61-8-310. When local authorities may and shall alter limits or establish or alter area of school zone. (1) If a local authority in its jurisdiction determines on the basis of an engineering and traffic investigation that the speed permitted under 61-8-303 and 61-8-309 through 61-8-313 is greater or less than is reasonable and safe under the conditions found to exist upon a highway or part of a highway, the local authority may set a reasonable and safe limit that:

(a) decreases the limit at an intersection;

(b) increases the limit within an urban district, but not to more than 65 miles an hour during the nighttime;

(c) decreases the limit outside an urban district, but not to less than 35 miles an hour on a paved road or less than 25 miles an hour on an unpaved road; or

(d) decreases the limit in a school zone or in an area near a senior citizen center, as defined in 23-5-112, or a designated crosswalk that is close to a school or a senior citizen center to not less than 15 miles an hour. If warranted by an engineering and traffic investigation, a local authority may adopt variable speed limits to adapt to traffic conditions by time of day, provided that the variable limits comply with the provisions of 61-8-206.

(2) A board of county commissioners may set limits, as provided in subsections (1)(c) and (1)(d), without an engineering and traffic investigation on a county road.

(3) A local authority in its jurisdiction may determine the proper speed for all arterial streets and shall set a reasonable and safe limit on arterial streets that may be greater or less than the speed permitted under 61-8-303 for an urban district.

(4) (a) An altered limit established as authorized under this section is effective at all times or at other times determined by the authority when appropriate signs giving notice of the altered limit are erected upon the highway.

(b) If a local authority decreases a speed limit in a school zone, the local authority shall erect signs conforming with the manual adopted by the department of transportation under 61-8-202 giving notice that the school zone has been entered, of the altered speed limit and the penalty provided in 61-8-726, and that the school zone has ended.

(5) The commission has exclusive jurisdiction to set special speed limits on all state highways or highways located on the commission-designated highway system as defined in 60-1-103 in all municipalities or urban areas. The commission shall set these limits in accordance with 61-8-309.

(6) A local authority establishing or altering the area of a school zone shall consult with the department of transportation and the commission if the school zone includes a state highway or a highway located on the commission-designated highway system as defined in 60-1-103.

(7) A local authority shall consult with district officials for a school when:

(a) establishing or altering the area of a school zone near the school; or

(b) setting a speed limit pursuant to subsection (1)(d) in a school zone near the school.

(8) A speed limit set on an unpaved road under subsection (1)(c) must be the same for all types of motor vehicles that may be operated on the road.

(9) The violation of a speed limit established under subsections (1)(a) through (1)(c) is a misdemeanor offense and is punishable as provided in 61-8-711. The violation of a speed limit established under subsection (1)(d) is a misdemeanor offense and is punishable as provided in 61-8-726.