Boulder police Sgt. Jim MacPherson said witnesses said the motorcyclist was traveling at a high rate of speed and weaving in and out of traffic around 7:30 p.m. She apparently lost control, slid and hit the back of another car.
MacPherson said her injuries are serious and considered life-threatening. He did not release the name or age of the woman.
No one else was injured, MacPherson said.
Broadway was closed at Pleasant Avenue to southbound traffic as Boulder police investigated the accident. It reopened around 8:20 p.m.