Tex. Transp. Code § 623.0181

The department may issue a permit that authorizes the operation of a commercial motor vehicle, trailer, semitrailer, or combination of those vehicles, or a truck-tractor or combination of a truck-tractor and one or more other vehicles, that exceeds the maximum weight limit as set by the department due to the presence of an auxiliary power unit that allows the vehicle to operate on electricity or battery power if the department finds that such an exemption would reduce nitrogen oxide emissions.