The Dufferin Street Bridge, which crosses the Gardiner Expressway and rail corridor into Exhibition Place, is being closed to cars today for the next 18 months.
The bridge closure was prompted by an environmental assessment over the last year and a half that raised safety concerns.
Coun. Denzil Minnan-Wong, who also chairs the city's Public Works and Infrastructure Committee, said last month that the closure of the bridge is three years ahead of its original repair schedule.
Pedestrians and cyclists will still be able to use the thoroughfare, which will be replaced by three temporary bridges until the repairs are complete. A permanent bridge will be constructed sometime after 2016.
During the construction, the TTC will also be diverting the 29 Dufferin, 316 Ossington and 329 Dufferin bus routes.
The Dufferin Bridge was built in 1911.