportation Hub is primarily comprised of two naturally illuminated spaces, the Transit Hall and the PATH mezzanine.
The transit hall contains two retail concourses approximately 25 ft and 45 ft below grade. The lower concourse forms a 340 x 180-ft elliptical commuter mixing bowl, offering connections to the Fulton Street Transit Center; the #1, R, W and E subway lines; and all points north, south and east.
As the only portion of the project above ground, the operable roof of the Transit Hall is the symbol of the Hub. The backbone of the roof is defined by two pairs of parallel steel arches. Each pair has an upper “operable” arch and a lower “fixed” arch. The arches span 340 ft and rise 120 ft above the plaza grade. The fixed arches are supported by steel portal frames, or ribs, spaced 5 ft 6 in. on center around a 340 x 111-ft ellipse. The operable arches spring from four bearing points located in pairs at the east and west abutments. A tension ring at grade restrains the dynamic lateral forces of the ribs and arches within the transit hall. Steel rafters ranging in length form 30 to 180 ft cantilever from the operable arches and form asymmetrical winged canopies over the plaza. During the day the roof structure allows natural light to flood the transit hall. At night, the illuminated building becomes a lantern for the surrounding area. On temperate days, and annually on Sept. 11, the roof will open approximately 30 ft at its zenith to allow natural ventilation and a slice of the sky into the building.
West of the Transit Hall, an 80-ft-wide grand stair descends 12 ft to the PATH mezzanine, which houses the paid fare zone for the PATH transit system. The train platforms are located 16 ft directly below the mezzanine and are visually and spatially connected to the mezzanine through large openings in the floor. The PATH mezzanine is a large, column-free trapezoidal space defined by undulating concrete arches. These arches are spaced 5’-6” on center and modulate in depth from east to west to form the roof structure. They are supported by two 170-ft- long concrete box girders that also function as supply and return air plenums. A glazed roof, which also forms a plaza above, allows natural light to filter down through the concrete arches, the mezzanine and onto the train platforms.
ENR: What is the intent of the design?
Calatrava: I had felt from the beginning that the design of the new transportation hub was a very important project, because it has the potential to create a kind of living memorial at the World Trade Center site. It would be very beautiful, if people were to come to this place of remembrance through a setting full of light and activity.
A great many people will use the transportation hub every day—coming and going from their jobs, visiting the cultural sites, and of course coming to the Memorial. I hope they will feel, as I do, that the structure is built with columns of light, and that they will look forward to the moments when the roof actually opens to the sky.
ENR: What was the inspiration for the design?
Calatrava: The image that emerged, as I thought about this design and what it must express, was of a child opening her hands to release a dove into the air. Of course, this image cannot literally be read in the building. The form might also suggest motifs from many traditions: the Byzantine mandorla, the wings of cherubim above the Ark of the Covenant, the sheltering wings on Egyptian canopic urns. But I believe the gesture is there—the movement of something being opened to the sky and becoming free.
ENR: Did you draw on any of your other work, for example the TGV station in France?
Calatrava: I have found that every project you build poses problems that can be solved only by the next project. This is why my designs often develop as a series. First the arch of a bridge is positioned here, and then there. Or, for a tall building, first the floor slabs are cantilevered off the core in this way, and then in another way. So, for the World Trade Center Transportation Hub, I carried forward ideas I had begun to explore in earlier projects, such as the Lyon Airport Station, or Stadelhofen Station in Zurich. I feel it is very fortunate that I had these earlier ideas to draw on, because the function of the transportation hub is so complex, the site is so dense, and the need for symbolic expression is so great, that I have had to call on every bit of my experience.
ENR: How did the original WTC and 9/11 figure into the design, either directly or indirectly? How about the site, neighborhood architecture, population?
Calatrava: The first major design decision was to conceive of the building at street level as a freestanding structure. It will be situated within the landscaped Wedge of Light plaza (approximately 410 x 205 ft) that has been described in Daniel Libeskind’s master plan for the site. The building is angled to sit along the southern edge of this plaza. Among its principal benefits, this treatment of the site opens a quieter space—a kind of pause—amid the dense buildings that are planned for Ground Zero and creates a link in a procession of green spaces, which will extend down Park Row from City Hall Park to the churchyard of St. Paul’s, then through the WTC Transportation Hub plaza to the Memorial.
ENR: Did constructibility fit into the design, and if so, how?
Calatrava: The transportation hub is a utilitarian building, and so constructibility and functionality are always very, very important. For example, we have to create links to many other buildings: the WTC Memorial, Freedom Tower, the Fulton Street station, the corridor to Liberty Plaza. To make those links function well, we have to go through a very rigorous design process in collaboration with the port authority.
This is not a building in which you can see a problem in the design and correct it in isolation. This building is a system in which, when you touch one thing, all the other parts move. The consequences play out not just here, but there, and there, and there. Even so, we have not been shy about readapting the scheme. The challenge has been to use each so-called difficulty to improve the architecture, to make it more coherent, so that this utilitarian building will also be very beautiful.
ENR: Compare working for the port authority with museums or cultural clients.
Calatrava: I had dreamed for many years of working in New York for the Port Authority. The most magnificent of the city’s suspension bridges—the George Washington, Bronx-Whitestone, Throgs Neck, and Verrazano-Narrows—were all designed for the port authority by Othmar Ammann, who was educated at the Federal Institute of Technology in Zurich, the same school where I studied civil engineering and earned my doctorate.
Now that I am working with the port authority, I understand that its sense of professionalism has a lot to do with its being such a stable institution. The project may therefore appear to the outside world to be proceeding very slowly and quietly, as if nothing much was happening. But in fact we have been working continually on the scheme, to make adjustments as the program evolves and to meet the port authority’s target dates. With a museum or cultural building, by contrast, there might be more peaks and valleys of activity, and the public might be more aware of them.
ENR: Compare this commission with others.
Calatrava: Because of the nature of the project and the significance of the site, I don’t think the World Trade Center Transportation Hub can be compared to any other commission.