(1)    Upon any roadway where traffic is permitted to move in both directions simultaneously, the operator of a vehicle shall not drive to the left side of the center of the roadway in overtaking and passing another vehicle proceeding in the same direction unless such left side is clearly visible and is free of oncoming traffic for a sufficient distance ahead to permit such overtaking and passing to be done in safety. In no case when overtaking and passing on a roadway divided into 4 or more clearly indicated lanes shall the operator of a vehicle drive to the left of the pavement marking indicating allocation of lanes to vehicles moving in the opposite direction or, in the absence of such pavement marking, to the left of the center of the roadway. Except as provided in sub. (3) (b) and s. 346.05 (1) (g), in no case shall the operator of a vehicle drive in a lane when signs or signals indicate that such lane is allocated exclusively to vehicles moving in the opposite direction.

   (2)   Upon any roadway where traffic is permitted to move in both directions simultaneously, the operator of a vehicle shall not drive on the left side of the center of the roadway upon any part of a grade or upon a curve in the roadway where the operator’s view is obstructed for such a distance as to create a hazard in the event another vehicle might approach from the opposite direction.

   (3)   

      (a)    Except as provided in par. (b), the operator of a vehicle shall not drive on the left side of the center of a roadway on any portion thereof which has been designated a no-passing zone, either by signs or by a yellow unbroken line on the pavement on the right-hand side of and adjacent to the center line of the roadway, provided such signs or lines would be clearly visible to an ordinarily observant person.

      (b)    The operator of a vehicle may drive on the left side of the center of a roadway on any portion thereof which has been designated a no-passing zone, as described in par. (a), to overtake and pass, with care, any vehicle, except an implement of husbandry or agricultural commercial motor vehicle, traveling at a speed less than half of the applicable speed limit at the place of passing.

   (4)   Other provisions of this section notwithstanding, the operator of a vehicle may not overtake and pass on the left any other vehicle which, by means of signals as required by s. 346.34 (1), indicates its intention to make a left turn or U-turn.