The Port Authority has announced the detours that will be in effect over the next three weekends while three Fort Duquesne Bridge ramps are closed near Heinz Field for light-rail construction.

The closings will begin at 10 p.m. tomorrow and be lifted no later than 6 a.m. Monday. During that time, workers will transfer the weight of the elevated ramps from existing foundation piles onto reinforced concrete slabs and columns to provide space for tunnel construction.

The ramps lead from the North Shore near Heinz Field to the bridge, and from the bridge to and from Route 65/Ohio River Boulevard.

The Route 65 mainline between the West End Bridge and the North Side/Interstate 279 will remain open, as will ramps between the Fort Duquesne Bridge and I-279.

Detours include:

Route 65 to Downtown

Use the West End Bridge to West End Circle to West Carson Street and travel inbound on the Fort Pitt Bridge.

Route 65 to Parkway West

West End Bridge to Route 51/19 south to the Parkway West/I-279 south.

Parkway West to 65 or North Shore

Exit to Route 51/19 north just before the Fort Pitt Tunnels. Use the West End Bridge to Route 65 or the North Shore exit.

Parkway East to 65 or North Shore

Use the Fort Pitt Bridge and exit onto West Carson Street. Continue via the West End Bridge.

Fort Duquesne Bridge to 65 or North Shore

Follow I-279 north and take the Route 28 north/Chestnut Street Exit. Turn left at Madison Street, again at East Ohio Street and again at I-279 south.