According to Federal Guidelines:
[Code of Federal Regulations]
[Title 49, Volume 4]
[Revised as of October 1, 2001]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR325.91]
[Page 727]
TITLE 49--TRANSPORTATION
CHAPTER III--FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION,
DEPARTMENT OF TRANSPORTATION
PART 325--COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS--Table of Contents
Subpart G--Exhaust Systems and Tires
Sec. 325.91 Exhaust systems.
A motor vehicle does not conform to the visual exhaust system
inspection requirements, 40 CFR 202.22, of the Interstate Motor Carrier
Noise Emission Standards, if inspection of the exhaust system of the
motor vehicle discloses that the system--
(a) Has a defect which adversely affects sound reduction, such as
exhaust gas leaks or alteration or deterioration of muffler elements,
(small traces of soot on flexible exhaust pipe sections shall not
constitute a violation of this subpart);
(b) Is not equipped with either a muffler or other noise dissipative
device, such as a turbocharger (supercharger driven by exhaust gases);
or
(c) Is equipped with a cut-out, by-pass, or similar device, unless
such device is designed as an exhaust gas driven cargo unloading system.
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