Federal law prohibits states from issuing motor vehicle safety regulations that conflict with federal standards. This is called federal preemption. However, states are free to enact and enforce safety and equipment regulations, which are identical to the FMVSS or, in the absence of a federal rule, establish their own laws and regulations. The most frequent examples of individual state rules cover parts like "optional" or "accessory" lighting equipment, noise levels for exhaust and stereo systems, suspension height, and window tinting. States also establish rules on how a vehicle is titled and registered. State and local jurisdictions have authority to regulate inoperable vehicles or determine whether an enthusiast is engaged in a business versus a private activity. State and local law enforcement officials issue tickets and inspect cars.

State laws have evolved over many generations and they continue to change. Some laws are better than others, and there is a constant need to remind state policy makers not to be biased in favor of the vehicle's original equipment, such as lighting, tires and wheels, suspension components, and bumper/frame height. For example, some state laws allow motorists to be ticketed when an officer has made a subjective noise level determination that the exhaust system is "louder than what came with the car." To cite another example, bills have been introduced in state legislatures to ban spinners even though they are legal at the federal level. Opposing arbitrary and unnecessarily restrictive equipment and inspection laws is a constant challenge.

Exhaust Noise
How Loud is too Loud?
Imagine driving down the road and getting stopped for the modified muffler on your hot rod. Now imagine sitting on the shoulder, receiving a citation from local law enforcement, while a stock Ferrari overtakes your car and drives on. This is the scene being played on state highways across the country, the result of poorly drafted or ineffective state laws and regulations. The laws on the books in these states frequently cite the manufacturer's specifications or a factory-installed muffler as the basis on which vehicle exhaust noise is measured.

On this topic, states can generally be divided into two major categories: states with noise standards and states without noise standards. Of the states with a test standard on the books, many ignore guidelines when handing out citations. Most states that have chosen to go the route of setting specifications choose to measure a vehicle's noise by decibels. States that have quantifiable noise standards on the books are shaded red in the map (at left). These standards often go unenforced. One reason these regulations are not enforced is that they are based on an in-use standard-exhaust noise is measured while a vehicle is in motion on the highway. The states that employ these operating standards typically divide vehicles into classes and then set separate standards: one for vehicles while driving on roads with a speed limit of 35 mph or less and a second standard for vehicles driving on roadways with a speed limit greater than 35 mph. The measurements are to be taken while the vehicle is in motion on the road, usually from a distance of 50 feet from the center lane of travel.

Other states choose not to specify a quantifiable noise standard. These states are shown in yellow in the map. Typical language in these states' statutes includes prohibitions on "excessive or unusual noise" from a vehicle's exhaust system. While most motorists believe that exhaust systems should not be used in a way that causes overly loud or objectionable noise, these vague provisions fail to provide a clear and objective standard for those seeking more durable exhaust systems that enhance a vehicle's appearance and increase performance.