Noise Barriers - Noise Analysis

Noise barriers

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Note: this video was produced for MnDOT&#;s Noise Policy and some provisions may not be relevant for all future road construction/noise wall projects. Please see MnDOT&#;s new Noise Requirements page for new provisions.

When does MnDOT conduct noise studies?

Two programs activate a noise analysis:

• The first is for a major reconstruction project in which the road would be expanded with additional lanes for more than a mile or would significantly change the alignment of the road. This type of project usually requires an in-depth environmental review process in which many issues are looked at one of which is noise and noise barriers.
• The other program is commonly referred to as a retro-fit project. It is for stand-alone noise walls where major reconstruction is not planned in the near future. As part of this program, areas are ranked by existing noise levels, length of barrier, and number of homes. View a copy of the ranking results.

How does MnDOT determine whether a noise barrier can be constructed?

A noise barrier must be both feasible and reasonable if it is to be constructed with a highway project. The reasonability of a noisewall is determined by factors such as cost, amount of reduction in noise, safety, and site features. Decisions on noise mitigation locations are determined on a case-by-case bases.

How do noise barriers work?

Noise barriers block the direct path of sound waves from the highway to homes and businesses along the highway. They do not eliminate noise, they only reduce the noise. To be considered effective, a noise barrier must reduce noise impact to receptors by at least 5 decibels.

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Can noise increase as it passes over the barrier?

No. Noise does not increase as it passes over the barrier. The further noise travels, the greater the reduction in noise.

Could trees be planted to block traffic noise?

There isn't enough space to plant the amount of and size of trees needed to reduce traffic noise. To effectively reduce traffic noise there needs to be room for at least 100 feet of dense evergreen trees that are 15 feet tall or more. Additionally, if trees are used to reduce traffic noise, they need to be maintained. MnDOT lacks the necessary resources to maintain trees or other vegetation.

Do noise barriers affect property values?

There haven't been any studies that link property values to noise barriers. Future buyers may either appreciate the noise reduction the barrier provides, or they may have aesthetic concerns about its presence.

Read other noise FAQs.

The objective of this study was to determine the actual and perceived effectiveness of noise barriers along interstate highways. Using a 5-mile section of Interstate 71 in the greater Cincinnati area as the study area, traffic noise readings and opinions of residents living along the sections of the highway were recorded. Noise readings were taken before and after the noise barriers were erected. A questionnaire was designed to elicit noise-related annoyance of the residents in the areas adjoining the highway. The results indicated that, in general, noise barriers were effective as indicated by a reduction in noise levels by as much as 11 dBA. The barriers, however, failed to bring noise levels for locations closer to the highway within the levels desired by the government (67 dBA). Most residents living right next to the highway were very satisfied with the installation of noise barriers. In general, these individuals felt that the quality of life improved with the noise barrier installation. The same, however, was not true of residents living a few blocks away from the highway--they felt the noise barriers were a waste of money. There was no significant difference in traffic noise pattern during the weekdays or weekends. Noise readings taken in two different locations were observed to be similar.

If you want to learn more, please visit our website Noise Barrier Panel.