(a) A person commits an offense if in any park or recreational area he knowingly:
(1) Drives a motor vehicle;
(2) Stops, stands, or parks a motor vehicle;
(3) Parks a motor vehicle so as to obstruct entrance to or exit from a roadway, parking area, or trail established for public motor vehicle use; or
(4) Fails to park the entire motor vehicle within the limit lines of a designated parking stall, where such lines have been provided.
(b) It is a defense to prosecution under subsection (a) that the driving, stopping, standing, or parking:
(1) Was along a roadway, trail, or parking area established for public motor vehicle use;
(2) Was due to temporary mechanical failure of the vehicle;
(3) Was ordered by a police or park officer or a person charged with supervision of a park or recreation area within the city; or
(4) Was performed by an employee of the city while in the course of his official duties.