Lanes south of Market Street on a busy section of Fourth Street between Bryant and Harrison streets are being shut down so construction can begin on the central subway project.
It might look like digging, but the San Francisco Municipal Transit Agency says it's just prep work.
"This is preparation for digging; we'll have cranes next week that will dig for the launch box digging, which will be much deeper and wider," SFMTA spokesperson Paul Rose said.
The "launch box" is a 50-by-500 foot box to accommodate two tunnel digging machines with 41-foot diameter drills that are 312-feet long.
It will take about two years to drill the 1.6 miles from Harrison Street to North Beach. The project is expected to cost $1.6 million and open in 2019.
"At some point they'll descend almost 90 feet underground just to pass underneath the existing BART and Muni metro lines at Powell Street," Central Subway Project spokesperson Brajah Norris said.
The central subway will ultimately run from Fourth and Brannan streets to Chinatown with four stations along the way. It links with the existing T-Third line, which taken together form a continuous transit line north-south across the city.
But there will be plenty of inconvenience between now and then. The busy intersection, with a southbound Highway 101 on-ramp, will lose two lanes for the next two years or so.