The National Environmental Policy Act (NEPA) of 1969 and the Federal-Aid Highway Act of 1970 control the evaluation of highway traffic noise impacts. They require environmental evaluation of federal or federal-aid highway projects, and reasonable and feasible mitigation of identified impacts. Also, on May 14, 1976, the Federal Highway Administration (FHWA) publicly stated that local governments must help control noise impacts through noise-compatible land-use planning and zoning.
The Federal Highway Administration (FHWA) highway traffic noise regulation 23 CFR 772 requires the following during the planning and design of a highway project:
The regulation requires that FHWA make every feasible and reasonable effort to provide substantial noise reduction when highway traffic noise impacts occur. Compliance with 23 CFR 772 is a State prerequisite for receiving Federal-aid highway funds for construction or reconstruction of a highway.
HIGHWAY TRAFFIC NOISE ANALYSIS
The Maryland Department of Transportation State Highway Administration State Highway Administration (MDOT SHA) conducts noise analysis for
Type I projects as part of the NEPA process. A typical traffic noise analysis includes:
Determination of Existing Noise LevelsMDOT SHA does a noise measurement to determine the existing noise level in an area. It is important to determine the source of the noise, as there may be non-highway noise sources, especially in commercial areas.
The goal is to establish a baseline for assessing the impact of highway traffic noise. In assessing traffic noise impact, the relationship of existing noise to predicted future noise levels is a factor.
Prediction of Future Noise LevelsBased on the proposed highway alignment, MDOT SHA uses a computer program developed by the Federal Highway Administration (FHWA) to forecast the level of noise in the design year, which is typically about 20 years in the future. The computer program uses predicted loudest-hour (worst-case) traffic volumes, the percentage of trucks, and travel speeds to forecast noise levels.
Contrary to popular belief, the worst source of highway noise is not typically a traffic jam. When there is a traffic jam, vehicles do not move as fast as they normally would if there was no jam, and therefore do not make as much noise. The level of service (LOS) of a roadway describes the operating conditions on the facility in terms of traffic performance measures related to speed and travel time, freedom to maneuver, traffic interruptions, comfort and convenience. Levels of service range from LOS A (least congested) to LOS F (most congested) as shown below:
LEVELS OF SERVICEAdapted from
A Policy on Geometric Design of Highways and Streets. AASHTO. 2001Highway traffic noise is worst in LOS D — this is when the roadway is nearing capacity. Although vehicles may not be moving quickly, they are all moving and are doing so at a steady speed. This is the point at which any more vehicle additions will result in an unstable flow of traffic (stop-and-go traffic).
The computer program also examines distance of the receptors from the proposed highway and physical features such as hills, valleys, buildings, and obstructions that affect how noise would travel to the receptors.
The most recent computer program developed by the FHWA is
TNM (Traffic Noise Model) Version 2.5, available through the McTrans Center at the University of Florida.
Determination of Noise Impact'Sensitive noise receptors' — residences, schools, houses of worship, and historic sites — are strongly affected by traffic noise if:
Evaluation of Noise Abatement AlternativesIf noise impacts are identified, MDOT SHA considers noise abatement to minimize or eliminate impacts from the project.
This impact alone does not determine that abatement will be implemented. All criteria, as set forth in the
MDOT SHA Sound Barrier Policy, must be met before abatement is considered reasonable and feasible.
Abatement may or may not be in the form of a noise barrier. MDOT SHA determines the specific form of noise abatement on a site-by-site basis, and can be influenced by the use or activity that is affected.
MDOT SHA takes noise measurements for the following reasons:
Environmental noise measurements can only be taken under favorable weather conditions.
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