(a) A directional sign may not contain, include, or be illuminated by flashing, intermittent, or moving lights.
(b) Lights that are a part of or illuminate a directional sign:
  (1) must be shielded so that beams or rays of light are not being directed at any portion of the traveled way of an interstate or primary highway; and
  (2) may not be of such intensity or brilliance that they:
    (A) impair the vision of the driver of a motor vehicle on an interstate or primary highway or otherwise interfere with the driver's operation of the motor vehicle; or
    (B) obscure or interfere with the effectiveness of an official traffic sign, device, or signal.

Source Note: The provisions of this §21.947 adopted to be effective July 1, 2011, 36 TexReg 2418