SAN FRANCISCO (CBS SF) – The Twin Peaks Tunnel, which has been closed for the past two months undergoing major upgrades, reopened to serve three light-rail routes Saturday, with a fourth service set to resume Monday, the San Francisco Municipal Transportation Agency said today.

The tunnel connects Muni’s Castro and West Portal stations, and light-rail trains on the J-Church, K-Ingleside and M-Ocean View lines are again operating normally as of today.

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“Everything is running smoothly today,” Muni spokesman Paul Rose said.

Set to return Monday is the Nx “Judah Express” bus service, a companion express service to the N-Judah rail line service.

Since buses don’t use the tunnel, construction didn’t directly affect the Nx service. But Rose said that the tunnel’s closure made necessary some Muni shuttle-bus services, which took drivers away from the Nx. With the tunnel now open, the drivers who piloted the temporary shuttles are now freed up to return to their previous Nx bus routes, Rose said today.

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Trains on the N-Judah line do not use the Twin Peaks tunnel, Rose said.

The 100-year-old tunnel’s infrastructure, including the tracks, walls and drainage systems, have been upgraded, and seismic reinforcement are expected to better protect the tunnel’s overall structure and stability.

Four new track crossovers were installed in the tunnel to allow trains to switch tracks and avoid delays at stations near the tunnel. The new tracks mean the tunnel’s previous speed restriction will be lifted.

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The tunnel project wasn’t without its controversies. On Aug. 10, construction worker Patrick Ricketts was killed when a falling steel beam near the West Portal end of the tunnel hit him. It was then discovered that his employer, Shimmick Construction of Oakland, had a history of workplace and safety violations, including one involving a November 2016 fatality.