The height above ground level facing the receptor should not exceed a maximum of 7.5 meters, or approximately 25 feet. Barrier scale - It generally will not be considered reasonable to construct a barrier unless the receptor is located a horizontal distance at least four times the wall height from the proposed barrier. Sound barriers can have an overwhelming visual impact on receptors located closer to the wall. It generally is not considered reasonable to provide abatement if the difference between existing and design year noise levels is 3 dBA or less, as this is considered a barely perceptible change. Unless special conditions exist, it generally is not considered reasonable to provide abatement for impacted businesses.
Businesses usually prefer visibility from the highway rather than noise abatement.
Unless special conditions exist, it generally is not considered reasonable to provide noise abatement for isolated receptors. The cost of abatement versus the noise reduction benefits is usually excessive. Clear recovery zone - A noise barrier will be located behind the vehicle clear recovery zone or incorporated into a safety device such as a Jersey barrier. The factors listed above are not intended to be all encompassing. Rather, these are to illustrate some of the factors that should be considered in determining the feasibility and reasonableness of proposed abatement measures.