Noise Analysis

New Hampshire has been evaluating the public impact of increased highway traffic noise since the development of the National Environmental Policy Act of 1969 (NEPA). The act required, amongst other aspects, evaluation of the impacts associated with improved and newly constructed roadways. The first noise abatement structure in New Hampshire was built in 1977 along Interstate 93 in Manchester. Since then numerous additional structures have been added throughout the state.

Abatement Eligibility
Noise abatement in New Hampshire is generally in the form of a sound barrier or berm. The locations of these barriers are carefully selected based on their ability to meet a set of specific criteria set forth by the NH Department of Transportation (NH DOT) and the Federal Highway Administration (FHWA). An area is not considered eligible unless it meets ALL of the criteria set forth in the Department's Noise Policy. The following are highlights of the criteria found in the Department's Noise Policy:

• Type I Project - NH DOT can only consider an area eligible for noise abatement when impacts are associated with a Type I project. Type I projects are generally those which involve the addition of a new roadway, or the physical alteration of an exiting roadway. Type II projects are those designed solely for the purpose of traffic noise abatement in areas where no highway improvements are scheduled. NH DOT does not have a Type II noise policy and therefore cannot conduct these types of projects. In order for an area to be considered eligible for noise abatement, there MUST be a Type I project scheduled in its immediate vicinity.
• Decibel Level - An area zoned residential is considered for protection when traffic noise levels reach or exceed 66 decibels (dBA). Areas zoned commercial are considered eligible if noise levels reach or exceed 71 dBA.
• Feasibility - An minimum of a 5 dBA insertion loss must be expected for each identified receptor (home or business) in order for an area to be considered eligible for noise abatement. Despite this regulation NH DOT generally makes every reasonable effort to obtain a 10 dBA decrease in sound levels after construction is completed. For safety and stability reasons, the structural portions of a barrier should not be in excess of 25 feet in height. Impacts to wetlands, endangered species, historic resources, recreational facilities and other area resources can also effect the feasibility of a particular abatement measure.
• Reasonableness:
  • Cost Effectiveness - NH DOT currently projects that the cost of noise barrier construction is $30 per square foot. If the anticipated cost per benefiting receptor is expected to exceed $45,000 abatement measure will not be considered reasonable. Reasonableness is also determined by calculating the protective surface area per benefited receptor of a barrier or berm. If the anticipated square footage per benefitted receptor is expected to exceed 1,500 square feet the abatement measure will not be considered reasonable.
  • Noise Reduction Design Goal - In order for an abatement measure to be considered reasonable, it must be able to provide at least a 7 dBA noise reduction for at least 1 benefited receptor.
  • Views of the benefited receptors - Viewpoints from the entire project community, including benefited receptors, will be solicited for noise impacts and any noise abatement alternatives. If no objections to the proposed noise abatement are found at this level of public involvement, then the noise barrier will be deemed reasonable. If objections are identified, at least 51% of the total possible receptors (property owners and tenants) recieving at least a 5 dBA or greater noise reduction must be in support of an abatement alternative for it to be considered reasonable.
• Development History - In order for a property to be evaluated for noise impacts it must contain development which is already in place or is permited for development (as indicated by the issuance of a building permit or similar final approval from the local municipality) by the date of public knowledge (the date upon which design approvals are granted by the FHWA or NHDOT).

Additional Information:

• 1996 NHDOT Noise Policy - For projects approved prior to July 13, 2011
• 2011 NHDOT Noise Policy - For Projects approved on or after July 13, 2011
• FHWA Traffic Noise Information
• AASHTO Center for Environmental Excellence - Noise

Contacts:

• Charlie Hood - Administrator
• Jon Evans - Senior Environmental Manager