[Code of Federal Regulations]
[Title 49, Volume 4]
[Revised as of October 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR325.79]

[Page 801]
 
                        TITLE 49--TRANSPORTATION
 
                      DEPARTMENT OF TRANSPORTATION
 
PART 325_COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS
--Table of Contents
 
                      Subpart F_Correction Factors
 
Sec. 325.79  Application of correction factors.

    (a) If two correction factors apply to a measurement they are 
applied cumulatively.
    (b) The following examples illustrate the application of correction 
factors to sound level measurement readings:
    (1) Example 1--Highway operations. Assume that a motor vehicle 
generates a maximum observed sound level reading of 86 dB(A) during a 
measurement in accordance with the rules in subpart D of this part. 
Assume also that the distance between the microphone location point and 
the microphone target point is 60 feet (18.3 m) and that the measurement 
area of the test site is acoustically ``hard.'' The corrected sound 
level generated by the motor vehicle would be 85 dB(A), calculated as 
follows:

 86 dB(A) Uncorrected reading
+1 dB(A) Distance correction factor
-2 dB(A) Ground surface correction factor
----------
 85 dB(A) Corrected reading

    (2) Example 2--Stationary test. Assume that a motor vehicle 
generates maximum sound level readings which average 88 dB(A) during a 
measurement in accordance with the rules in subpart E of this part. 
Assume also that the distance between the microphone location point and 
the microphone target point is 35 feet (10.7 m), and that the 
measurement area of the test site is acoustically ``soft.'' The 
corrected sound level generated by the motor vehicle would be 87 dB(A), 
calculated as follows:

 88 dB(A) Uncorrected average of readings
-3 dB(A) Distance correction factor
+2 dB(A) Ground surface correction factor
----------

 87 dB(A) Corrected reading