[Code of Federal Regulations]
[Title 49, Volume 4]
[Revised as of October 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR325.33]

[Page 795]
 
                        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.
    (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]