WSDOT is evaluating new types of pavements that might reduce freeway noise at the source. These new pavements are:
- Rubber asphalt open-graded friction course (OGFC-AR)
- Polymer modified asphalt open-graded friction course (OGFC-SBS)
- Concrete with new types of surface texturing
They have the potential to reduce noise coming from tires as they roll across the pavement surface. Test installations of the new types of open-graded friction course pavement are being evaluated on I-5 in Lynnwood, SR 520 near Medina and I-405 in Bellevue.
WSDOT Receives Award for Excellence in Quieter Pavement Research
The Quieter Pavement test sites on I-5, SR 520 and I-405 are three of the most tested and documented quieter pavements in the world. WSDOT received an award for excellence in Quieter Pavements Research from the Rubber Pavements Association (RPA) in recognition of WSDOT’s contribution to understanding the acoustics and performance of quieter pavements. RPA is a non-profit industry association of manufacturers, contractors, consultants, testing laboratories, suppliers, government organizations and individuals that encourage the use of asphalt pavements containing recycled tire rubber.
"Quieter Pavements" - not audibly quieter after six months
A sound must be more than 3 decibels quieter for most people to notice a difference. Both OGFC pavement types were at this level when they were built, but none of the sections are noticeably quieter now than the standard hot mix asphalt (HMA) pavement built at the same time. For additional details, view:
Concrete and Asphalt Pavement Test Locations
In addition to the evaluations of the open-graded friction course asphalt pavements mentioned above, WSDOT is also trying to make concrete pavements quieter. Different surface textures are being tried when new concrete pavements are being built and new methods of diamond grinding, including Next Generation Concrete Surface, are being used on existing concrete pavements. The map below shows the locations of all of the quieter pavement trial installations.
How are the test sections different?
All of the tested pavements are overlays and include sections of asphalt rubber binder and polymer modified binder. Each of the three test areas has one section of OGFC modified with rubber and one section modified with polymer. WSDOT built the test pavements alongside new conventional asphalt pavement to compare the noise characteristics and pavement performance accurately. The design for the OGFC pavements used at all three sites matched as chose as possible the design of pavements used in Arizona, one of the leading states using quieter pavements.
Traffic volumes on the test section of SR 520 are lower than the I-5 Lynnwood and I-405 test sections and have about half of the heavy trucks in the total vehicle mix (approximately 5% on SR 520). Another difference between the sections is that SR 520 and I-405 were paved during the day when temperatures were higher than during the nighttime paving of I-5. Finally, SR 520 and I-5 were installed on top of asphalt pavement, while the test sections on I-405 were installed on top of concrete pavement.
What are WSDOT and other states doing to reduce noise?
Historically, noise barriers have been the most effective method for reducing traffic noise. Noise barriers include noise walls and earthen berms that separate traffic noise from adjacent properties. Typical reduction is 5 to 10 decibels, with 10 decibels being about half the perceived noise level. While noise barriers can be effective, they can also be expensive to install and are not constructible or effective in all locations.
States like Arizona and California are using OGFC pavements to reduce noise levels on their urban roadways. In fact, the Arizona Department of Transportation (ADOT) provided WSDOT with the mix design for the OGFCs.
OGFCs are potentially quieter than conventional asphalt pavement because they are designed to have tiny air holes, or voids, throughout their entire depth. The air voids absorb and dissipate the sound generated by the tires on the pavement surface. The OGFC test sections also use a different binder than conventional asphalt. Each of WSDOT’s locations includes a section using asphalt rubber binder (OGFC-Rubber) and another using polymer modified binder (OGFC-Polymer).
Different surface texturing of concrete pavements can affect the noise performance, too. WSDOT is evaluating five types of new concrete surface textures for noise and durability:
- Next Generation Concrete Surfacing (NGCS) on Avondale Road in King County, on I-82 near Sunnyside
- Diamond grinding on I-5 in Seattle and on I-90 near Cle Elum
- Carpet drag on I-5 in Federal Way and on I-90 in Spokane
- Longitudinal tining on I-5 in Federal Way
What are quieter pavements?
The term "quieter pavements" has been applied to various flexible (asphalt) and rigid (concrete) pavements that apply one or more noise-reducing properties. In general, asphalt pavements tend to be quieter than concrete pavements and Open Graded Friction Course (OGFC) pavements, at least initially, can be the quietest. OGFC pavements are the most common type of asphalt pavement specifically designed to reduce noise, which is why WSDOT is evaluating them.
For concrete pavements, the quest for quietness has focused on the use of alternative methods of finishing the wet concrete using textures that produce less tire noise. In addition, a research effort sponsored by the concrete industry has developed a diamond grinding method for existing pavements that has produced the quietest concrete pavement ever measured. This new method, called Next Generation Concrete Surface (NGCS) is being evaluated at two sites in the state.
A host of factors influences the noise generated by tire and pavement interaction including:
- macro and micro texture
- tire tread configuration
- studded tire wear
- roadway surface openings (voids)
- joints in concrete pavements
- speed of traveling vehicles