A.R.S. § 28-727: No passing zones

The director may determine those portions of a highway where overtaking and passing or driving to the left of the roadway would be especially hazardous and may indicate the beginning and end of the zones by appropriate signs or markings on the roadway. When the signs or markings are in place and clearly visible to an ordinarily observant person, every driver of a vehicle shall obey the directions of the signs or markings.