Construction has begun on the Transbay Transit Center, San Francisco’s new multi-modal transportation hub designed by Pelli Clarke Pelli Architects. Scheduled to open in 2017, the glass-and-steel structure will connect the city and the Bay Area via 11 public transit systems. Conceived as “the Grand Central of the West,” the building is designed in the spirit of the great train stations of the world. The sustainable and accessible building is distinguished by dramatic light-filled spaces and a 5.4-acre rooftop park.

“We are very proud of our design for the Transbay Transit Center,” said Cesar Pelli, senior principal of Pelli Clarke Pelli Architects, whose design was selected in an international competition in 2007. “This will be a beautiful, functional and sustainable building for San Francisco.”

The project, which is being built on the site of the Transbay Terminal at First and Mission streets, will also spur development in the surrounding city blocks and anchor a new neighborhood.

“We are very excited about the civic mission of the Transbay project,” said Fred Clarke, senior principal of Pelli Clarke Pelli Architects. “We want this to be a great transit center—one by which the city is perceived—but it must also be a great neighbor.”

The Transbay Transit Center features an exterior glass wall with undulating forms like petals of a flower that architects say create a civilized presence on the street. These undulations also respond to the building’s robust concrete-and-steel structural system, which is engineered for performance in the event of severe earthquakes.

A public plaza on Mission Street marks the primary entrance to the Transit Center. The main public space, the Grand Hall, will be suffused with natural light. The central element, a 120-foot-tall “light column,” is a structural component that reaches from the park to the Lower Concourse. Topped with a 4,000-square-foot domed skylight, the light column not only supports the building, but draws daylight deep into the interior and frames views of the park above.

Architects say that as one of the country’s greenest buildings, the Transbay Transit Center will use multiple sustainable design strategies, including natural light. The building is targeted to achieve a Gold LEED rating.