Measurements of noise emissions

(a) Ambient conditions: (1) Prevailing background sound level: The ambient A weighted sound level at the microphone location as measured in the absence of motor vehicle noise emanating from within the test site, with fast meter response shall be 10 dB(A) lower than the sound level limits specified in section 14-80a-4a which corresponds to the maximum permissible sound level reading which is applicable at the test site at the time of testing. (2) Wind: The wind velocity at the test site shall be measured at the beginning of each series of noise measurements and at intervals of approximately 15 minutes thereafter until it has been established that the wind velocity is essentially determined to be below 12 MPH (19.3 km/h). Once this fact has been established, wind velocity measurements may be made once each hour. Noise measurements shall be made only if the measured wind velocity is 12 MPH (19.3 km/h) or less. (3) Precipitation: Sound level measurements shall not be made under any condition of precipitation; however, measurements may be made with snow on the ground. The ground surface within the triangular measurement area must be free of standing water. (b) Location and operation of sound level system: (1) Microphone location: The microphone shall be located at a height 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 3.5 feet (1.1 m) above the surface on which the microphone stands. When the sound level meter is hand held or otherwise monitored by a person located near the microphone, the holder must orient himself relative to the highway in a manner consistent with the recommendation of the manufacturer of the sound level measuring instrument. The holder or observer shall not be closer than 2 feet (.6 m) from the system's microphone nor shall he locate himself between the microphone and the vehicle being measured. (2) Microphone orientation: The microphone shall be oriented toward the travel 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 instrument does not recommend an angle of orientation for its microphone, the microphone shall be oriented toward the highway at a vertical angle of not less than 70° and not more than perpendicular to the horizontal plane of the traveled lane of the highway. (3) Sound level meter response: The sound level measurement system shall be set to the "A"-weighting network and "fast" meter response mode. (c) Measurement procedure - highway operation: Sound level measurement shall be made of the sound level generated by a motor vehicle or snowmobile operated through the measurement area within the test site, regardless of the highway or surface grade, load, acceleration or deceleration. The sound level generated by the vehicle shall be the highest reading observed on the sound level measurement system as the vehicle passes through the measurement area corrected when appropriate in accordance with section 14-80a-9a. The sound level of the vehicle being measured must be observed to rise at least 6 dB(A) before the maximum sound level occurs and to fall at least 6 dB (A) after the maximum sound level occurs in order to be considered a valid sound level reading. (d) Measurement procedure - stationary test: (1) The motor vehicle or snowmobile shall be parked on the test site as specified in section 14-80a-8a (a) (2). If the motor vehicle is a combination (articulated) vehicle, it shall be parked so that the longitudinal centerline of the towing vehicle and the towed vehicle are in substantial alignment. (2) All auxiliary equipment on the vehicle designed to be operated under normal conditions only when the vehicle is operated at a speed less than 5 MPH (8 km/in) shall be turned off. Examples of such equipment include cranes, asphalt spreaders, liquid or slurry pumps, auxiliary air compressors, welders, and trash compactors. (3) Any motor vehicle equipped with an engine radiator fan automatic clutch system shall be tested with the fan clutch disengaged. (4) With vehicle's transmission in the neutral position* and its clutch (if equipped) engaged, the engine's throttle shall be quickly depressed or advanced to its maximum displacement and immediately released to allow the engine to return to its idle speed. If the vehicle is equipped with an engine speed governor, the engine control shall be advanced to allow the engine to reach its maximum governed speed before returning the throttle control to the engine idle position. Such measurement shall be exclusive of any overshoot in excess of the governed speed. *Snowmobiles not equipped with a "neutral" transmission shift feature will require "blocking" to raise the vehicles drive tread or belt above the test site surface. (5) The maximum reading observed on the sound level measuring instrument occurring during the procedure specified in item (4) above shall be recorded. (6) The procedures specified in items (4) and (5) above shall be repeated until the two maximum sound level readings are noted to be within 2 dB(A) of each other. These two readings shall be numerically averaged and the results shall be used for establishing compliance with this regulation.