The motorcyclist, 47, of Alamo, was driving in commute traffic in the second lane from the left. She looked over her left shoulder to prepare to change lanes and when she looked back the traffic in her lane was stopped, said CHP Officer Tom Maguire.
She wasn't able to stop in time and rear-ended the Honda Accord in front of her, he said. Police do not know how fast she was going at the time.
"She was ejected off the motorcycle," said Maguire. "She's OK. She doesn't have any life threatening injuries."
She was transported to John Muir Medical Center in Walnut Creek as a precaution. The driver of the Honda was not injured.
Both left lanes were shut down for about 15 minutes due to the accident, said Maguire. Traffic on the freeway was backed up about two miles to Rudgear Road in Walnut Creek.