Smog Laws by State

Most states require motorists to have their vehicle's emission levels tested to ensure air pollution levels stay below a predetermined level. These statutes, or "smog laws," are in place to protect public health and the environment by reducing pollutants that contribute to smog.

In states with such requirements, you must submit proof that your vehicle meets emissions standards as part of your vehicle registration renewal process.

State Requirements and Standards for Testing

Every state has its process and standards for an acceptable pollution level from a vehicle. Sometimes, these regulations only apply to dense urban areas. For example, Missouri's emissions standards and inspection requirements apply only to the St. Louis Metropolitan Area.

Certain vehicles are usually exempt from emissions testing requirements. Although this can vary by state, some of these exemptions include:

• Antique vehicles that have classic automobile registration or official vintage license plates
• Newer vehicles (typically less than three model years old), as manufacturers are now required to meet specific environmental standards
• Motorcycles
• RVs and motor homes
• Some heavy-duty, diesel-powered vehicles
• Electric vehicles and alternative fuel vehicles

Emissions standards vary by state and can change over time. Some areas have more stringent rules to encourage the use and development of more fuel-efficient vehicles. You may face strict, lenient, or no requirements depending on your area.

Vehicle Emissions: Statistics

The U.S. Environmental Protection Agency (EPA) reports that 29% of all greenhouse gas emissions are from transportation. This makes vehicle emissions the second-highest pollution emitter by industry, following only electricity generation. Cars have gotten much more efficient and clean burning, but the increasing number of vehicles on the road has kept emission levels high.

Vehicle Pollutants Regulated by Emissions Standards

Vehicle emissions regulations aim to limit certain pollutants that negatively affect air quality and health. Standards aim to cut the harmful emissions that vehicles release.

The most common vehicle pollutants regulated by emissions standards include:

• Carbon monoxide (CO)
• Hydrocarbons (HC)
• Nitrogen oxides (NOx)
• Particulate matter (PM)
• Sulfur dioxide (SO2)

Standards are often measured in grams per mile (g/mi) or grams per kilometer (g/km). This can differ depending on the vehicle class (cars, trucks, buses) and fuel type.

Vehicle Testing: What To Expect

A licensed inspection station or test station must do the vehicle testing. It varies by state, but sites usually include auto repair shops, dealerships, or emissions testing centers. Most of the state links at the end of this article also have test station locations.

In most states, emissions inspections depend on the vehicle's model year. All tests require an equipment check. You might need extra tests depending on the age of the car. For example, a gas cap pressure test may be mandatory for vehicles manufactured after 1973. An Onboard Diagnostic System (OBD) inspection may be necessary for cars made after 1995.

Most vehicle emissions tests include the following inspections:

• Tailpipe emissions
• Fuel cap functionality
• Visual inspection for liquid fuel leaks

It depends on the state, but most vehicle owners must complete emissions testing on a biennial basis (every two years). You can expect to pay $20 to $50 for the emissions test. The cost will increase if the vehicle needs repairs or retests. Some states offer a discount or package price for an emissions test and safety inspection. Some states also provide waivers or aid for eligible low-income motorists.

California Emissions Standards

"California emissions standards" are the regulations established by the California Air Resources Board (CARB) to limit vehicle emissions. These standards are stricter than the federal standards set by the U.S. Environmental Protection Agency (EPA).

California also has a waiver under the Clean Air Act, allowing it to set stricter standards. This is because California has faced more air pollution challenges than other states.

To sell or operate a vehicle in California, it must meet more rigorous emissions standards. This requires automotive manufacturers to produce vehicles with less environmental impact.

The impact of California's emissions standards has expanded beyond the Golden State. Other states can elect to use California's standards instead of federal standards. These 17 U.S. states and districts follow California's emissions standards:

• Colorado
• Connecticut
• Delaware
• Maine
• Maryland
• Massachusetts
• New Jersey
• New Mexico (2011 model year and later)
• New York
• Nevada
• Oregon
• Pennsylvania
• Rhode Island
• Virginia
• Vermont
• Washington (2009 model year and later)
• Washington, D.C.

State Smog Laws

Links to state-specific emissions testing regulations are below:

Need Legal Advice on Vehicle Emissions? Ask a Lawyer

Smog regulations are straightforward and typically don't need legal action. But, some situations are complex, and you may need expert advice. Contact a traffic law attorney in your area for more information. An attorney knowledgeable about your area's smog laws and emissions testing requirements can help.