Santiago Calatrava’s centrepiece of the sprawling new transit facility at the World Trade Center complex in New York will open on Thursday (March 3).

The World Trade Center Transportation Hub, also knows as the Oculus, represents the most integrated network of underground pedestrian connections to mass transit lines in the city, and doubles as a light-filled public gathering space and retail zone. The building has taken 12 years to build at a reported cost of US$4.4bn (€4bn, £3.1bn).

Inspired by the image of a bird released from a child's hands, Calatrava has designed the hub as a large elliptical volume of glass and steel ribs extended to create canopies over a plaza.

Two 350ft (106.6m) arches flank the project's central axis, and between them rests a 330ft (100.5m) operable skylight which frames the New York sky. This will open on warm days and annually on 11 September, flooding light into the building in tribute to those who lost their lives in the 9/11 terrorist attacks.

“The combination of natural light and sculptural form give dignity and beauty to the building’s lower levels and pedestrian walkways, and provide New York City with a kind of public space it has not previously enjoyed,” said Calatrava – who was last year awarded the European Prize for Architecture.

“The first major design decision was to conceive the building as a freestanding structure and situate it along the southern edge of Daniel Libeskind's 'Wedge of Light' plaza,” he added.

“This treatment of the site creates a kind of pause amid the dense commercial towers and links the procession of green spaces extending from City Hall Park to the churchyard of St. Paul's, through the WTC Transportation Hub plaza to the gardens of the Memorial and Battery Park.”

The hub was commissioned to replace the original Port Authority Trans-Hudson (PATH) rail system, which was destroyed on 9/11. It will ultimately provide street-level access to the 9/11 Memorial and Museum and below-ground access to One World Trade Center, 3 World Trade Center, 4 World Trade Center and 2 World Trade Center.

“This was a challenging project for the agency in terms of timetable and costs, but the men and women of the Port Authority and the contractors who worked on this nationally important infrastructure project should be rightly proud of their efforts,’’ said Port Authority chair John Degnan. “We trust the Oculus will serve a vital transportation need for the region, while becoming an important landmark for the metropolitan area and nation in the decades to come.”