When the City of Anaheim launched a design competition in 2009 for a new transit hub, city leaders wanted an iconic structure. In the Southern California home of Disneyland, itself a celebration of mobility and fantasy, the Anaheim Regional Transportation Intermodal Center, or ARTIC, is a soaring, optimistic expression of the potential for public transportation in this capital of car culture.

Though the ARTIC now serves passengers of the region's Amtrak and Metrolink trains, as well as local and regional bus lines, it will also accommodate the long-intended but still unpredictable plan to bring high-speed rail through California. “One of the key tenets of transportation architecture is that you have commuters using the building regularly, but also people who will pass through it only once,” says Ernest Cirangle, FAIA, the Los Angeles'based design principal. “The building needs to be very clear, intuitive, and simple in terms of the flow of people.”

That flow of people comes from all sides of the building. On the north, a parking lot transitions into a shared pedestrian and driveway space leading to the main entrance, a 120-foot-tall cable-hung glass curtain wall that allows views both into the main public hall of the center and, once inside, views north to the San Bernardino Mountains. Tapered, vertical box-section steel girts on the inside wall support the glass with custom armatures, resisting lateral loads like wind, while the tensioned-cable system supports the dead loads of the glass. A similar system supports the south facade's glazed curtain wall. Both curtain walls feature glass louvers for mixed-mode ventilation, part of the environmental strategy the design team is counting on to achieve a LEED Platinum target.

On the ground floor, ticket booths and a convenience store form the backdrop for casual tables and chairs scattered across the terrazzo floor. Doors on the east and west provide access to bus stops on either side. Escalators in the center lead to a second level that will eventually feature full-service restaurants. Another set of escalators takes visitors to the third level, or mezzanine, which features small waiting rooms. From there, passengers can walk outside across a covered bridge to the train platforms. The soaring shell structure provides the space, daylight, and views to the outside that allow for clarity and continuous wayfinding.

Only on the underside of the shell does the glistening form of the building start to reveal its construction, as the steel tube arches organized in a diagrid pattern appear like a space-age version of the ribbed vaults in a Gothic cathedral. The steel girts at the curtain walls also stiffen the arches, acting somewhat like spokes on a bicycle wheel to prevent the arches from deforming.

Inspired by great transit halls of the past as well as the historic hangars for dirigibles found throughout Southern California, ARTIC takes its form from a catenary arch rotated to form a torus and then cut. Bruce Gibbons, the building's structural engineer and managing principal of Thornton Tomasetti's Los Angeles office, investigated several technical solutions for the building to find the most efficient, simplest shape. “It's like a doughnut with a catenary section. Then we took a small bite out of it and that resulted in the pure shell,” Gibbons says. Buttresses concealed in metal cladding connect the shell to the ground. A combination of shop and field welds connect the individual steel members forming the arches.

The integration of the facade structure and the arch structure emerged from Gibbons's early involvement in the competition phase. At that time, the design team quickly settled on the use of ETFE as the main enclosure system for the shell due to the benefits of the material's light weight and daylighting characteristics. The ETFE pillows forming the envelope consist of three layers, with an approximate 75 percent frit on the outer layer and then two constantly pressurized internal cavities created on either side of the middle layer. Kurt Komraus, the facade consultant for the project and an associate at the Los Angeles office of Buro Happold, detailed the envelope from the model drawings and performance criteria Thornton Tomasetti had developed through the design development phase. “Distilling the software model geometry down to 9,000 data points gave the whole team a common language for locating our systems,” says Komraus.

The ARTIC's ETFE pillows take complex forms to match the arch's curves. Each pillow is sized differently, with slightly smaller bottom layers to prevent puckering under tension. Rectangular steel “stools” welded to the top of the arch's tubular members provide the platform for a two-layer aluminum extrusion for clamping the edges of each pillow, while also forming a stormwater gutter system on the exterior.

Although it's not the first project to use an ETFE cladding system in Southern California, the sleek, comfortable quality of the great hall has become its own tourist attraction. The City even touts it on billboards around area freeways. It's not uncommon to see a family of bicyclists make a detour from the public path along the adjacent Santa Ana River to check out the building and find that, unlike the area's other attractions, it's free to enter.