Arizona Revised Statutes Title 28. Transportation § 28-709. Maximum speed limit for large vehicles and vehicles with trailers

A. Unless a lower maximum speed limit is posted or the department designates a greater maximum speed limit pursuant to subsection B of this section, a person shall not drive either of the following on a highway in this state at a speed that is greater than sixty-five miles per hour:  

B. If the department determines on the basis of an engineering and traffic investigation of a highway under its jurisdiction that the designation of a maximum speed limit for vehicles prescribed in subsection A of this section that is greater than sixty-five miles per hour would facilitate the safe and orderly movement of traffic, the department may designate such a maximum speed for travel of those vehicles and shall erect signs at reasonable intervals giving notice of the speed limitation.