Transparent barriers mitigate highway noise

In 2003, soon after construction along Interstate 30 near downtown Dallas was completed, Texas DOT (TxDOT) began getting complaints about traffic noise.

Agency managers spent the next decade trying to resolve the issue. The challenge wasn’t just to make the neighborhoods along the one-half-mile stretch of roadway quieter. Strongly opposed to living next to a “Berlin Wall,” residents also wanted to maintain their view of a nearby park.

Dual-purpose solution

The heart of the problem was that the existing 8-foot concrete barrier was too short to muffle the noise. It needed to be 18 feet.

Unfortunately, the barrier’s foundation couldn’t support the weight of additional concrete. Nor could TxDOT afford to tear down the barrier to build a taller one.

Managers tried repaving with a quiet pavement asphalt mix and attaching noise absorbing panels to the walls on the opposite side of the highway—with minimal success.

Then, Mark McIlheran, PE, a consulting engineer for construction materials supplier Armtec, suggested raising the wall’s height by attaching clear barriers.

Introduced to North America in 1995 by Evonik Cyro LLC of Parsippany, N.J., Acrylite Soundstop are performance-grade acrylic panels, usually 5mm or 20mm thick, that may be combined with structural framing elements for larger areas. The panels are custom-produced to the size required, up to 8 by 20 feet, are TL-4 crash-rated, warrantied for 30 years, and have an expected useful life of at least 50 years.

Armtec and Evonik have delivered almost 100 similar projects throughout North America. In approximately decreasing order based on volume, other states that use the product include California, Ohio, New Jersey, New York, Virginia, Florida, Tennessee, and Minnesota.

Next page: Turnkey solution

Turnkey solution

This project was the first of its kind for TxDOT.

Armtec designed, sourced, and supplied the turnkey system, including steel posts, anchors, gaskets, detailed drawings for submission and approval by the department—and the panels themselves. They’re attached inside steel I-beams that extend down the residential side of the pre-existing concrete wall and pinched tight to the inside surface of the post flange by a steel angle bolted through the post web.

“Not only did they reduce noise levels, they were transparent,” says TxDOT Noise Specialist George Reeves. “The combination of these benefits led us to use them on an experimental basis, something we wouldn’t have been comfortable doing without adequate documentation concerning long-term weather stability and talking with other states that have used them.”

Measurements conducted by the Center for Transportation Research (CTR) at the University of Texas in the neighborhood directly behind the new barriers show noise reduction of 5 to 7 decibels.

“The people I’ve spoken with are happy with the new walls,” says CTR Research Engineer Associate Manuel Trevino. “They also like that they can see through them.”

Designers seek to preserve views; structural engineers strive to ensure safety. Implementing a solution that does both was both cost-effective and good public relations for TxDOT. So good, in fact, the department is installing the barriers on a second project on U.S. 75 north of Dallas.

Nathan Binette manages the Transparent Soundwalls Division of Evonik Cyro LLC. E-mail soundstop-us@evonik.com.