Atop the Air Rights Garage on Tuesday, local and state politicians, business owners and community activists gathered to celebrate the Board of Aldermen’s unanimous approval of the Downtown Crossing project the day before — the culmination of a years-long legislative effort to push through New Haven’s largest urban development effort in generations.

Mayor John DeStefano Jr., U.S. Rep. Rosa DeLauro, U.S. Sen. Richard Blumenthal LAW ’73, developer Carter Winstanley, State Sen. Martin Looney, and Gateway Community College President Dorsey Kendrick all spoke at the event, which followed over 100 public meetings throughout the approval process. The $135 million Downtown Crossing project will replace sections of Route 34 with urban boulevards and erect a 10-story, 426,000-square-foot medical office tower within the 11 acres of reclaimed land. Aldermen voted unanimously Monday night to approve the zoning changes and the development agreement necessary to allow the plan to be implemented.

“For half a century, the highway divided the city and served as a reminder of the homes and businesses that were lost,” Destefano said, referring to the destruction of the Oak Street neighborhood to make way for an extension of Route 34 under former Mayor Richard Lee in the 1950s. “No more. This January, work will finally begin to remove the highway and restore the street grid, employing thousands of people and propelling our local economy for decades to come.”

The project’s timetable was also discussed at the event.

The first phase of Downtown project — partially funded by a $16 million federal TIGER II grant from the U.S. Department of Transportation — will focus on the project’s road construction work. Exits 2 and 3 of Route 34 will be closed, and the old Route 34 Connector at the North and South Frontage roads will be converted into an urban boulevard that officials hope will reconnect the Hill neighborhood with downtown. College Street will then be reconstructed at grade level.

In the project’s second phase, the city will transfer a 2.4-acre parcel to real estate development company Winstanley Enterprises, headed by Carter Winstanley. Winstanley will develop the site into a medical sciences office tower at 100 College St. with ground level retail space.

“The Downtown Crossing project is a model for how smart federal investment can spur job creation and make a city like New Haven a center of economic development,” Blumenthal said. “This exciting project is a model for making job creation grow from cutting-edge technology.

With $51 million in state aid, multinational drug-maker Alexion Pharmaceuticals has announced it will relocate its global headquarters to the new College Street tower by 2015.