As sound barriers generally reduce volumes by 5 to 8 dBA, their use is usually not as effective in less noisy areas. A 10 dBA increase is judged by most people as a doubling of the loudness of sounds. Noise abatement will generally not be considered for heavy maintenance, rehabilitation projects and existing conditions. After it has been determined to consider noise abatement as outlined above, several factors must be examined to determine if construction of sound barriers is feasible and reasonable. These factors include benefits to those impacted by noise, the cost of abatement, and overall social, economic and environmental effects of sound barrier construction.
Feasibility deals primarily with design and engineering considerations.
Unless special conditions exist and effective abatement can be provided, it is not considered feasible to provide noise abatement on non-controlled or partial access control highways. Reasonableness is a more subjective measure. This consideration should show that good judgement and common sense were used in making a decision. 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.