The San Francisco Central Subway project reached a milestone Monday when crews completed a tunnel that will allow trains from the 4th and Bryant streets area to travel into Chinatown.
The tunnel is key to connecting Muni's T Third Line from South of Market up to Chinatown and eventually North Beach at Washington Square.
"The tunnel itself is constructed and finished, which makes today about the halfway point," San Francisco Mayor Ed Lee said.
John Funghi, the tunnel project director, said trains are projected to start testing in mid 2018, with full service expected to be available by January 2019.
The tunnel is made up of 1,750 reinforced concrete rings -- each one numbered and bolted into place.
City leaders tout the project in helping alleviate San Francisco's congestion and traffic issues. The project took about a year and cost $241 million.