Tex. Transportation Code § 547.503: DISPLAY OF HAZARD LAMPS.

(a) The operator of a vehicle that is described by Subsection (b) and that is stopped on a roadway or shoulder shall immediately display vehicular hazard warning lamps that comply with Section 547.331, unless the vehicle:

(1) is parked lawfully in an urban district;

(2) is stopped lawfully to receive or discharge a passenger;

(3) is stopped to avoid conflict with other traffic;

(4) is stopped to comply with a direction of a police officer or an official traffic-control device; or

(5) displays other warning devices as required by Sections 547.504-547.507.

(b) This section applies to a truck, bus, truck-tractor, trailer, semitrailer, or pole trailer at least 80 inches wide or at least 30 feet long.

Acts 1995, 74th Leg., ch. 165, Sec. 1, eff. Sept. 1, 1995.