Evaluation of Alternatives to Sound Barrier Walls

The existing Indiana Department of Transportation's (INDOT’s) noise wall specification was developed primarily on the basis of knowledge of the conventional precast concrete panel systems. Currently, the constructed cost of conventional noise walls is approximately $2 million per linear mile. The noise wall is considered to be cost effective when a 5 dBA reduction can be achieved at a cost of no more than $25,000 per benefited receiver or $30,000 per benefited receiver in those cases where a majority of the receivers were in place prior to construction of the highway. In many areas, however, the above cost-effectiveness criteria are exceeded with the result that the areas are not eligible for federal-aid funding for noise abatement. Consequently, the residents in these areas are dissatisfied that no noise reduction measures are provided to them. Several alternative options may be considered by INDOT to address the above issues. The first option would be to raise the cost per receiver to make more areas eligible for noise walls. The second option would be to do nothing. The third option would be to adopt an optional line of sight (LOS) wall policy to improve customer satisfaction at a less expensive cost. Critical review was conducted on the current traffic noise policies by state departments of transportation (DOTs) nationwide, including Type II project participation, reasonableness of noise abatement, cost effectiveness of noise abatement, and third party funding. Four different types of noise barriers, including one conventional precast concrete wall and three LOS walls were installed in the study areas for field investigation. Evaluation was made on the issues relating to the construction, cost and structures of the installed noise walls, particularly the LOS walls. Pre- and post-installation noise measurements were made in the field to determine the noise reductions of the installed noise walls. Psychoacoustic-based approach was utilized to further evaluate compare the field acoustic performance of these four noise walls. Federal Highway Administration (FHWA) traffic noise model (TNM) 2.5 was also employed to predict the noise level in the design year and address the sensitivity issues associated with traffic volume, vehicle speed, noise wall height, noise wall length, and noise reduction coefficient of noise wall. Furthermore, community noise surveys were conducted before and after the installation of noise walls to identify public perception of the LOS wall performance and public involvement in noise abatement. Main findings and recommendations were made to modify INDOT traffic noise policy and noise wall specifications.