49 CFR § 210.3 - Applicability.
(a) Except as provided in paragraph (b) of this section, the provisions of this part apply to the total sound emitted by moving rail cars and locomotives (including the sound produced by refrigeration and air conditioning units that are an integral element of such equipment), active retarders, switcher locomotives, car coupling operations, and load cell test stands, operated by a railroad as defined in 45 U.S.C. 22, under the conditions described in this part and in 40 CFR part 201.
(b) The provisions of this part do not apply to -
(1) Steam locomotives;
(2) Street, suburban, or interurban electric railways unless operated as a part of the general railroad system of transportation;
(3) Sound emitted by warning devices, such as horns, whistles, or bells when operated for the purpose of safety;
(4) Special purpose equipment that may be located on or operated from rail cars;
(5) As prescribed in 40 CFR 201.10, the provisions of 40 CFR 201.11 (a) and (b) and (c) do not apply to gas turbinepowered locomotives or any locomotive type that cannot be connected by any standard method to a load cell; or
(6) Inert retarders.