Ariz. Rev. Stat. § 28-703 – Alteration of speed limits by local authority

A. If a local authority determines on the basis of an engineering and traffic investigation that the maximum speed permitted under this article is greater or less than is reasonable or safe under the conditions found to exist on any part of a street or highway in its jurisdiction, the local authority may determine and declare a reasonable and safe maximum speed limit at the location and, based on the investigation, may:
1. 1. Decrease the limit at intersections.
2. 2. Increase the limit within any business or residence district to not more than sixty-five miles per hour.
3. 3. Decrease the limit outside any business or residence district.
4. 4. Increase or decrease the limit on streets that are adjacent to or otherwise surrounding school grounds or public parks.
B. A local authority shall determine by an engineering and traffic investigation the proper maximum speed for all arterial streets in its jurisdiction and shall declare a reasonable and safe maximum limit on the arterial streets in its jurisdiction that may be more or less than the maximum speed permitted under this article for a business or residence district.
C. A local authority may decrease the limit to not less than fifteen miles per hour on an unpaved street or road within any district in its jurisdiction if the local authority determines that the limit is necessary to achieve or maintain national ambient air quality standards.
D. An altered limit established as provided for in this section is effective at all times, or during hours of darkness, or at other times as may be determined if appropriate signs giving notice of the altered limit are erected on the street or highway.
E. The alteration of maximum speed limits on state highways or extensions of state highways in a municipality by a local authority is not effective until the director approves the alteration.
F. A local authority shall not make more than six alterations per mile along a street or highway pursuant to this section, except for reduced limits at intersections. The difference between adjacent limits shall not be more than ten miles per hour except for school crossings.