23 CFR 772.11 - Analysis of traffic noise impacts.
(a) The highway agency shall determine and analyze expected traffic noise impacts.
(1) For projects on new alignments, determine traffic noise impacts by field measurements.
(2) For projects on existing alignments, predict existing and design year traffic noise impacts.
(b) In determining traffic noise impacts, a highway agency shall give primary consideration to exterior areas where frequent human use occurs.
(c) A traffic noise analysis shall be completed for:
(1) Each alternative under detailed study;
(2) Each Activity Category of the NAC listed in Table 1 that is present in the study area;
(i) Activity Category A. This activity category includes the exterior impact criteria for lands on which serenity and quiet are of extraordinary significance and serve an important public need, and where the preservation of those qualities is essential for the area to continue to serve its intended purpose. Highway agencies shall submit justifications to the FHWA on a case-by-case basis for approval of an Activity Category A designation.
(ii) Activity Category B. This activity category includes the exterior impact criteria for single-family and multifamily residences.
(iii) Activity Category C. This activity category includes the exterior impact criteria for a variety of land use facilities. Each highway agency shall adopt a standard practice for analyzing these land use facilities that is consistent and uniformly applied statewide.
(iv) Activity Category D. This activity category includes the interior impact criteria for certain land use facilities listed in Activity Category C that may have interior uses. A highway agency shall conduct an indoor analysis after a determination is made that exterior abatement measures will not be feasible and reasonable. An indoor analysis shall only be done after exhausting all outdoor analysis options. In situations where no exterior activities are to be affected by the traffic noise, or where the exterior activities are far from or physically shielded from the roadway in a manner that prevents an impact on exterior activities, the highway agency shall use Activity Category D as the basis of determining noise impacts. Each highway agency shall adopt a standard practice for analyzing these land use facilities that is consistent and uniformly applied statewide.
(v) Activity Category E. This activity category includes the exterior impact criteria for developed lands that are less sensitive to highway noise. Each highway agency shall adopt a standard practice for analyzing these land use facilities that is consistent and uniformly applied statewide.
(vi) Activity Category F. This activity category includes developed lands that are not sensitive to highway traffic noise. There is no impact criteria for the land use facilities in this activity category and no analysis of noise impacts is required.
(vii) Activity Category G. This activity includes undeveloped lands.
(A) A highway agency shall determine if undeveloped land is permitted for development. The milestone and its associated date for acknowledging when undeveloped land is considered permitted shall be the date of issuance of a building permit by the local jurisdiction or by the appropriate governing entity.
(B) If undeveloped land is determined to be perrmitted, then the highway agency shall assign the land to the appropriate Activity Category and analyze it in the same manner as developed lands in that Activity Category.
(C) If undeveloped land is not permitted for development by the date of public knowledge, the highway agency shall determine noise levels in accordance with 772.17(a) and document the results in the project's environmental clearance documents and noise analysis documents. Federal participation in noise abatement measures will not be considered for lands that are not permitted by the date of public knowledge.
(d) The analysis of traffic noise impacts shall include:
(1) Identification of existing activities, developed lands, and undeveloped lands, which may be affected by noise from the highway;
(2) For projects on new or existing alignments, validate predicted noise level through comparison between measured and predicted levels;
(3) Measurement of noise levels. Use an ANSI Type I or Type II integrating sound level meter;
(4) Identification of project limits to determine all traffic noise impacts for the design year for the build alternative. For Type II projects, traffic noise impacts shall be determined from current year conditions;
(e) Highway agencies shall establish an approach level to be used when determining a traffic noise impact. The approach level shall be at least 1 dB(A) less than the Noise Abatement Criteria for Activity Categories A to E listed in Table 1 to part 772;
(f) Highway agencies shall define substantial noise increase between 5 dB(A) to 15 dB(A) over existing noise levels. The substantial noise increase criterion is independent of the absolute noise level.
(g) A highway agency proposing to use Federal-aid highway funds for a Type II project shall perform a noise analysis in accordance with § 772.11 of this part in order to provide information needed to make the determination required by § 772.13(a) of this part.