Texas regulates motor vehicles to assure that vehicles are safe for operation on public roads. Regulations and oversight extend to exhaust systems on vehicles. Texas is unique in that, unlike most states, it does not proscribe a specific decibel level in regards to the exhaust system on vehicles. While there are no specific decibel levels, Texas does regulate the exhaust system properties.
Exhaust System Inspection
Under the Texas Transportation Code, Section 20.15, Texas requires that every motor vehicle be equipped with a muffler, in constant operation, at all times. The muffler must be for the reduction of noise. The muffler must be intact, in condition similar to when new; it cannot have been patched or repaired. Note that exhaust sound decibels are not checked during exhaust inspections so long as the exhaust is not leaking or incomplete.
Texas Code Requirements
Under Section 547.604 of the Texas Transportation Code, all motor vehicles must be equipped with a muffler, in good working order that prevents excessive or unusual noise. Further, the exhaust mufflers may not be bypassed.
Excessive and Unusual
Since Texas lacks specific decibel guidance, "excessive and unusual" is the applicable standard. In Aguilar v. State of Texas, a Texas appellate court reviewed a constitutional challenge claiming that the language was vague, and thus unenforceable since Section 547.604 does not specify a decibel level. The court rejected this challenge, noting that the terms "imply that noise must be outside normal standards for motor vehicles, which ordinary persons can objectively determine."