The T-third line will run from Chinatown to Sunnydale, with four new stations in Chinatown, Union Square, the Moscone Center, and Fourth and Brannan streets.
Riders can connect to other light rail lines at the Union Square station.
You can check out the Central Subway later this month when it makes its debut with free, weekend-only service between the four new stations.
The long-awaited project's full-service will begin on Jan. 7.
RELATED VIDEO: Here's a sneak peek of SF's Central Subway in Chinatown
Here's a sneak peek of SF's Central Subway in Chinatown