SAN FRANCISCO — Drivers planning to use Highway 101 through San Francisco this weekend have a new complication to account for: Caltrans will now close one southbound lane as well as every northbound lane through Hospital Curve.
The closure begins at 11 p.m. Friday, Sept. 18, and is scheduled to continue until 6 a.m. Monday, Sept. 21 between Cesar Chavez Street and 17th Street. All northbound lanes will close for the entire weekend. One southbound lane will also close, while three southbound lanes remain open.
That southbound restriction is new. Caltrans' Sept. 9 advisory said all southbound lanes would remain open during the northbound closure. The agency revised the plan Sept. 16 to include the additional lane reduction.
What changed for the Sept. 18–21 Highway 101 closure?
The full northbound shutdown itself has been planned for weeks. The significant change is on the opposite side of the freeway.
Earlier guidance called for all southbound lanes to remain open. Caltrans now says one southbound lane will be closed throughout the weekend, leaving three lanes available to traffic. Drivers heading south should therefore expect reduced capacity even though southbound Highway 101 is not fully closing.
The work is part of the ongoing Fab 4 Hospital Curve Rehabilitation Project. Caltrans says crews will work around the clock during the closure weekend to complete major pavement repairs.
Exactly when does northbound Highway 101 close?
The closure is scheduled to start at 11 p.m. Friday and remain in effect continuously through 6 a.m. Monday.
Northbound traffic will be blocked through the Hospital Curve work area between Cesar Chavez Street and 17th Street. This is not an overnight-only closure: the northbound freeway remains shut Saturday and Sunday.
Caltrans says the work is weather-dependent, so drivers should check current conditions before leaving.
What should drivers use instead?
Caltrans is strongly encouraging northbound drivers to use Interstate 280 for travel toward downtown San Francisco or the Bay Bridge. For southbound travel toward Potrero Hill, SFO, the Peninsula and the South Bay, the agency also points drivers toward I-280 and connections back to southbound U.S. 101.
For airport trips, the official detour maps route traffic between U.S. 101 and I-280 using I-380 on the Peninsula. Anyone traveling to or from SFO should allow substantially more time than normal rather than assuming navigation apps will find an uncongested neighborhood shortcut once traffic builds.
Drivers who do not need a car at their destination may have an easier trip using BART, Caltrain or Muni for the final portion of their journey.
Is southbound Highway 101 still open?
Yes — but at reduced capacity.
Three southbound lanes are scheduled to remain open while one lane closes through the construction zone. That makes the southbound side usable, but not normal. Congestion may build as drivers encounter the work zone and northbound traffic diverts elsewhere.
The distinction matters because the original Caltrans announcement said southbound traffic would remain fully open. That is no longer the current traffic plan.
What does this mean for trips to SFO?
Southbound Highway 101 remains available, but the lane reduction may slow trips from San Francisco toward the airport. Caltrans' detour material also identifies I-280 and I-380 as the alternative route between San Francisco and the U.S. 101/SFO corridor.
For northbound trips from SFO or the Peninsula into San Francisco, the northbound Hospital Curve closure is the larger issue. Caltrans directs drivers to I-380 and I-280 so they can approach the city without relying on the closed northbound section of U.S. 101.
When is the next Hospital Curve closure?
Another major closure is scheduled for Oct. 2–5, but the direction flips. Caltrans plans to close all southbound U.S. 101 lanes between Cesar Chavez Street and 10th Street while keeping northbound lanes open.
A further southbound closure is scheduled for Oct. 16–19. Caltrans says schedules remain subject to weather and construction conditions.