Tex. Transp. Code § 547.507

Unless sufficient light exists to reveal a person or vehicle at a distance of 1,000 feet, the operator of a vehicle described by Section 547.503(b) or an explosive cargo vehicle that is disabled, or stopped for more than 10 minutes, within 500 feet of a curve, hillcrest, or other obstruction to view shall place the required warning device for the direction of the obstruction from 100 to 500 feet from the vehicle so as to provide ample warning to other traffic.