Crews finish building tunnel for Central Subway line

SAN FRANCISCO (KGO) -- The digging is done on the tunnel that will house San Francisco's Central Subway line. This project will extend Muni's T Third light rail line from its current terminus, at Fourth and King Streets, through the South of Market area, Union Square, Chinatown, eventually ending at Stockton Street and Washington Street.

On Monday, the media got to take a look at the progress of the 1.7 mile, new subway line which has cost $241 million to build. People aren't supposed to walk in the subway tunnels of course, but the tracks haven't been laid down yet.

In 2019, San Francisco's light rail T line will be running through this tunnel and another just like it. San Francisco Mayor Ed Lee was at the event, along with many of the people who help design and build these projects.

On-site engineer Munn Leong admitted he has spent more time underground than he has at home. Leong a Concord resident, and father of two, who has helped turn plans into concrete. He's been on this project since 2012.

Program director John Funghi has been working on this project since 2006. He told ABC7 News he thought it was quite peaceful underground.

The bore has an S-curve and elevation changes. The bore has a diameter of roughly 18 feet on the inside, with the concrete measuring 11 inches thick.

Tunnel people take certain parts of the job for granted. The tunnel is 1.7 miles and at one end, they had to hit a bullseye, four-inches wide and they say they were on the button, within an inch.

It's an achievement most passengers will never consider when traveling through the tunnel for the next 100 years, and probably more. Among these riding the line will likely be Leong's kids Emily and Ethan. He brought them to the site one day and they said they thought it was cool that their dad builds tunnels.

This will be another ho-hum, out of site and mind, engineering marvel beneath the city.