UPDATED: September 2011
Are the panels performing as you expected them to?
The panels are not performing as well as we expected them to. The panels are reducing some noise (1-3 decibels), but not as much noise as the models predicted (4-5 decibels). Three decibels is considered noticeable to the human ear.
The noise models replicated the reflected noise from the express lane ceilings, but did not take into account other sources of noise like street noise from Harvard Avenue or Allison Street and refracted noise that bounces off the bottom edge of the noise panels. When our acoustics engineers go into the field, they can’t eliminate these other sources of noise in a real setting so it’s difficult to measure the success of the noise panels on the express lanes.
While noise is noise to anyone who lives near the express lanes, isolating and addressing certain kinds of noise is the scientific and best practice to approach noise reduction.
What are neighbors reporting?
Residents who have a line of sight to the ceiling of the express lanes are reporting very little if any change in noise levels. This is consistent with the theory that reflected noise – the noise that bounces right off the ceilings and into nearby homes - is the loudest. Residents who live a block away and have no line of sight to the express lane ceiling report a noticeable reduction in noise.
What’s working?
The panels are working. Their quilted texture is absorbing the reflected sound waves generated by car wheels on the pavement.
What’s next?
WSDOT acoustics experts have completed four quarters of testing and now will test only once a year. A final report is due to the Legislature in 2013.
Between now and then, engineers will review the data they do have to learn more about noise and how it travels in this unique environment.
What is WSDOT testing?
We are testing a noise-reducing technology that is made of a lightweight material - in this case, quilted vinyl panels. This type of material is typically installed on ceilings to absorb noise in a variety of environments, including classrooms and theaters. Since a ceiling treatment like this is not typically used on transportation structures, we installed a test section on the ceiling above the lower deck of the I-5 Ship Canal Bridge and will monitor it for three years to evaluate its effectiveness in reducing noise.
The 500-foot test section consists of approximately 700 4-foot by 8-foot panels attached to the south end of the express lane ceiling. Seven rows of panels on each side. The Ship Canal Bridge provides an opportunity for us to investigate innovate ways to reduce noise when faced with several challenges including noise on a double-deck structure, noise moving over water, and reflective noise.
WSDOT worked with noise experts to develop the pilot study and come up with a configuration of panels that would best address the noise challenges. This study will provide an opportunity to validate the computer models and determine the true effectiveness of the noise panels in this environment.
How much do the panels cost?
The construction cost to install the panels in $2.3 million. The overall budget to look at noise on I-5 in the vicinity of the Ship Canal Bridge was $7 million, funded through the 2005 gas tax.
Where is the test section on the bridge?
The test section is on the south end of the Ship Canal Bridge The test section is approximately 500 feet long and is located between E. Gwinn Place and E. Allison Street.
How does WSDOT decide which areas receive funding for noise reduction projects?
WSDOT identifies sites where noise is a concern along highways, including in neighborhoods established before the freeway was constructed, and prioritizes them according to multiple characteristics. This information is provided to the Legislature. It is up to the Legislature to decide which areas to fund and the amount to allocate to funded projects.
Why are we evaluating noise reduction methods on the bridge?
Highway traffic noise can interfere with sleep, work and other daily activities during the day and night, and is a concern for many residents living along state highways. The I-5 Ship Canal Bridge is one of several projects where we are working to learn more about how to reduce noise in challenging environments. Knowing that people live next to highways and will always live next to highways, we want to learn more about noise in these urban environments so we can develop reduction strategies that are realistic, cost-effective and feasible. This particular area is ideal to test some theories about noise.
This test site on the Ship Canal Bridge is located in a heavily traveled urban area and traffic noise from the bridge reaches the densely populated Seattle neighborhoods of Eastlake, Roanoke Park, University District and Wallingford. Due to the large number of affected residents, high noise levels, and the close proximity of communities to the highway, we identified the area near the I-5 Ship Canal Bridge as one of the top ten priorities in the state for reducing traffic noise.
How much noise is coming from the bridge?
Existing noise levels in the neighborhoods surrounding the bridge range from 66 to 87 decibels. For comparison, a train passing by at 50 feet away is approximately 70 decibels and a jackhammer at 50 feet is approximately 90 decibels. Above 66 decibels, it is difficult for two people standing three feet apart to hold a conversation.
Who will benefit from this test?
Estimated noise reduction will vary depending on the proximity of residences to the bridge. Residents closest to the noise-reducing treatment will experience the greatest benefit. Those farther from the bridge will receive less benefit. What we learn from this test may be applied to other areas and benefit others.
Other than this study, what else has WSDOT done to reduce noise?
In response to community input, we currently close the I-5 express lanes on the bridge from 11 p.m. to 5 a.m. on weekdays and 11 p.m. to 7 a.m. on weekends. This reduces the amount of highway traffic noise residents near the bridge experience during the night.
Understanding that noise is a significant issue for residents throughout the state, WSDOT continues to develop strategies to reduce noise:
We build concrete noise walls.
We are currently conducting a pilot study of non-concrete light-weight noise walls that may provide cost and constructability benefits.
Why don’t you just build noise walls instead of testing a new technology?
We use noise walls where it’s cost-effective and where we are likely to meet our noise reduction goals. Noise walls would be difficult to build on the Ship Canal Bridge because the entire structure would have to be retrofitted to handle the weight of concrete noise walls.
How did you select the south end for the test section?
The results of our structural analysis show that we would need to modify the north end and steel truss portions of the bridge in order to accommodate the panels, while the south concrete section would not require any modifications.
What sort of safety measures are in place to make sure the panels don't fall down?
We have been working with structural engineers, the Bridge and Preservation Office and the WSDOT maintenance team on the design for the ceiling treatment test section. This group of experts has helped us develop a plan that includes redundant safety mechanisms which include tying the panels together laterally and transversely to prevent the panels from detaching from each other, the ceiling or moving during high winds.
How will WSDOT determine if the noise-absorptive ceiling treatment is effective?
WSDOT noise experts are methodical in their approach to noise measurement. They have already taken “pre-construction” noise readings to develop a base line. After the work is completed, they will take more measurements and compare the before and after. To measure the long-term effectiveness of the noise panels, after construction, the noise experts will take quarterly measurements for the first year and annual measurements for the next two years. All information will be published to our web site.
We will also monitor the wear and tear of the panels over time and evaluate its maintenance requirements and qualities. This monitoring will help us understand how the noise-absorptive material works and determine if it should be used in future projects.
What happens if the test section doesn’t work?
We are measuring the noise reduction and the product’s durability. The monitoring will last up to three years and will help us understand how the noise-absorptive material works and determine if it should be used in future projects. The results of the monitoring will allow us to develop recommendations, which we will document in a final report. Since it is a test section, the ceiling panel installation is being designed to be temporary. The test section may be removed at some point in the future.
What will you do with the results of the test?
The results from the test section will help us learn more about noise and innovative reduction strategies. It will allow us to determine if these types of noise panels could be used on other transportation structures in other areas.
What other noise reduction technologies could be pursued if more funding becomes available in the future?
Other technologies that could be pursued if we had additional funding include:
- Installing a ceiling treatment on other portions of the bridge to address the reflected and reverberant noise from the bridge—this would be contingent on the results of the test section.
- Modifying the existing barriers on the bridge to add noise reduction capabilities to structures already in place.
- Constructing new noise walls at ground level in the area near the bridge approaches.
These options were not pursued in the initial phase of the study because they would require additional funding and/or structural modifications to the bridge.
How can I provide comments regarding this study?
You can provide your comments or sign up for study updates by contacting us:
E-mail: nwnoisewalls@wsdot.wa.gov