The protesters walked up an off-ramp from Fourth Street and blocked cars heading toward the bay bridge, bringing the evening commute to a sudden stop.
A couple of drivers got out of their cars and confronted the protesters. There was some pushing and shoving, but the conflict did not escalate.
The California Highway Patrol arrived and the road was cleared fairly quickly. Officers detained six people here. Authorities tell KTVU all six were taken to the city jail and booked for unlawful assembly and being a public nuisance.
Another group of protesters was reported to be blocking traffic on Market Street near 5th Street in San Francisco at about 4:40 p.m. That coupled with reported Muni issues made for slow evening commute in downtown SF.
The protesters eventually moved on, marching back to the Mission District down Valencia Street to 24th and eventually returning to the BART Station at 24th and Mission. The crowd eventually dispersed.
Hours earlier, a group of about 200 protesters gathered at the corner of 24th and Mission Street in San Francisco and marched up Van Ness to City Hall.
A line of seven law enforcement officers met the demonstrators on the front stairs of city hall, but were quickly overwhelmed as protesters surged into the building and filled the rotunda.
The demonstrators chanted and waved posters bearing the images of victims of police killings from across the country. A second line of police officers stood nearby ready to move in at any sign of vandalism.
The action came a few hours after another City Hall protest had broken up peacefully after a noon rally.
San Francisco Supervisors John Avalos and David Campos and other community leaders had taken part in that rally as protesters chanted "Mayor Lee can't you see, inequality is killing me" and held signs that read "Black And Brown Lives Matter."
Many protesters said they were disappointed with how the city has handled racist and homophobic text messages sent between San Francisco police officers.
They maintained that officers under investigation for involvement in such activities should be placed on unpaid, not paid, administrative leave and supported independent investigations into the matter.
Avalos aired his frustration with what he said is growing inequality and racial profiling in America and what he called "the lip service" paid to the cause.
He said the city is dealing with racial profiling and racial discrimination.
Avalos said that black individuals in the Bayview District are under constant surveillance and racially profiled, but said if you're white and "If you're out there partying in Dolores Park, nothing happens."
Supervisor Campos said the city has the fastest growing inequality of any city in the country and that if San Francisco were a country, it "would be up there with Rwanda," in terms of inequality.
"We have had enough," Campos said.
Amos Brown, San Francisco branch president of the National Association for the Advancement of Colored People, was in the crowd and said, "I know that business as usual has been interrupted, but there comes a time when we the oppressed must rise up."
The protests were among several planned in the Bay Area.
In San Jose, protesters rallied at San Jose State then marched to City Hall.
One woman whose partner was killed by San Jose State police said she wants police to be held accountable.
She applauded the good cops, but said she wants the bad cops punished. Others called for more police oversight.
At UC Berkeley, the demonstration was more low-key.
Organizers handed out leaflets demanding justice for minorities who have been killed by police.
They said that the judicial system is biased against minorities, but one student spoke out for police, saying they have a tough job.