A man riding his bike eastbound on Noriega Street from Upper Great Highway to Lower Great Highway collided with San Francisco Municipal Railway bus No. 16-X traveling the same direction at about 6:30 p.m. Thursday, police Sgt. Lyn Tomioka said.
The biker, who was allegedly not wearing a helmet, received life-threatening injuries, Tomioka said.
The accident remains under investigation, police said.