321.258  Arrangement of lights on official traffic-control signals.
  1.  Colored lights placed on a vertical official traffic-control signal face shall be arranged from the top to the bottom in the following order when used:
  a.  Circular red. 
  b.  Steady and/or flashing left-turn red arrow.
  c.  Steady and/or flashing right-turn red arrow.
  d.  Circular yellow.
  e.  Circular green.
  f.  Straight-through green arrow.
  g.  Steady left-turn yellow arrow.
  h.  Flashing left-turn yellow arrow.
  i.  Left-turn green arrow.
  j.  Steady right-turn yellow arrow.
  k.  Flashing right-turn yellow arrow.
  l.  Right-turn green arrow.
  2.  Colored lights placed on a horizontal official traffic-control signal face shall be arranged from the left to the right in the following order when used:
  a.  Circular red.
  b.  Steady and/or flashing left-turn red arrow.
  c.  Steady and/or flashing right-turn red arrow.
  d.  Circular yellow.
  e.  Steady left-turn yellow arrow.
  f.  Flashing left-turn yellow arrow.
  g.  Left-turn green arrow.
  h.  Circular green.
  i.  Straight-through green arrow.
  j.  Steady right-turn yellow arrow.
  k.  Flashing right-turn yellow arrow.
  l.  Right-turn green arrow.
[C79, 81, §321.258]
2014 Acts, ch 1026, §77; 2014 Acts, ch 1123, §17