Utah Code § 41-6a-605: Minimum speed regulations.

(1) A person may not operate a motor vehicle at a speed so slow as to impede or block the normal and reasonable movement of traffic except when:

(a) a reduced speed is necessary for safe operation;

(b) upon a grade; or

(c) in compliance with a traffic-control device.

(2) Operating a motor vehicle on a limited access highway at less than the speed limit side by side with and at the same speed as a vehicle operated in the adjacent right lane is evidence of a violation of Subsection (1).

(3)

(a) If, based on an engineering and traffic investigation, a highway authority determines that slow speeds on any part of a highway under its jurisdiction consistently impede the normal and reasonable movement of traffic, the highway authority may post a minimum speed limit.

(b) If a minimum speed limit is posted under this Subsection (3), a person may not operate a vehicle at a speed below the posted minimum speed limit except:

(i) when necessary for safe operation; or

(ii) in accordance with Section 41-6a-205.

(c) The minimum speed limit is effective when appropriate signs giving notice are erected along the highway or section of the highway.

(4) A violation of this section is an infraction.