Angelica Marie Portillo was allegedly driving under the influence of alcohol when she turned into the patrol car, which had its lights flashing and siren blaring, according to police.
At about 6 p.m., a Santa Rosa police officer was driving northbound on Mendocino Avenue in response to an emergency that was occurring at Steele Lane.
The patrol car reached some backed-up traffic near Ross Street and pulled into the southbound lane to pass the congested vehicles.
As the officer traveled north in the southbound lane, Portillo turned north from Ross Street onto Mendocino Avenue and hit the patrol car.
No one was injured in the collision.
Officers determined Portillo's blood alcohol level was more than twice the legal limit, according to police.
She was arrested on drunken driving charges and booked in the Sonoma County jail.