Programs

When and Why CDOT Builds Noise Mitigation

Most highway noise abatement (e.g., noise barriers) in Colorado are built by CDOT as a result of a Federal regulation (Title 23 Code of Federal Regulation Part 772 [23 CFR 772]: Procedures for Abatement of Highway Traffic Noise and Construction Noise). Other noise barriers are built by private developers, local government agencies, and private citizens.

In order for an area to qualify for noise abatement to be built by CDOT, the following steps must be followed:

  1. CDOT must plan to do a construction project in the area.
  2. The project is classified as being either Type I or Type III. Project types are defined in 23 CFR 772.5. Only Type I projects are analyzed for potential noise mitigation. Examples include adding through-traffic lanes or completing partial interchanges. Projects such as repaving or adding turn lanes are classified as Type III.
  3. Noise analysis is conducted for all Type I projects to determine if any receptors (e.g., homes, schools, parks, offices) will be impacted due to the proposed construction project. "Impact" is defined as specific levels of noise for different types of receptors by the CDOT Noise Analysis and Abatement Guidelines. "Impact" is also defined as a noise increase at least 10 decibels from existing conditions to 20 years in the future.
  4. If analysis shows that any receptors are impacted, the feasibility and reasonableness of noise mitigation is analyzed. In order for CDOT to recommend noise mitigation, the mitigation must be shown to be feasible and reasonable.
  5. Feasibility has to do with constructability. This primarily deals with engineering considerations (e.g., can a barrier be built given the topography of the location; can a substantial noise reduction be achieved given certain access, drainage, safety, or maintenance requirements; are other predominating noise sources present in the area). In addition, the barrier must be able to reduce noise for at least one receptor by at least 5 dBA and noise walls must have a height of 20 feet or less.
  6. Reasonableness has to do with socio-economic factors and must meet the following three criteria: (1) The barrier must reduce noise by 7 dBA or more for at least one receptor. (2) The barrier must cost no more than $6,800 per receptor per decibel of reduction; this is approximately equal to $48,000 per receptor. (3) At least 50 percent of the receptors that will receive benefit from the barrier must be in favor. Prior to construction, all benefited property owners and residents would be surveyed.

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