SAN FRANCISCO (CBS SF) — After 100 years of helping to transport commuters daily from San Francisco’s West Portal neighborhood to downtown, the Twin Peaks Tunnel is getting a much-needed makeover.

And it’s much more than just slapping on a little new paint and replacing a few old light fixtures. The San Francisco Municipal Transportation Agency is replacing everything inside the tunnel — tracks, drainage system, the covering on the walls and giving it a seismic retrofit.

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SFMTA Director of Transit John Haley calls the 2-mile-long tunnel “the heart of the (Muni Metro) system.” Over 80,000 commuters travel through the tunnel each days as they travel from San Francisco’s western neighborhood to downtown.

The transit agency took advantage of a Memorial Day weekend shut down of the tunnel to give the media a look inside on Monday.

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“You heard a lot of grinding and that’s to take down some old concrete that’ll be ready to reinforce with a new concrete again for the next hundred years,” Haley said.

Transit officials are shutting down the tunnel for 60 days from June 25 to August 24 to work on it.

For two of the lines that run through the tunnel – the L-Taraval and the M-Ocean View – buses will replace regular Muni metro service and K-Ingleside line will operate along a modified route for the 60 day shutdown.

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“(The project is) about making sure that the structure is safe for the next generation and then generation after that,” Haley said.