A woman in her 80s was taken to hospital last night.
A van and a pedestrian were involved in a collision near the junction with Osberton Road last night.
Emergency crews were called to the scene shortly before 8pm and the pedestrian was taken to hospital with serious injuries.
She remains there this evening in a life-threatening condition, according to Police.
A 45-year-old man from Thatcham was arrested on suspicion of driving a motor vehicle whilst unfit through drink and drugs and causing serious injury by dangerous driving.
He has been released under investigation.
PC Julia Stroud from the Serious Collision Investigation Unit at Bicester said: “We are appealing for any witnesses to this incident to please come forward.
“We’d also ask anyone with dash-cams and who was in the area around the time of this incident to please check any footage in case it may have captured something that could assist with our investigation."
Anyone with information should call 101 quoting reference 43220347166.