Latest I-5 noise reduction panel readings: No change from first round

UPDATE: This post has been updated since it was first published. A link to the WSDOT results has been added.

The latest results from the I-5 Ship Canal noise panel test are in and they don’t look much different from the first test which found a reduction in traffic noise but not as much as expected.

Results for the February tests, according to an e-mail from the Washington State Department of Transportation, show “virtually no change from the first round of post-construction readings in October, 2010, but some measurable decrease compared to pre-construction in April 2010 when there were no panels at all.”

You can see maps and a table of the February results here.


The October readings found the panels were reducing noise as expected in only about a third of the locations monitored. In two-thirds of the locations the results were less than expected with reductions of zero to three decibels. The goal was a four to five decibel reduction. Humans can detect a three decibel drop in noise.

The February results again show reductions of zero to three decibels. In two locations along Harvard Avenue E. readings actually went up one decibel from the pre-construction levels. The WSDOT website says these results are “not unexpected.”

Noise was sampled at 18 locations around the southern end of the Ship Canal Bridge.

The $5.9 million study began in 2005. The Washington State Department of Transportation is testing what effect large flexible panels hung under the top deck of the Ship Canal Bridge would have on reflected traffic noise. The project is also testing how durable the panels would be.

The WSDOT will make two more tests this year and then do an annual test in 2012. The Legislature allocated money from the 2005 gas tax for this project to “learn more about how reflected noise behaves in a complex urban environment and in double-decked structures,” according to the WSDOT’s e-mail.