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 constructed to substantially impede crossing by vehicular traffic, the operator of a vehicle shall drive only to the right of the space or barrier and no operator of a vehicle shall drive over, across, or within the 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 or making a U-turn may drive across a paved dividing space or a physical barrier not constructed to impede crossing by vehicular traffic, unless the crossing is prohibited by signs erected by the authority in charge of the maintenance of the highway.
Wis. Stat. § 346.15