S.F. could get its first freeway carpool lane
An oft-gridlocked, mile-long segment of northbound Interstate 280 may become the site of San Francisco’s first freeway carpool lane.
Severe congestion has long plagued commutes on the northbound I-280 segment from 18th Street to the King Street offramp that takes motorists to Oracle Park and the Embarcadero.
That traffic congestion has mostly returned to pre-pandemic standards, and transportation officials are looking into options that could add a lane for Muni and SamTrans express buses and high-occupancy vehicles carrying three or more people.
One option would be to restripe the existing left shoulder to turn northbound I-280 between 18th Street and the King Street off-ramp from four lanes to five, with the leftmost lane reserved for carpools and transit. I-280’s King Street off-ramp, through the Fifth Street intersection, would become three lanes with an added lane.
Another alternative that transportation officials at the San Francisco County Transportation Authority are studying includes converting the freeway’s left lane into a carpool lane. This would reduce general traffic to two lanes before the King Street off-ramp, and a single lane on the off-ramp.
“The purpose of the project is to give priority to high-occupancy modes, like transit and three person-plus carpools,” said Rachel Hiatt, the transportation authority’s deputy director for planning. “Those sorts of more efficient modes do not have priority on our freeway network today the way they do have priority on parts of our surface street network. That’s one of the main reasons that we started looking into this type of treatment.”
Transportation officials are gathering public feedback before they settle on a recommendation, which requires the approval of Caltrans and the city’s Board of Supervisors. Construction could begin in 2026.
Some residents have spoken out against widening Interstate 280 because of fears that it would add more traffic to the busy Fourth and King intersection. The intersection is part of San Francisco’s “high-injury network” and was the site of the tragic death of a 4-year-old girl who was struck by a motorist who failed to yield to crossing pedestrians.
“Adding highway capacity and adding lanes is not the right move for safety,” said Robin Pam, founder of the KidSafe SF street safety advocacy group. “It’s not the right move for the climate, and it really is not the right move for San Francisco.”
Public feedback, so far, has centered on concerns over whether the carpool lane would add more traffic rather than reduce it, as well as calls to prioritize pedestrian safety on surface streets.
“We agree with that feedback and share those concerns,” Hiatt said, regarding pedestrian safety.
Many other aspects of the project remain unanswered.
Transportation officials, for instance, are weighing how far to extend the carpool lane after I-280 turns into King Street at the Fifth Street intersection. An extension to Third Street would connect the carpool lane to an existing transit-only lane.
Also unclear are the hours of enforcement, which are likely to encompass peak morning and afternoon commute times, and whether the project would include tolling like the Bay Area’s broader network of express lanes.
A 2018 study by the County Transportation Authority recommended “HOV3+” lanes in which vehicles with three or more people can use the lane for free with a “demand-based, variable toll” for other cars. Carpool lanes without a toll or lower minimum occupancy requirement either were expected to make little difference to traffic congestion or worsen it, according to the study.
Transportation officials are also considering adding a continuous southbound carpool lane on I-280 and Highway 101 that would extend to the San Mateo County border. That effort, though, is further down the road than the northbound carpool lane, which city supervisors decided to prioritize in 2020.
Another effort with dimmer prospects is extending the northbound carpool lane to connect it to Highway 101 in San Mateo County, which would require constructing a new flyover ramp at the I-280 interchange.
Still, the region’s transportation officials’ long-term plans call for building continuous HOV or express lanes, at least in the southbound direction, from San Francisco to San Jose.
A 22-mile extension of express lanes on Highway 101 to Interstate 380 opened for toll service last spring, and a contentious debate is underway in San Mateo County over whether to further extend it to the San Francisco border.
Like San Francisco, San Mateo officials are weighing a thorny question — whether to convert an existing lane or carve a new lane from the existing shoulder.
“Highway widening doesn’t reduce congestion, it simply encourages more people to drive instead of taking Caltrain or BART,” said Mike Swire, a member of the San Mateo transportation authority’s citizens’ advisory committee.