[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: 49CFR325.37]



[Page 12-13]

 

                        TITLE 49--TRANSPORTATION

 

                      DEPARTMENT OF TRANSPORTATION

 

PART 325_COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS

--Table of Contents

 

      Subpart D_Measurement of Noise Emissions; Highway Operations

 

Sec. 325.37  Location and operation of sound level measurement system; 

highway operations.



    (a) The microphone of a sound level measurement system that conforms 

to the rules in Sec. 325.23 of this part shall be located at a height 

of not less than 2 feet (.6 m) nor more than 6 feet (1.8 M) above the 

plane of the roadway surface and not less than 3\1/2\ feet (1.1 m) above 

the surface on which the microphone stands. The preferred microphone 

height on flat terrain is 4 feet (1.2 m).

    (b)(1) When the sound level measurement system is hand-held or is 

otherwise monitored by a person located near its microphone, the holder 

must orient himself/herself relative to the highway in a manner 

consistent with the recommendation of the manufacturer of the sound 

level measurement system.

    (2) In no case shall the holder or observer be closer than 2 feet 

(.6 m) from the system's microphone, nor shall he/



[[Page 13]]



she locate himself/herself between the microphone and the vehicle being 

measured.

    (c) The microphone of the sound level measurement system shall be 

oriented toward the traveled lane of the highway at the microphone 

target point at an angle that is consistent with the recommendation of 

the system's manufacturer. If the manufacturer of the system does not 

recommend an angle of orientation for its microphone, the microphone 

shall be oriented toward the highway at an angle of not less than 70 

degrees and not more than perpendicular to the horizontal plane of the 

traveled lane of the highway at the microphone target point.

    (d) The sound level measurement system shall be set to the A-

weighting network and ``fast'' meter response mode.



[40 FR 42437, Sept. 12, 1975, as amended at 41 FR 10227, Mar. 10, 1976]