Tex. Transportation Code § 451.415: EXEMPTIONS.

(a) The following vehicles are exempt from a vehicle emissions tax imposed by an authority on the owner of the vehicle:

(1) a vehicle that is the property of and used exclusively in the service of the United States, this state, or a county, municipality, school district, or authority of this state;

(2) a vehicle used exclusively for fire fighting; and

(3) a vehicle that:

(A) is owned by a person doing business both in and outside the authority or only outside the authority;

(B) is not stationed or customarily kept in the authority; and

(C) is operated in the authority for an average period of less than two days each calendar week during a tax year or portion of a tax year during which the tax accrues.

(b) To receive the exemption under Subsection (a)(3), the owner of a vehicle must file with the county assessor-collector an affidavit specifying each vehicle for which the exemption is claimed.

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