Researchers at a university highway research institute are using a unique machine to determine the factors that cause road noise when a tire meets the pavement.
Purdue University's Institute for Safe, Quiet and Durable Highways has used the 38,000-pound, 12-foot-diameter Tire/Pavement Test Apparatus since July 2002 to measure the noise coefficients between tires and various types of pavement surfaces, according to Robert Bernhard, co-director of the institute and director of Purdue's Ray W. Herrick Laboratories.
``We received it in July 2001, but we had to finish the electronics and controls,'' Mr. Bernhard said of the Purdue-designed machine. ``We're using it all the time.''
The curved machine allows sections of pavement to be fitted together in a circle. Two tires are then rolled over the stationary surfaces at widely varying speeds, with microphones and sensors recording noise and other data.
Preliminary findings from the first round of tests were discussed earlier this year during the 89th Purdue Road School, an annual transportation conference. The earliest tests effectively eliminated the tire carcass as a dominant cause of road noise, but the institute has no current plans to carry the tire testing further to measure the noise-causing aspects of tread designs and compounds, according to Mr. Bernhard.
``We have a fairly full schedule for the next six to eight months,'' he said, adding that the Tire/Pavement Test Apparatus will be used solely for pavement testing during that time.
Currently the institute is studying the noise dampening properties of Portland cement concrete when given porous surfaces or blended with natural and synthetic fibers. In late summer or early fall, Mr. Bernhard said, researchers will start experimenting with asphalt with porous or ``open-ended' surfaces and blended with fibers and recycled materials.
Rubberized asphalt, however, will not be among the pavements tested. ``We don't have the funding to study it, but we'd like to,'' Mr. Bernhard said, adding that the Arizona Department of Transportation is conducting a three-year study of the noise mitigation potential of rubber asphalt concrete.
The institute has not tried to find a standardized tire for the Tire/Pavement Test Apparatus, according to Mr. Bernhard. ``We are using a production tire that the supplier had given to us for a previous study,'' he said. He did not identify the make of tire or its supplier.
The Institute for Safe, Quiet and Durable Highways began operations in 1999, a year after Purdue received a $1.4 million grant from the federal government to research the physics behind highway noise and find the best balance between quiet and durability in tires and road surfaces. It since has received about $1.8 million more from the university, various tire companies and the Indiana Department of Transportation, Mr. Bernhard said.
The federal grant was not renewed, but funding from other sources means the institute can count on funding of just under $500,000 annually, he added.
``We're downsizing a little bit, but we see opportunities in the future for other grants,'' he said. ``The future is uncertain, but we're very hopeful.''