Researchers Open Eyes, Ears to Search for Quieter Roads

Traffic noise has long been a complaint of those living near highways. An answer to the problem may be within reach with the work being performed by engineers at Purdue University who last year formed the first center in the nation dedicated to understanding the precise physics behind highway noise.

“Our objective is to understand the fundamentals of highway noise, primarily the noise from the interaction of the tires with the road surface,” said Bob Bernhard, director of the Institute of Safe, Quiet and Durable Highways at Purdue University, West Lafayette, IN. “We’re studying both pieces, the tires and road surface.”

Europe has already demonstrated success in making highways quieter and some of that information can translate to the United States. However, the cost of the process used in Europe is a negative to work here, Bernhard said. And environmental factors on roads in areas that experience thaw and freezing weather also may have unique needs

“European researchers have hypothesized the mechanisms of noise generation and built quiet, porous road surfaces,” Bernhard said. “These hypotheses haven’t been proved, and that’s what we are going to go after.

“The additional challenge is to keep tires and roads safe, durable and affordable at the same time,” he said.

Engineers suspect that several mechanisms are to blame for road noise, including:

• Air that is trapped and compressed between a tire’s tread pattern and the road surface eventually bursts from the confining spaces, causing pops and whistles.

• The block-like shapes in the tread design smack against the road surface, like numerous tiny hammers.

• Those tread blocks and the underlying belts vibrate and radiate energy outward, producing sound much like the vibrating cones in stereo speakers.

Researchers will study these hypothesis, along with others to determine the cause of highway noise.

Research will include the use of lasers and sound waves to analyze noise-producing mechanisms in rotating tires. Engineers will study porous pavements that have been used in Europe to build quieter roads.

One of the studies will look at novel texturing schemes for concrete pavement. Currently “tining” is performed on concrete to increase friction, but it makes for a whining noise on the roadway. Research will look at other possible ways of texturing the surface to keep the friction and reduce the noise. Included in this will be research on creating porous concrete, similar to the porous asphalt used today in Europe, Bernhard said.

That technology also will be researched in asphalt. According to Bernhard, it’s believed that the porous surface relieves noise generation, as well as absorbs the sound similar to foam.

There are seven research projects included in the program, which was launched last August as part of the institute that is funded by a $3.6-million grant from the U.S. Department of Transportation. The grant is a dollar- for-dollar matching grant. Those funds are coming from private sources, including associations from the automobile industry, tire industry and asphalt and concrete industries. These groups also serve as members of an advisory counsel to the Purdue faculty and students working on the project, along with members of state and federal Departments of Transportation. Bernhard said he hopes to have those in the construction industry join this panel.

The institute is a joint project of Purdue’s schools of civil and mechanical engineering in collaboration with researchers from the Pennsylvania Transportation Institute at Penn State University, where researchers will make a database of sound produced by transit buses in efforts to reduce bus-related noise pollution, he said.

Once the research is complete, then tests must be done and results measured and publicized with recommendations. That will likely take a total of five years, Bernhard said. Part of the requirement for the grant is technical transfer, or getting the technology used in real life and tracking that use, he said.

These findings from laboratory research will be also incorporated into civil and mechanical engineering classes at Purdue. The findings also will be transferred to the highway and tire industries through workshops and design guidelines.

It will expand later to include research dealing with other sources of transportation-related noise, such as truck engines, as well as issues involving highway safety and durability, Bernhard said.


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