A UCSF shuttle bus stopped at a red light near San Francisco General Hospital was rear-ended this morning in a chain-reaction traffic collision, said the San Francisco Police Department. Approximately six people were taken to local hospitals with non-life-threatening injuries, police said. Altogether, four vehicles were involved in the accident, police reported. Sgt. Michael Andraychak said the accident began shortly before 11:30 a.m. when a white four-door vehicle travelling southbound on Potrero Avenue crashed into a blue Nissan sedan – the sedan in turn rear-ended the shuttle bus stopped at the intersection of Potrero and 22nd Street. Also damaged was a white pickup parked nearby. “The UCSF driver was stopped at a light and was rear-ended,’’ Andraychak said. No arrests were made, he said. The shuttle bus was on its regular route between the 16th Street BART station, the Mission Center and San Francisco General Hospital, said Jon Gledhill, director of UCSF Transportation Services. The shuttle buses ferry employees and patients throughout the UCSF campus network in San Francisco, covering 16 routes. The vans travel one million miles a year and carry 2.3 million passengers annually.