Although the Midtown office market appears to be improving, many real estate executives expect vacancy rates to rise downtown as companies like Goldman Sachs, Merrill Lynch, Nomura and A.I.G. move to new locations or shrink. “Downtown is a much more volatile and fragile market than Midtown, because of the overhang of large tenants with expiring leases,” said Robert L. Freedman, executive chairman of the commercial real estate company FirstService Williams.

The long-simmering dispute pitted Mr. Silverstein, backed by Mayor Bloomberg and Assembly Speaker Sheldon Silver, against the Port Authority and the governors of New York and New Jersey.

The two sides were barely on speaking terms when Mr. Silverstein, chief executive of Silverstein Properties, or S.P.I., took the matter to the arbitration panel in August. He claimed that long delays by the Port Authority in rebuilding the infrastructure at ground zero had undermined his ability to attract tenants and get the financing. He asked the panel to rule that the Port Authority had breached its obligation, and he sought 10 years of free rent and a declaration that the authority had violated the development contract, opening up the possibility for up to $2.75 billion in damages as a remedy.

But the arbitrators ruled that Mr. Silverstein “has not shown that any action or inaction” by the Port Authority to date “has actually delayed or damaged S.P.I. in its construction of the towers.” Indeed, the arbitrators said that witnesses for Mr. Silverstein acknowledged that construction of the towers could proceed “if the funding problem did not exist.”

The arbitrators did say that the Port Authority performed inadequately in 2006 and 2007 in meeting its obligations under the development agreement. But since Christopher O. Ward became executive director of the Port Authority in 2008, the arbitrators said, “much has changed, contracts have been let, and the infrastructure work is moving head.”

“Meanwhile,” they said, the Port Authority “has invested or committed over $2.3 billion to redevelopment of the site.” They also said the authority had made “significant concessions and adjustments” for Mr. Silverstein. At the same time, the panel left open the possibility that Silverstein Properties could be entitled to “possible ground rent damages” in the future.