Whenever any highway has been divided into two or more roadways by leaving an intervening space or by a physical barrier or clearly indicated dividing section or by a median island not less than eighteen inches wide formed either by solid yellow pavement markings or by a yellow crosshatching between two solid yellow lines so installed as to control vehicular traffic, every vehicle shall be driven only upon the right-hand roadway unless directed or permitted to use another roadway by official traffic-control devices or police officers. No vehicle shall be driven over, across or within any such dividing space, barrier or section, or median island, except through an opening in such physical barrier or dividing section or space or median island, or at a crossover or intersection established by public authority.