Utah Code § 41-6a-1703: Prohibition as to passenger riding on improper portion of motor vehicle -- Exceptions.

(1) A person may not ride and a person operating a motor vehicle may not knowingly permit a person to ride on any portion of a vehicle not designed or intended for the use of passengers.

(2) This provision does not apply to:

(a) a vehicle that is not being operated on a highway;

(b) an employee engaged in the necessary discharge of the employee's duty; or

(c) a person riding within or on a motor vehicle in a space intended for a load on the vehicle.