SEATTLE – Police are investigating after a motorcycle rider fell off his bike and fell onto street below the West Seattle Bridge. Seattle police say they are investigating what might have caused the rider to fall off his bike. Police say they received calls that the rider had fallen and that a bike was going down the roadway without anyone on it. The motorcycle rider was transported to Harborview Medical Center with critical injuries. Officers investigating single vehicle collision involving a motorcycle on the WSB. Rider fell to Spokane St below. More info when avail. — Seattle Police Dept. (@SeattlePD) September 11, 2016 Seattle police closed S. Spokane Street and East Marginal Way S to investigate as well as the ramp to the West Seattle Bridge from Southbound SR 99. UPDATE: @SeattlePD is now blocking the on ramp to West Seattle Bridge from SB SR 99. Use alt routes. pic.twitter.com/ddBMBZgid9 — seattledot (@seattledot) September 11, 2016 Police have not released cause of the accident or the name of the motorcycle rider.