Ariz. Rev. Stat. § 28-706 – Special speed limitations

A. A person shall not drive a vehicle equipped with solid rubber or cushion tires at a speed of more than ten miles per hour.
B. A person shall not drive a vehicle over any bridge or other elevated structure constituting a part of a highway at a speed that is greater than the maximum speed that can be maintained with safety to the bridge or structure if the structure is signposted as provided in this section.
C. On request from any local authority or on the director's own initiative, the director may conduct an investigation of any bridge or other elevated structure constituting a part of a highway. If the director finds that the structure cannot safely withstand vehicles traveling at the speed otherwise permissible under this article, the director shall:
1. 1. Determine and declare the maximum speed of vehicles that the structure can withstand.
2. 2. Cause or permit suitable signs stating the maximum speed to be erected and maintained at a distance of three hundred feet before each end of the structure.
D. At the trial of a person charged with a violation of this section, proof of a determination of the maximum speed by the director and the existence of the signs are conclusive evidence of the maximum speed that can be maintained with safety to the bridge or structure.