On Friday morning, Pittsburgh Regional Transit announced that a crack on the light-rail track along Warrington Avenue was discovered once again. 

They said that the crack in the rail will disrupt their service on Saturday morning, but service will not be disrupted on Friday. 

This is the second time this week a crack has been found, but PRT said the one found today was not in the same location as the broken rail that was found earlier in the week. 

PRT said that light-rail vehicles will operate from the southern end of their lines, and that includes South Hills Village for the Red Line and Blue Line, and Library for the Silver Line, to South Hills Junction for the remainder of the day. There is also light-rail service from Station Square to Allegheny Station, which serves First Avenue, Steel Plaza, Wood Street, Gateway, and the North Side stations in between. 

Shuttles will be provided between the bus stop across from Station Square and South Hills Junction. PRT employees will be on hand to assist riders. 

Crews will begin work at the end of regularly-scheduled service on Friday night and are expected to be finished by mid-morning on Saturday. 

PRT added that the cause of the crack in the rail is unknown as of Friday morning. They did say that steel rails can contract and be more prone to developing cracks in colder weather.

This is a developing story.