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Since barrier wall B1 at a height of 20’ meets the SCDOT reasonableness criteria for cost-effectiveness based on the $35/square foot prescribed cost, evaluation continues.

The next step was to complete a project-specific cost estimate for barrier wall B1. As a reminder, SCDOT’s Noise Abatement Policy states that “During the detailed noise abatement evaluation, a more project-specific construction cost should be applied at a cost per square foot basis.”

The Charleston lowcountry area has stringent design requirements due to our geographical susceptibility to earthquakes and hurricanes. This results in costly structural foundations for the noise wall. In addition, the noise wall would cross an existing stream so construction would impact wetlands and require culvert pipe extensions. These project-specific factors are not taken into consideration with the $35 per square foot prescribed cost that is used in the initial cost-effectiveness evaluations. See Page 33 (Appendix C) of the Northwoods Estates Noise Impact Assessment for the project-specific cost estimate that was prepared for barrier wall B1.

The detailed project-specific cost estimate for barrier wall B1 resulted in a cost of $67.05/square foot, with cost per benefited receptor estimated at $57,268. This estimate exceeds the $30,000 allowable cost per benefitted receptor; therefore, the evaluation stops and the barrier wall is considered not reasonable to construct.