The first results are in since 700 test noise reduction panels were installed on south end of the I-5 Ship Canal Bridge and they show noise is down in some areas but not a majority.
The $7 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.
According to a WDOT e-mail, acoustic tests were done at 18 locations on both sides of the project area: next to the panels, under the panels and two or three blocks away. Measurements were done at the same level as buildings and below freeway lanes.
Testers also spoke to neighbors about what effect they had noticed.
According to the WSDOT e-mail, "the panels are working as well as predicted in about a third of the locations, but not as well as predicted in about two-thirds of the locations."
The best reduction (down three decibels) was on the west side of the bridge just past where Franklin Ave. E. deadends. A two decibel reduction was noted, also on the west side. Readings that showed no noise reduction came mostly from the east side of the test area. You can see the readings and their locations on this WSDOT map.
According to the WSDOT project website, a three decibel change is "noticable" and a five decibel change is "considerably noticable." For comparison, typical conversation speech rates about 60 decibels.
Measurements are done at ear level (about 5 feet off the ground) and atmospheric conditions, time of day and traffic mix are noted. Readings will continue to be done each quarter for the next three years. A final report is expected in November 2013.
If you have questions or comments about the project, contact the WSDOT's Tim Sexton at firstname.lastname@example.org or 206-440-4549. More information can be found on the projects website.
To see Eastlake Ave.'s video on the project, go to this previous post.