The Freedom Tower

The New York Times says that when one architectural ambition after another was given up at ground zero for economy, security and politics, it seemed that the architect Santiago Calatrava’s vision of a luminous, cavernous World Trade Center Transportation Hub would be immune from major change.

No more.

With the Port Authority of New York and New Jersey seeking significant savings in the budget and the timetable of the trade center reconstruction, a key element of Mr. Calatrava’s design —a vast underground mezzanine free of columns — may be in jeopardy.

Estimates vary on how much the projected cost of the transportation hub currently exceeds its $2.5 billion budget, but it could be at least several hundred million dollars.

Spanning great spaces without the interruption of columns is certainly possible and, all else being equal, aesthetically desirable. But it also adds to the complexity of construction.

Two alternatives under consideration call for standard column-and-beam construction instead of the long spans and cantilevers proposed by Mr. Calatrava.

For his part, Mr. Calatrava says his design can be constructed on budget and on time, noting that there had already been revisions made to it without abandoning the columnless approach.

“It has always been my goal to deliver a beautiful, practical transportation hub for Lower Manhattan,” he said in a statement released by his office. “In its revised state, the project retains all of its fundamental beauty, and the adjustments make it an ever-more-functional and coherent facility that will serve New York well in the years to come.”

No version would eliminate the ribbed and winged roof over the hub’s arrival hall, east of Greenwich Street, which Mr. Calatrava has likened to a bird in flight. Keeping it would permit officials to assert that they had been faithful to the original architectural concept.

But it is the underground mezzanine, west of Greenwich Street, that will be the functional heart of the hub, occupying the level between the arrival hall and the PATH platforms. How it is treated depends in part on whether it is seen as a passageway through which commuters hurry or as a ceremonial gateway on the scale of the main concourse at Grand Central Terminal.

At the tightly squeezed trade center site, how the mezzanine is constructed has an effect on all the buildings around it. Directly above it would be one corner of the 9/11 memorial plaza. Adjoining it would be the lower level of Tower 3, a 71-story office tower being developed by Silverstein Properties. Running through it would be the tracks and station of the No. 1 subway.