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  • § 325.1
    Scope of the rules in this part.
  • § 325.3
    Effective date.
  • § 325.5
    Definitions.
  • § 325.7
    Allowable noise levels.
  • § 325.9
    Measurement tolerances.
  • § 325.11
    Issuance, amendment, and revocation of the rules in this part.
  • § 325.13
    Inspection and examination of motor vehicles.
  • § 325.21
    Scope of the rules in this subpart.
  • § 325.23
    Type of measurement systems which may be used.
  • § 325.25
    Calibration of measurement systems.
  • § 325.27
    Use of a windscreen.
  • § 325.31
    Scope of the rules in this subpart.
  • § 325.33
    Site characteristics; highway operations.
  • § 325.35
    Ambient conditions; highway operations.
  • § 325.37
    Location and operation of sound level measurement system; highway operations.
  • § 325.39
    Measurement procedure; highway operations.
  • § 325.51
    Scope of the rules in this subpart.
  • § 325.53
    Site characteristics; stationary test.
  • § 325.55
    Ambient conditions; stationary test.
  • § 325.57
    Location and operation of sound level measurement systems; stationary test.
  • § 325.59
    Measurement procedure; stationary test.
  • § 325.71
    Scope of the rules in this subpart.
  • § 325.73
    Microphone distance correction factors.
  • § 325.75
    Ground surface correction factors.
  • § 325.77
    Computation of open site requirements—nonstandard sites.
  • § 325.79
    Application of correction factors.
  • § 325.91
    Exhaust systems.
  • § 325.93
    Tires.

Part 325
COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS

§ 325.9: Measurement tolerances.

(a) Measurement tolerances will be allowed to take into account the effects of the following factors:
(1) The consensus standard practice of reporting filed sound level measurements to the nearest whole decibel.
(2) Variations resulting from commercial instrument tolerances.
(3) Variations resulting from the topography of the noise measurement site.
(4) Variations resulting from atmospheric conditions such as wind, ambient temperature, and atmospheric pressure.
(5) Variations resulting from reflected sound from small objects allowed within the test site.
(6) The interpretation of the effects of the above cited factors by enforcement personnel.
(b) Measurement tolerances shall not exceed 2 decibels for a given measurement.