Transit riders in Downtown Pittsburgh and the South Hills could face substantial delays this weekend because of two Pittsburgh Regional Transit projects.

The work, which involves concrete repairs inside the light rail tunnel between First Avenue and Steel Plaza and installation of fiber-optic cable along the Red Line on the light rail system, will begin at 11 p.m. Friday. It is scheduled to be done by the start of service Monday morning.

In the Downtown area, inbound service on the light rail system will end at the First Avenue Station. A shuttle bus will take passengers to the Steel Plaza Station on Grant Street, where they can get back on the light rail to continue their trip.

Outbound passengers from the North Shore and Downtown will get off the light rail at Steel Plaza and take a shuttle to First Avenue to get back on a train if they are continuing to the South Hills.

In the South Hills, outbound Red Line vehicles will be detoured to the Blue Line between South Hills Junction and Washington Junction. Inbound service will not be affected.

Riders between Allegheny Station and South Hills Junction, and traveling to stations on the Red Line between South Hills Junction and Overbrook Junction, should board any outbound rail car, disembark at Willow, and take an inbound Red Line rail car from Overbrook Junction to their destination.

The authority will operate a late-night rail shuttle between Washington and South Hills junctions. The shuttle will operate Friday evening until 2 a.m. Saturday; from Saturday evening until 1:40 a.m. Sunday; and on Sunday evening until 11:40 p.m.

Additionally, no buses will be allowed to use the Mount Washington Transit Tunnel, and the South Busway will be closed from Whited to Station Square. As a result, South Busway stops from Edgebrook to Station Square, including Pioneer and Dawn, will be out of service.

Inbound buses will detour through the city’s Allentown neighborhood. Outbound buses will use the Wabash Tunnel.

Ed covers transportation at the Pittsburgh Post-Gazette, but he's currently on strike. Email him at eblazina@unionprogress.com.

Ed Blazina

Ed covers transportation at the Pittsburgh Post-Gazette, but he's currently on strike. Email him at eblazina@unionprogress.com.