Nancy Ho, of San Francisco, was traveling east on Mission Street when she was struck by a westbound Berkeley Farms truck as she turned left onto Fremont street around 8 a.m., San Francisco police Lt. Troy Dangerfield said.
Ho was taken to San Francisco General Hospital to be treated for a serious head wound and other injuries, he said. She was not wearing a helmet.
Although both Ho and the truck driver had a green light, she was making an illegal left turn, Dangerfield said.
Left turns are only permitted for taxis and San Francisco Municipal Transportation Agency buses, according to posted signs.
A video camera at a nearby business captured the collision, and police are reviewing the footage, he said.
Dangerfield said that bicyclists, motorists and pedestrians should be alert when navigating San Francisco streets.
"Everyone has to share the roadway and be cautious," he said.
Investigators do not suspect that drugs or alcohol played a role in the collision. The driver of the truck, owned by the Newark-based company Sunrise Food Distributors Inc., was cooperative with detectives.
San Francisco police did not provide any updates about the investigation this morning. The intersection was closed for a couple of hours while investigators gathered evidence.