[Code of Federal Regulations]

[Title 49, Volume 5]

[Revised as of October 1, 2005]

From the U.S. Government Printing Office via GPO Access

[CITE: 49CFR325.55]



[Page 14]

 

                        TITLE 49--TRANSPORTATION

 

                      DEPARTMENT OF TRANSPORTATION

 

PART 325_COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS

--Table of Contents

 

        Subpart E_Measurement of Noise Emissions; Stationary Test

 

Sec. 325.55  Ambient conditions; stationary test.



    (a)(1) Sound. The ambient A-weighted sound level at the microphone 

location point shall be measured, in the absence of motor vehicle noise 

emanating from within the clear zone, with fast meter response using a 

sound level measurement system that conforms to the rules of Sec. 

325.23.

    (2) The measured ambient level must be 10 dB(A) or more below that 

level specified in Sec. 325.7, Table 1, which corresponds to the 

maximum permissible sound level reading which is applicable at the test 

site at the time of testing.

    (b) Wind. The wind velocity at the test site shall be measured at 

the beginning of each series of noise measurements and at intervals of 

5-15 minutes thereafter until it has been established that the wind 

velocity is essentially constant. Once this fact has been established, 

wind velocity measurements may be made at intervals of once every hour. 

Noise measurements may only be made if the measured wind velocity is 12 

mph (19.3 kph) or less. Gust wind measurements of up to 20 mph (33.2 

kph) are allowed.

    (c) Precipitation. Measurements are prohibited under any conditions 

of precipitation, however, measurements may be made with snow on the 

ground. The ground within the measurement area must be free of standing 

water.



[40 FR 42437, Sept. 12, 1975, as amended at 41 FR 28267, July 9, 1976]