Subchapter E. MEASUREMENT OF NOISE EMISSION HIGHWAY
OPERATIONS
Sec.
157.41. Site characteristics.
157.42. Ambient conditions.
157.43. Location and operation of sound level measurement system.
157.44. Measurement procedures.§ 157.41. Site characteristics.
(a) Distances. Measurement shall be made at a test site which is adjacent to, and includes a portion of, a traveled lane of a public highway. A microphone target point shall be established on the centerline of the traveled lane of the highway, and a microphone location point shall be established on the ground surface not less than 26 feet (7.8 meters) or more than 118 feet (35.4 meters) from the microphone target point and on a line that is perpendicular to the centerline of the traveled lane of the highway and that passes through the microphone target point. In the case of a standard test site, the microphone location point shall be 50 feet (15.2 meters) from the microphone target point. Within the test site shall be a triangular measurement area. A plan view diagram of a standard test site, having an open site within a 50 foot (15.2 meters) radius of both the microphone target point and the microphone location point, is shown in Figure 1 in Appendix A. Measurements may be made at a test site having smaller or greater dimensions in accordance with the provisions of Subchapter F (relating to correction factors).
(b) Sound reflective objects in triangular measurement areas. The test site shall be an open site, essentially free of large sound-reflecting objects. However, the following objects may be within the test site, including the triangular measurement area:
(1) Small cylindrical objects such as fire hydrants or telephone or utility poles.
(2) Rural mailboxes.
(3) Traffic railings of any type of construction except solid concrete barriers. See § 157.2 (relating to definitions).
(4) One or more curbs having a vertical height of one foot (0.3 meter) or less.
(c) Sound reflective objects outside triangular measurement area. The following objects may be within the test site if they are outside of the triangular measurement area of the site:
(1) Any vertical surface, such as billboard, regardless of size, having a lower edge more than 15 feet (4.6 meters) higher than the surface of the traveled lane of the highway.
(2) Any uniformly smooth sloping surface slanting away from the highway, such as a rise in grade alongside the highway, with a slope that is less than 45° above the horizontal.
(3) Any surface slanting away from the highway that is 45° or more and not more than 90° above the horizontal, if all points on the surface are more than 15 feet (4.6 meters) above the surface of the traveled lane of the highway.
(d) Surface. The surface of the ground within the measurement area shall be relatively flat. The site shall be a ‘‘soft’’ test site. However, if the site is determined to be ‘‘hard,’’ the correction factor shall be applied to the measurement.
(e) Pavement. The traveled lane of the highway within the test site shall be dry, paved with relatively smooth concrete or asphalt, and substantially free of:
(1) holes or other defects which would cause a motor vehicle to emit irregular tire, body, or chassis impact noise; and
(2) loose material, such as gravel or sand.
(f) Tunnel or underpass. The traveled lane of the highway on which the microphone target point is situated shall not pass through a tunnel or underpass located within 200 feet (61 meters) of that point.
§ 157.42. Ambient conditions.
(a) Sound. Requirements concerning ambient sound conditions shall be as follows:
(1) 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 noise zone, with fast meter response using a sound level measurement system that conforms to the provisions of § 157.31 (relating to types of measurement systems which may be used).
(2) The measured ambient level shall be ten decibels (A) or more below that level specified in 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 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 shall only be made if the measured wind velocity is 12 miles per hour (19.3 kilometers per hour) or less. Gust wind measurements of up to 20 miles per hour (33.2 kilometers per hour) shall be allowed.
(c) Precipitation. Measurements shall be prohibited under any condition of precipitation, however, measurements may be made with snow on the ground. The ground surface within the measurement area shall be free of standing water.
§ 157.43. Location and operation of sound level measurement system.
(a) Microphone height. The microphone of a sound level measurement system that conforms to the provisions of § 157.31 (relating to types of measurement systems which may be used) shall be located at a height of not less than 2 feet (0.6 meters) nor more than 6 feet (1.8 meters) above the plane of the roadway surface and not less than 3 1/2 feet (1.1 meters) and not more than 4 1/2 feet (1.4 meters) above the surface on which the microphone stands. The preferred microphone height or flat terrain is four feet (1.2 meters).
(b) Monitor orientation. Requirements for monitor orientation shall be as follows:
(1) When the sound level measurement system is hand-held or is otherwise monitored by a person located near its microphone, the holder shall orient himself 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 (0.6 meters) from the microphone of the system, nor shall he locate himself between the microphone and the vehicle being measured.
(c) Microphone orientation. 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 manufacturer of the system. 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° and not more than perpendicular to the horizontal plane of the traveled lane of the highway at the microphone target point.
(d) Network and response mode. The sound level measurement system shall be set to the A-weighting network and ‘‘fast’’ meter response mode.
§ 157.44. Measurement procedures.
(a) Conditions. In accordance with the provisions of this section, a measurement shall be made of the sound level generated by a motor vehicle operating through the measurement area on the traveled lane of the highway within the test site, regardless of the highway grade, load, acceleration or deceleration.
(b) Maximum sound level reading. The second level generated by the motor 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 the provisions of Subchapter F (relating to correction factors).
Table 1 lists the range of maximum permissible sound level readings for various readings for various test conditions.
The sound level of the vehicle being measured shall be observed to rise at least six decibels (A) before the maximum sound level occurs and to fall at least six decibels (A) after the maximum sound level occurs in order to be considered a valid sound level reading.
Cross References This section cited in 67 Pa. Code § 157.51 (relating to microphone distance correction factors).
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