321.306  Roadways laned for traffic.
  Whenever any roadway has been divided into three or more clearly marked lanes for traffic the following rules in addition to all others consistent herewith shall apply:
  1.  A vehicle shall be driven as nearly as practical entirely within a single lane and shall not be moved from such lane until the driver has first ascertained that such movement can be made with safety.
  2.  If a roadway is divided into three lanes, a vehicle shall not be driven in the center lane except as follows: 
  a.  When overtaking and passing another vehicle where the roadway is clearly visible and such center lane is clear of traffic within a safe distance. 
  b.  In preparation for a left turn or where such center lane is at the time allocated exclusively to traffic moving in the direction the vehicle is proceeding and is signposted to give notice of such allocation.
  3.  Official signs may be erected directing slow-moving traffic to use a designated lane or allocating specified lanes to traffic moving in the same direction and drivers of vehicles shall obey the directions of every such sign.
  4.  Vehicles moving in a lane designated for slow-moving traffic shall yield the right-of-way to vehicles moving in the same direction in a lane not so designated when such lanes merge to form a single lane.
  5.  A portion of a highway provided with a lane for slow-moving vehicles does not become a roadway marked for three lanes of traffic.
[C39, §5024.10; C46, 50, 54, 58, 62, 66, 71, 73, 75, 77, 79, 81, §321.306]
2010 Acts, ch 1069, §94
Referred to in §321.208, 321.482A, 805.8A(6)(k)
For applicable scheduled fine, see §805.8A, subsection 6
Additional penalties for violations causing serious injury or death, see §321.482A