Nearly two dozen Port Authority transit routes will be affected by a track replacement project at the South Portal of the Mt. Washington Transit Tunnel set to begin Friday evening, the transit agency announced.

Starting at 7 p.m., the Mt. Washington Transit Tunnel will be partially closed to light rail traffic from South Hills Junction to Station Square Station.

The tunnel will close to all busway traffic from the Palm Garden Ramp and Stop to Station Square Station.

The work involves replacement of about 480 feet aging light rail track and busway pavement.

The Lower Haberman Busway Ramp also will be closed during the project, which is expected to last until late August. Inbound light rail vehicles will travel by street tracks through Allentown. The outbound rail line will continue to use the remaining active track in the transit tunnel.

During the day, inbound buses will use the Wabash Tunnel and outbound buses will follow a detour through Allentown.

Rail cars will be able to use the tunnel in both directions after 11 p.m.

Here are the routes that will be affected during construction:

• 39 - Brookline

• 41 - Bower Hill

• Y1 - Large Flyer

• Y45 - Baldwin Manor Flyer

• Y46 - Elizabeth Flyer

• Y47 - Curry Flyer

• Y49 - Prospect Flyer

• 43 - Bailey

• 48 - Arlington

• 51 - Carrick

• 40 - Mount Washington

• 44 - Knoxville

• 51L - Carrick Limited

• RED - Castle Shannon via Beechview

• BLLB - Library via Overbrook

• BLSV - South Hills Village via Overbrook

• RED - South Hills Village via Beechview

• RED - Castle Shannon via Beechview

• BLLB - Library via Overbrook

• BLSV - South Hills Village via Overbrook

• RED - South Hills Village via Beechview

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