[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: 49CFR325.33]



[Page 11-12]

 

                        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. 325.33  Site characteristics; highway operations.



    (a) 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 31 feet (9.5 m) or more 

than 83 feet (25.3 m) 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 is 50 feet (15.2 

m) from the microphone target point. Within the test site is a 

triangular measurement area. A plan view diagram of a standard test 

site, having an open site within a 50-foot (15.2 m) radius of both the 

microphone target point and the microphone location point, is shown in 

Figure 1. Measurements may be made at a test site having smaller or 

greater dimensions in accordance with the rules in subpart F of this 

part.

[GRAPHIC] [TIFF OMITTED] TC01AP91.010



    (b) The test site must 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.



[[Page 12]]



    (3) Traffic railings of any type of construction except solid 

concrete barriers (see Sec. 325.5(c)(4)).

    (4) One or more curbs having a vertical height of 1 foot (.3 m) or 

less.

    (c) 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 m) 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 degrees above the horizontal.

    (3) Any surface slanting away from the highway that is 45 degrees or 

more and not more than 90 degrees above the horizontal, if all points on 

the surface are more than 15 feet (4.6 m) above the surface of the 

traveled lane of the highway.

    (d) The surface of the ground within the measurement area must be 

relatively flat (see Sec. 325.5(c)(5)). The site shall be a ``soft'' 

test site. However, if the site is determined to be ``hard,'' the 

correction factor specified in Sec. 325.75(a) of this part shall be 

applied to the measurement.

    (e) The traveled lane of the highway within the test site must 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) The traveled lane of the highway on which the microphone target 

point is situated must not pass through a tunnel or underpass located 

within 200 feet (61 m) of that point.



[40 FR 42437, Sept. 12, 1975, as amended at 54 FR 50385, Dec. 6, 1989]