Annual emissions inspections must be passed prior to registration and registration renewal in the counties of Brazoria, Collin, Dallas, Denton, El Paso, Ellis, Fort Bend, Galveston, Harris, Johnson, Kaufman, Montgomery, Parker, Rockwall, Tarrant, Travis, and Williamson.
Diesel Vehicles:
Diesel vehicles are not tested for emissions.
Exemptions:
1. New vehicles for the newest two (2) model years
2. Vehicles with "Antique" registration and plates
3. Vehicles 25 years old or older
4. Vehicles registered as "Classic" are only required to have a safety inspection
5. Kit Cars are required to meet the emissions standards for the year the vehicle is assembled.
For more information visit: https://www.dps.texas.gov
Texas Code
§ 547.604. Muffler Required
(a) A motor vehicle shall be equipped with a muffler in good working condition that continually operates to prevent excessive or unusual noise.
(b) A person may not use a muffler cutout, bypass, or similar device on a motor vehicle.

Antique
Available for vehicles that are at least 25 years old, a collector's item, and not used exclusively for exhibitions, club activities, parades, and other functions of public interest and is not used for regular transportation. Only a single rear plate is required. The license plate must include the words “Antique Auto,” “Antique Truck,” “Antique Motorcycle,” “Antique Bus,” or “Military Vehicle,” as appropriate.

Classic
Available for vehicles that are at least 25 years old.

Custom
Available for vehicles with a model year after 1948 that are at least 25 years old, and replicas of such vehicles, that have been altered from the manufacturer's original design or have a body constructed from non-original materials.

Street Rod
Available for vehicles manufactured before 1949, and replicas of such vehicles, that have been altered from the manufacturer's original design or have a body constructed from non-original materials.

YOM
Vehicles registered as "Antique," "Classic," "Custom" or "Street Rod" may display YOM plates with DMV approval.