Section 1116. Lane direction control indications

Whenever  traffic  is
  controlled by lane direction control signals located over the individual
  lanes of a highway, only the colors green, yellow and red shall be used,
  and said signals shall indicate and apply as follows:
    (a) Traffic facing a steady downward pointing green arrow  signal  may
  travel in any lane over which such signal is located.
    (b) Traffic facing a steady yellow X signal is thereby warned that the
  related  green  downward arrow indication is being terminated and that a
  red X indication will  be  exhibited  immediately  thereafter  and  such
  traffic  shall vacate, in a safe manner, the lane over which such signal
  is located.
    (c) Traffic facing a flashing yellow X signal may travel in  any  lane
  over which such signal is shown preparatory to making a left turn, using
  proper caution.
    (d)  Traffic facing a steady red X signal shall not enter or travel in
  any lane over which such signal is located.