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:  Circular red, circular yellow, circular green, straight through yellow arrow, straight through green arrow, left turn yellow arrow, left turn green arrow, right turn yellow arrow, and 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:  Circular red, circular yellow, left turn yellow arrow, left turn green arrow, circular green, straight through yellow arrow, straight through green arrow, right turn yellow arrow, and right turn green arrow.
[C79, 81, §321.258]