What is illegal regarding vehicle muffler systems?

Bypassing or cutting out a motor vehicle's muffler system is illegal because it can lead to increased noise pollution and violate state emissions regulations. Mufflers are designed not only to reduce noise but also to help control harmful emissions from the vehicle. Altering or removing the muffler system can result in a vehicle that is excessively loud and does not comply with environmental regulations, which are in place to protect public health and the environment.

While installing a high-performance muffler or using one that may be louder than factory specifications could potentially cause issues, as long as they meet legal requirements, these actions are generally permissible. Removing the muffler altogether, although it is a similar alteration, is also considered illegal as it directly affects the vehicle’s ability to meet noise and emissions standards. Therefore, bypassing or cutting out the system stands out as specifically illegal due to the potential repercussions on vehicle noise levels and its emissions profile.