Wis. Stat. § 346.15

Whenever any highway has been divided into 2 roadways by an intervening unpaved or otherwise clearly indicated dividing space or by a physical barrier so constructed as to substantially impede crossing by vehicular traffic, the operator of a vehicle shall drive only to the right of such space or barrier and no operator of a vehicle shall drive over, across or within any such space or barrier except through an opening or at a crossover or intersection established by the authority in charge of the maintenance of the highway, except that the operator of a vehicle when making a left turn to or from a private driveway, alley or highway may drive across a paved dividing space or a physical barrier not so constructed as to impede crossing by vehicular traffic, unless such crossing is prohibited by signs erected by the authority in charge of the maintenance of the highway.