Frequently Asked Questions - Noise
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Highway traffic noise is a combination of the sounds produced by a vehicle’s engine and tires that travel along a highway. The level of highway traffic noise primarily depends on three things:
The volume of the traffic
The speed of the traffic
The number of trucks in the flow of the traffic
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The Federal Highway Administration (FHWA) has developed regulations (23 CFR 772) which specify the requirements that highway agencies must follow on federally-funded projects. The Connecticut Department of Transportation (CTDOT) has outlined its implementation of the federal noise regulations in CTDOT’s Highway Traffic Noise Abatement Policy for Projects Funded by the FHWA. This policy has been developed in coordination with FHWA and includes procedures for noise analysis and abatement measures to help protect the public health, welfare, and livability for Connecticut’s residents.
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CTDOT is required by the FHWA noise regulations to perform a traffic noise analysis within the limits of a federally funded project defined as a “Type I” project. Type I projects are federally-funded projects that involve construction of a new highway or adding capacity to or substantially realigning an existing highway. The full definition of a Type I project is provided at 23 CFR 772.
CTDOT constructs and maintains state-owned roads, routes, and interstates. Local or town roads that are maintained by a municipality do not qualify for noise barriers, and residential state roads usually are not feasible for the installation of noise barriers. The first point of contact for the resolution of local noise issues is your local government official. In some towns, the local Department of Health can assist, while in others, you will need to contact Town Hall to identify the appropriate official.
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An existing conditions noise assessment is being conducted under the I-95 Greenwich PEL for data collection purposes only. A formal noise analysis would be conducted during the future National Environmental Policy Act (NEPA) phase for any projects which are identified under the PEL that meet the Type I criteria.
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When planning a highway project, the FHWA Traffic Noise Model uses design and traffic data, including vehicle classification, to predict noise levels during the noisiest hour of the day. The model identifies where impacts will occur based on the predicted noise levels. Once impacts are identified, an analysis will be conducted to determine if a barrier is feasible and reasonable.
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A highway noise barrier is an exterior wall built alongside a roadway or highway that interrupts the flow of sound waves from one area to another. Building a barrier wall is a common approach to mitigating highway traffic noise for nearby residents and businesses. A noise barrier can also be in the form of a berm, which acts the same as a wall but is constructed with earth. A berm, however, requires a large amount of space and is a less common abatement method.
Check out CTDOT’s Noise Barrier Wall Fact Sheet and FHWA’s Keeping the Noise Down brochure for more information.
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Sound travels very much like light. It follows a path over, under, and around things in its path. The farther away one is from the source of sound, the lower the noise due to the sound waves getting larger and losing energy. Noise walls work best if the line of sight is broken from the noise source to the receptor. If there are gaps, the noise will simply travel through that opening like light will illuminate through gaps. If a building is located higher than a noise wall, the noise will travel over the wall to the building. The graphic below shows two examples of noise walls located between buildings and a road. In both cases, the wall will shield one of the houses but will not shield them all. Noise walls do not eliminate noise.
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Other options may also help reduce traffic noise. Some of these may be provided by CTDOT, and others are alternatives that might be considered by private developers or homeowners.
Land use design – if homes are set back from the road or are separated from the road by other development, the noise levels may be lower.
Noise berm (earth or other materials) and combination berm/wall systems
Types of vehicles/speed limits – noise can be reduced with lower speed limits and truck restrictions on a road. However, reducing the speed limit below the appropriate speed based on the design will have only a moderate effect on traffic noise and may actually increase the number of crashes on the roadway.
Building insulation – noise insulation in buildings, such as replacing doors and windows or adding insulation to walls and attics.
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The noise measurements will only be used to validate the FHWA Traffic Noise Model (TNM) and will not be used to assess noise impacts.
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Short-term measurements are selected in residential areas near I-95 that are representative of common noise environments throughout the project corridor. The focus is on areas of frequent outdoor human use, preferably sites that have varying topography that are within 500 feet of the edge of roadway.
Long-term measurements are needed to establish existing ambient conditions where traffic noise from I-95 is not always the dominant noise source. These sites are also selected in residential areas near I-95, but located in areas where other noise sources may raise the “typical” existing levels based on frequency of occurrence and duration. Examples of other noise sources include railroad lines and multi-lane roadways running parallel to I 95.
Guidance Reference: FHWA-HEP-18-065
Noise Measurement Handbook – Final Report; June 1, 2018 https://www.fhwa.dot.gov/environment/noise/measurement/handbook.cfm
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The Study Team has conducted an existing conditions noise analysis as part of the data collection process. However, it is still too early to determine whether noise walls will be proposed or, if proposed, where they will be constructed. The need for and location of noise walls will depend on the projects that advance to the National Environmental Policy Act (NEPA) phase. For Type I projects during the NEPA phase a full noise analysis will determine if the criteria for noise mitigation is met.
In summary, it is too early to make a determination. Stay tuned for updates and consider attending future meetings to learn more as the study progresses.
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The Existing Conditions Noise Analysis Technical Memorandum was released in September 2025 and is available here.