Wisconsin Statutes Vehicles (Ch. 340 to 351) § 346.13. Driving on roadways laned for traffic

(1) Except as provided in sub. (4), the operator of a vehicle shall drive as nearly as practicable entirely within a single lane and shall not deviate from the traffic lane in which the operator is driving without first ascertaining that such movement can be made with safety to other vehicles approaching from the rear.

(2) Except as provided in s. 346.05(1)(g), upon a 2-way roadway which is divided into 3 lanes the operator of a vehicle may not drive in the center lane except when overtaking and passing another vehicle where the roadway is clearly visible and the center lane is clear of traffic within a safe distance, or in preparation for a left turn or U-turn, or where the center lane is at the time allocated exclusively to traffic moving in the direction the vehicle is proceeding and is marked or posted to give notice of the allocation.

(3) Notwithstanding sub. (2), but subject to sub. (4), when lanes have been marked or posted for traffic moving in a particular direction or at designated speeds, the operator of a vehicle shall drive in the lane designated.

(4) Upon a 2-way roadway with at least 2 lanes for travel in each direction, a wide implement of husbandry, as defined in s. 347.24(3)(a), that is being operated in compliance with any applicable requirement under s. 347.24(3), 347.245(1), or 347.25(2g), and that is being operated as much as practicable within a single lane may, to the extent necessary, extend into another lane intended for travel in the same direction if it does not impede other vehicles approaching from the rear.

(5) Notwithstanding sub. (1), the operator of a vehicle or combination of vehicles with a total length of not less than 40 feet or a total width of not less than 10 feet may, with due regard for all other traffic, deviate from the lane in which the operator is driving to the extent necessary to approach and drive through a roundabout.