Presuming acoustical requirements are met, selection is usually based on cost and aesthetics. Costs that must be considered include site preparation, the barrier material itself, foundations, fabrication, erection, and maintenance. Aesthetics should be judged with the involvement of personnel with diverse backgrounds, and public participation should be encouraged. However, there are numerous factors that go into the final selection. Some factors that should be considered in wall selection are summarized in Table 9.1.
The reasonableness of constructing a noise barrier can be judged from a cost-benefit analysis. For example, Minnesota uses the following procedure. The benefit is based on the summed insertion loss (noise reduction) for each residence in the first two rows
TABLE 9.1 Factors to be Considered in Noise Wall Selection
Site
Site geometry Right-of-way width Relation to source height Configuration, single or parallel
Noise source
Traffic type and volume Noise frequencies Extraneous noise sources Material
Structural integrity Durability and maintenance Susceptibility to vandalism Acoustical properties
Cost
Site preparation Wall material Foundations Fabrication Erection Maintenance Aesthetics
Scale relationship
Environmental relationship
Line form
Color
Texture
Community preferences
of homes nearest the noise wall where the insertion loss is greater than 5 dBA. The ratio of this sum in dBA to the cost of the barrier in thousands of dollars must be greater than 0.4 for the benefit to be considered reasonable.
