Driver's at fault... at least in Colorado.
Back in my days of my youth (I was, 12?), I was riding in Glenwood Springs, CO. Was riding on the sidewalk, downhill, going fairly fast. Driver in a truck pulls out of a parking lot, completely not looking for me. I smacked right into the side of his truck. Left a nice large dent and face print in the side of the truck. Broke my collar bone.
Anyways, driver left the scene. My brother got the license plate. Police found him. Cited him for leaving the scene and something else. Police found him at fault for the accident.
My family could have sued for medical expenses. Chose not to.
IOW, driver would be at fault in Colorado.