The 43-year-old from the York area is being treated in hospital after officers breathalysed her on Main Avenue, York, at around 2.10pm.
A North Yorkshire Police spokesman said: “A member of the public reported concerns for the safety of a 43-year-old woman found in a Vauxhall Zafira.
“The vehicle was parked at the side of the road on Main Avenue.
“Officers attended the scene and breathalysed the woman, who provided a positive breath test.
“She was arrested on suspicion of being in charge of a vehicle while being unfit through drink.”
The spokesman added that the woman has been taken to York District Hospital for treatment but her condition is unknown.