Highway Traffic Noise

Noise Sensitive Land Uses

Noise sensitive land uses are properties where there is frequent human use that might be impacted by traffic noise levels that approach, meet, or exceed the Noise Abatement Criteria (NAC) – levels established by the FHWA at which abatement must be considered (as required by 23 CFR 772). Typical noise sensitive land uses include residences, schools, places of worship, commercial properties with outdoor areas of use, and recreational areas. If a noise sensitive land use’s future noise levels are predicted to meet, approach, or exceed the NAC, the noise sensitive land use is considered impacted. Noise sensitive land uses are also considered impacted when a substantial increase (i.e., 15 dB[A], as defined by FDOT) in highway traffic noise is predicted to occur as a direct result of a transportation project. A substantial increase typically occurs in areas where traffic noise is a minor component of the existing noise environment but would become a major component after the project is constructed (e.g., new alignment project). 

Noise Abatement Measures

Noise abatement is considered at all impacted noise sensitive land uses for which there is a NAC.  Abatement measures considered include traffic management, alignment modifications, noise buffer zones through application of land use controls and noise barriers.

Noise barriers reduce noise levels by blocking the sound path between a highway and noise sensitive site. To effectively reduce traffic noise, a barrier must be relatively long, continuous (with no openings), and of sufficient height.

For a noise barrier to be considered feasible and cost reasonable, the following conditions must be met:

• At least two impacted receptors must be provided a noise reduction of 5 dB(A) or more to be considered feasible.

• A noise barrier must also attain the Noise Reduction Design Goal (NRDG) of 7 dB(A) for at least one benefited receptor.

  • Of importance, this receptor may also have been previously identified as meeting the feasibility requirement of receiving a 5 dB(A) reduction (first bullet).

• The cost of the noise barriers should not exceed $64,000 per benefited receptor.

  • This is the upper cost limit established by FDOT (2024).

  • A benefited receptor is defined as a recipient of an abatement measure that experiences at least a 5 dB(A) reduction as a result of providing a noise barrier.

  • The current unit cost used to evaluate cost reasonableness is $40 per square foot (sq. ft.).

• The noise barrier must meet design/construction, safety, access, right-of-way, maintenance, drainage and utility criteria to be considered feasible.

• The viewpoint of the property owner of the benefited noise sensitive land uses is considered.

Noise Metrics

Noise levels developed for FDOT highway traffic noise analyses are expressed in decibels (dB) using an “A”-scale [dB(A)] weighting. This scale most closely approximates the response characteristics of the human ear to typical traffic noise levels.  Reported noise levels are reported as hourly equivalent noise levels [Leq(h)]. The Leq(h) is defined as the equivalent steady-state sound level that, in an hourly period, contains the same acoustic energy as the time-varying sound level for the same hourly period. Use of these metrics is consistent with the requirements of 23 CFR 772.

Sources:

23 Code of Federal Regulations Part 772 (23 CFR 772), "Procedures for Abatement of Highway Traffic Noise and Construction Noise", Federal Register, Vol. 75, No. 133, Tuesday, July 13, 2010; pages 39834‐39839.

FDOT, "Highway Traffic Noise", Part 2, Chapter 18. Project Development and Environment Manual, FDOT, Tallahassee, July 1, 2023.