PITTSBURGH—Light-rail trains are again serving all downtown Pittsburgh subway stops after a derailment limited service since Friday night.

The Port Authority of Allegheny County says it has determined why the train derailed near the Wood Street station, but won't be commenting on that until the agency discusses the matter with state investigators later this week. Three passengers complained of minor injuries after the incident about 9 p.m.

The derailment kept trains from running to and from some downtown stops and those on the North Shore, near the city's pro sports stadiums, PNC Park and Heinz Field, and the Rivers Casino.

But that service had been restored by the Monday morning rush hour and was not expected to affect fans who planned to use the trains to get to and from Monday night's Pittsburgh Steelers game.