21651. (a) Whenever a highway has been divided into two or more
roadways by means of intermittent barriers or by means of a dividing
section of not less than two feet in width, either unpaved or
delineated by curbs, double-parallel lines, or other markings on the
roadway, it is unlawful to do either of the following:
(1) To drive any vehicle over, upon, or across the dividing
section.
(2) To make any left, semicircular, or U-turn with the vehicle on
the divided highway, except through an opening in the barrier
designated and intended by public authorities for the use of vehicles
or through a plainly marked opening in the dividing section.