Arizona Revised Statutes Title 28. Transportation § 28-702. State highway speed limits

A. If the director determines on the basis of an engineering and traffic investigation that any maximum speed limit is greater or less than is reasonable or safe under the conditions found to exist on any part of a state highway, the director may determine and declare a reasonable and safe maximum speed limit or varying speed limits for the location.

B. The maximum speed limit determined pursuant to this section is effective when appropriate signs giving notice of the maximum speed limit are erected.

C. The director may declare a maximum speed limit that is determined pursuant to this section to be effective at all times or at such times as indicated on the speed limit signs.  The director may establish varying speed limits for different times of day, different types of vehicles, varying weather conditions and other factors bearing on safe speeds.  The varying limits are effective when posted on appropriate fixed or variable signs.