331.01  DRIVING UPON RIGHT SIDE OF ROADWAY; EXCEPTIONS.
   (a)   Upon all roadways of sufficient width, a vehicle shall be driven upon the right half of the roadway, except as follows:
      (1)   When overtaking and passing another vehicle proceeding in the same direction, or when making a left turn under the rules governing such movements;
      (2)   When an obstruction exists making it necessary to drive to the left of the center of the highway; provided, any person so doing shall yield the right-of-way to all vehicles traveling in the proper direction upon the unobstructed portion of the highway within such distance as to constitute an immediate hazard;
      (3)   When driving upon a roadway divided into three or more marked lanes for traffic under the rules applicable thereon;
      (4)   When driving upon a roadway designated and posted with signs for one-way traffic;
      (5)   When otherwise directed by a police officer or traffic-control device.
   (b)   Upon all roadways, any vehicle proceeding at less than the normal speed of traffic at the time and place and under the conditions then existing shall be driven in the right-hand lane then available for traffic, or as close as practicable to the right-hand curb or edge of the roadway, except when overtaking and passing another vehicle proceeding in the same direction or when preparing for a left turn.
   (c)   Upon any roadway having four or more lanes for moving traffic and providing for two-way movement of traffic, no vehicle shall be driven to the left of the center line of the roadway, except when authorized by official traffic-control devices designating certain lanes to the left of the center of the roadway for use by traffic not otherwise permitted to use the lanes, or except as permitted under division (a)(2) of this section.  This section shall not be construed as prohibiting the crossing of the center line in making a left turn into or from an alley, private road, or driveway.
(ORC 4511.25)
Penalty - see Sections 307.01 and 307.02