Illinois Department of Transportation, Erica Borggren, Acting Secretary
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Patrick J. Quinn, Governor
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It is the policy of the Illinois Department of Transportation (IDOT) to assess traffic noise impacts on proposed transportation projects such as highways on new location or the addition of through travel lanes. Land uses evaluated for noise impacts include residential areas, schools, libraries, and parks or other recreational areas which may be affected by highway traffic noise. During the project development stage traffic noise studies are performed. The Federal Highway Administrations’ (FHWA) Traffic Noise Model (TNM) is used to predict traffic noise impacts. If the predicted noise levels approach or exceed FHWA’s noise abatement criteria, noise abatement measures are considered. Abatement measures such as noise walls or berms are effective in reducing traffic noise that will result from the transportation improvement. While landscaping can be used as an effective visual barrier, studies have shown that trees and shrubbery alone do not provide significant reduction in noise levels and are not approved as a noise abatement measure.

To aid in the understanding of the nature of noise in general, and traffic noise in particular, the traffic noise tutorial was updated based on IDOT's new noise policy, approved in 2011. This information is presented in three parts, or modules, along with a section on frequently asked questions and a glossary of terms and acronyms. The first module explains what noise is, the way in which it is perceived and measured, variations within distances and how mobile sources affect noise. The second part of the tutorial presents information regarding the initiation of a noise analysis, federal regulations regarding traffic noise, a description of noise monitoring and the components or inputs used in the TNM. Part three describes various noise abatement measures and approaches and describes noise barrier evaluation and design.

IDOT’s Highway Traffic Noise Assessment Manual describes techniques and procedures for analyzing and reporting traffic noise impacts. The Manual was updated in 2011 based on IDOT's new noise policy, and includes a discussion of abatement measures which can be incorporated into project designs to mitigate traffic noise impacts. Also included are references and examples to aid in the evaluation of traffic noise and abatement, as well as guidelines for the documentation of analyses in IDOT environmental documents. This guidance manual is issued in an effort to ensure that studies and reports on traffic noise prepared by or for the Department are consistent with existing laws and regulations and are technically accurate and sufficient.

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