SUMMARY
Forty-four States and the Commonwealth of Puerto Rico have constructed highway traffic noise barriers; six States and the District of Columbia have not. The most notable trend in highway traffic noise barrier construction is that SDOTs spend more than $100 million of highway program funds annually for this form of noise abatement. Starting in 1992, SDOTs have averaged spending more than $139 million per year. Since the first highway traffic noise barrier was constructed, sixty-five percent (65%) of all spending has been for Type I projects, and twenty-nine percent (29%) for Type II projects.
Most barriers have been made from concrete or masonry block, range from 9-17 feet in height, and average $16-21 per square foot in cost.
http://www.fhwa.dot.gov/environment/noise/barrier/tintro.htm
Note: Keep in mind the cost per foot above is not linear cost, while the cost per foot quoted above is linear cost.
To put this in other terms, each state is spending the equivalent of 33 miles of wall cost each year. If the states stopped for one year and contributed their noise budget for this wall, we could have the funds to do over 1,500 miles.