The 62-year-old man was driving a blue SUV that struck the San Francisco Municipal Railway cable car at Geary and Powell streets at about 10 p.m., according to police.
Bystanders detained the man until officers arrived and arrested him on suspicion of DUI, police said. His name had not been released as of this morning.
The cable car operator, a 43-year-old man, was taken to a hospital after complaining of pain to his shoulder, police spokesman Officer Albie Esparza said.
Muni spokesman Paul Rose said there were about 15 passengers on the cable car but that the employee was the only one injured.
Rose said the cable car line was reopened later that night.