Worse than that are statutes that effectively limit the use of all aftermarket exhausts, such as "no person shall modify the exhaust system of a motor vehicle in any manner which will amplify or increase the noise or sound emitted louder than that emitted by the muffler originally installed on the vehicle." While that doesn't specifically prohibit all modification, it also doesn't provide any means of measuring whether a vehicle has been acceptably modified. Such language also negatively affects the aftermarket industry by placing the noise limit authority in the hands of the OEMs and ignores the fact that aftermarket exhaust systems are designed to increase power and make vehicles run more efficiently without increasing emissions.

Previous California law allowed modifications so long as the noise levels did not exceed the 95dB limit, however, the roadside enforcement of this limit was chaotic, leading to subjective, selective, and improper enforcement. Enforcement resulted in many drivers being pulled over by state and local police and cited for improper modified exhaust systems despite having what they believed to be legal aftermarket exhausts. To illustrate the issue, SEMA conducted a series of exhaust noise tests in April of 2001. First they contacted California SAN members to see how many had received citations for excessive or modified exhaust and then invited them to have their cars tested to see if they actually complied with California law. Working with a board-certified acoustical engineer and performing the test according to the standards set out in California law, SEMA discovered only one of the cars actually exceeded the 95db legal level.

To remedy this problem, in 2002 SEMA helped enact a new procedure in California that uses an objectively measured standard in a fair and predictable test. The result was that those with legally modified exhaust systems can confirm that they comply with California's exhaust noise standard at the 40 smog check stations statewide that provide referee functions provided that they emit no more than 95 dB during the SAE test procedure. A similar standard was enacted in Maine in 2003, and Montana in 2007. Nevertheless, only those who have received a citation for exhaust noise violation can submit their vehicle for the test.

Tires & Fuel Efficiency
It's no secret that the choice of tires can alter a vehicle's rolling resistance, but those same choices can also result in a more responsive and better handling vehicle with increased wet and/or dry traction and safety. Currently, both California and the federal government are pursuing regulations to rate replacement tires for fuel efficiency in an effort to influence consumer choice. In theory, if a tire is more fuel efficient, less gas is burned, and therefore less CO2 is emitted into the atmosphere.

The NHTSA is drafting a consumer information system to rate the fuel economy, safety, and durability characteristics of most replacement tires. NHTSA has established test procedures for determining tire ratings, but is still considering options on how to convey the information to buyers. In the current proposal, companies that produce 15,000 units or less in a tire line (mostly classic, antique, or off-highway tires) are exempted.

The premise for the new program is to allow consumers to compare ratings for different replacement tires and determine the effect of tire choices on fuel economy or the potential trade-offs between tire fuel efficiency (rolling resistance), safety (wet traction), and durability (treadwear life). The information would be conveyed in the form of a rating system for each category, which appears on a label affixed to each tire.

California is pursuing a variation on the federal program whereby state regulators could assign a "fuel efficient tire" ranking to the top 15 percent of tires with the lowest rolling resistance within their size and load class. All other tested tires would be ranked as "not fuel efficient," however the 15,000 or less exemption would still apply.