Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/412488
Better Roads November 2014 7 RoadScience by Tom Kuennen, Contributing Editor N oise emissions are as much of an environmental problem for urban traffi cways as exhaust pollu- tion, but new research is showing how sound wall performance can be improved, and how traffi c noise can be mitigated. Decades of research have shown that blendings of noise wall, the right choice of vegetation, and low-noise pave- ments such as the Next Generation Concrete Surface (NGCS), or asphalt open-graded friction courses (OGFCs), will suppress traffi c noise much better than any one of those elements by itself. Sound barriers are of different compositions, including metal, wood and recycled plastic fabricated to resemble wood, but precast concrete is by far the preferred material, as it's durable and can be cast into any kind of aesthetic form, including locally signifi cant iconography. But the costs of sound walls vary widely, and they're al- ways expensive, ranging from $2 million per linear mile in Indiana (2014), to an average of $3.9 million per mile, ac- cording to 2009 estimates by the Washington State Depart- ment of Transportation , with lower costs for rural barriers, and higher for urban. The cost – versus the number of entities to benefi t – is a factor in whether they are constructed at all. Last year's National Cooperative Highway Research Council Report 738: Evaluating Pavement Strategies and Barriers for Noise Mitigation at- tempts to reconcile today's "quiet pavements" with the cur- rent federal law, which doesn't take them into consideration when mitigating traffi c noise. "Title 23, Part 772, of the Code of Federal Regulations re- quires that noise analysis be performed for specifi c types of projects when potentially impacted receptors are present," NCHRP 738 says. "This regulation identifi es several noise mitigation measures but excludes pavements as a noise abatement measure. Recent advances in quiet pavement technology have shown the potential for using such abate- ment technology as an alternative to noise barriers. How- ever, issues such as cost, maintenance requirements, and the ability to maintain noise reduction features throughout time Sound walls are only one element of the next generation of noise reduction for urban freeways and traffi cways. Sound (Wall) Advice Photo courtesy of Tom Kuennen Sound walls are required for most Type I projects that meet the criteria