Ariz. Rev. Stat. § 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:
1. 1. A motor vehicle or vehicle combination with a declared gross weight of more than twenty-six thousand pounds, excluding a motor vehicle designed for carrying sixteen or more passengers, including the driver. For the purposes of this paragraph, "declared gross weight" and "vehicle combination" have the same meaning prescribed in section 28-5431.
2. 2. A vehicle that is drawing a pole trailer that weighs six thousand or more pounds.
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.