TUCSON, Ariz. — Police say an Arizona school bus driver passed out behind the wheel, causing the vehicle to careen onto a sidewalk where it struck and killed a woman riding a scooter.

Officers say the wreck in Tucson Wednesday afternoon remains under investigation but that there’s no indication that speed or drug or alcohol impairment was a factor. Police said no citations have been issued.

Sgt. Kimberly Bay says the bus veered onto the adjacent sidewalk and struck several trees and poles before hitting the woman.

She was pronounced dead at the scene.

Bay says the bus driver and one teenage student aboard the bus weren’t injured.

No identities were released.