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 so constructed as to impede vehicular traffic, every vehicle must 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 may be driven over, across, or within any such dividing space, barrier, or section, except through an opening in such physical barrier or dividing section or space or at a crossover or intersection as established by public authority, unless such crossing is specifically prohibited and such prohibition is indicated by appropriate traffic-control devices.