A.R.S. § 28-858: Approaching horses and livestock

A person operating a motor vehicle on a public highway and approaching a horse-drawn vehicle, a horse on which a person is riding or livestock being driven on the highway shall exercise reasonable precaution to prevent frightening and to safeguard the animals and to ensure the safety of persons riding or driving the animals. If the animals appear frightened, the person in control of the vehicle shall reduce its speed and if requested by signal or otherwise shall not proceed further toward the animals unless necessary to avoid accident or injury until the animals appear to be under control.