Road Science Tutorial
Better Roads Staff
• Noise-Compatible Planning. Local governments should regulate land uses to restrict noise-sensitive uses adjacent to highways.
• Source Control. EPA noise regulations set the maximum noise level 50 feet from the centerline of travel at 80 A-weighted decibels.
• Highway Project Noise Mitigation. FHWA sets a five-step process for transportation agencies managing highway project planning and design to identify and abate highway noise impacts.
Download a summary of the new rules at environment.fhwa.dot.gov/strmlng/newsletters/sep10nl.pdf The complete final rule may be accessed at]edocket.access.gpo.gov/2010/2010-15848.htm
A recap of current federal and state initiatives in noise suppression – including a look at sound-absorbing noise walls – appears in the December 2010 ROAD SCIENCE (see Gaining Influence in 2011, December 2010, pp. 9-17).
Next-Generation Concrete Surface
This year, the concrete industry launched a portland cement concrete surface that will suppress noise from concrete pavements while enhancing friction and smoothness. A refinement of the pavement diamond-grinding process, the Next Generation Concrete Surface (NGCS) is being promoted by the International Grooving & Grinding Association and its allies, the American Concrete Pavement Association, Portland Cement Association and Purdue University.
When this innovative surface was used on an urban highway in Duluth, the response was overwhelming, IGGA reports. “Residents have called in asking how the roads became so quiet and it has even made the front page in the local newspapers,” says IGGA Executive Director John Roberts.
The best way to understand the difference in the sound level with NGCS is to experience it; a high-traffic freeway with 240 vehicles will now sound comparable to only 120 vehicles of traffic, a substantial reduction in sound, IGGA reports. This is a considerable decrease for areas with a greater need for quieter roads, such as urban or residential areas.
The NGCS is a diamond saw-cut surface designed to provide a consistent profile absent of positive or upward texture, resulting in a uniform land profile design with a predominantly negative texture. NGCS is a hybrid texture that resembles a combination of diamond grinding and longitudinal grooving.
The texture is most easily constructed in a two-pass operation using diamond-tipped saw blades mounted on conventional diamond-grinding and grooving equipment. Testing has shown that these textures can be used for both new construction and rehabilitation of existing surfaces.
The construction method has two separate operations, reports the Washington State DOT in its April 2011 report, Evaluation of Long-Term Pavement Performance and Noise Characteristics of the Next Generation Concrete Surface. The first operation creates a flush ground surface and eliminates the joint or crack faults while providing lateral drainage by maintaining a constant cross-slope between grinding extremities in each lane.
The second operation provides the longitudinal grooves, Washington DOT reports. The longitudinal grooves are 0.125 inches wide, and 0.125 to 0.375 inches deep. The longitudinal grooves are spaced approximately 0.5 inches center-to-center. The grooves are constructed parallel to the centerline.
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