The closure is required for the removal of the bridge floor beams, guardrails and deck.
The provincial government is investing almost $81 million over three years to modernize and strengthen the 53-year-old structure.
More than 100 signs have been posted in and around the capital region to inform motorists of the closure and of alternate routes.
To alleviate traffic congestion on the Westmorland Street Bridge in Fredericton, motorists are encouraged to use the Department of Transportation’s park and ride service from Brookside Mall to downtown Fredericton, the 15 park-and-go locations, and the local trail system to bike or walk. Drivers are also urged to carpool, adjust their travel times and use flexible work schedules.