The Indiana Department of Transportation is comparing four driving surface techniques as it reconfigures and repaves the intersection of interstates 465 and 65 southeast of Indianapolis. One method in particular, researched at Purdue University, may decrease road noise to the extent that such barriers as those shown in red above may be less necessary on future highway projects. INDOT
The FHWA has awarded a $2-million innovative technology grant for a project in Indianapolis that will use a concrete finishing technique designed to improve grip while reducing noise.
August 13, 2013—The Indiana Department of Transportation (INDOT) recently received a $2-million grant from the Federal Highway Administration (FHWA) to test a new concrete finish on a portion of a project to improve the intersection of I-465/I-65 in southeast Indianapolis.
The multifaceted project, known as Operation Indy Commute, includes a new two-lane flyover connecting I-465 west to I-65 south, a new alignment of the I-465 east to I-65 south ramp to accommodate the flyover, and several lane additions and road improvements aimed at reducing traffic congestion in the area.
On a two-mile section with auxiliary lanes, INDOT will test four different concrete finishing treatments, including one that research by Purdue University indicates will decrease road noise by 10 decibels while increasing road grip.
“This technology is a different means of constructing pavement,” says Mark Miller, P.E., INDOT’s director of construction management. “Traditionally, Indiana has tined concrete surfaces to create transverse lines across the pavement.” This creates a channel to collect water and move it off the road surface quickly.
In the new process, once the concrete has hardened, workers will make a fine pass over the surface with a milling machine, leaving a smooth surface. This process is called diamond grinding. A second pass will be made with a machine fitted with blades to cut 1/8 in. wide longitudinal grooves in the surface. Research indicates that such grooves are equally effective at removing water as transverse tines.
“We use milling machines all the time on pavement,” Miller says. “What’s different with this machine is the type of blades—the diamond blades. You achieve a very smooth surface and nice, straight longitudinal grooves in the pavement.”
This contrasts with attempts to longitudinally tine road surfaces. Because it is exceptionally difficult to maintain perfectly straight longitudinal tines, the geometric differences have a tendency to cause car and motorcycle tires to track the grooves and their irregularities. This can prompt motorist complaints.
“This technology is different,” Miller says. “You really won’t feel it. But it’s definitely much quieter pavement.” Research indicates that this type of surface—which carries an approximately 10 percent price premium over traditional tining—actually improves road grip.
“With your traditional tining, you have a very rough surface texture. When you drag that tine through the concrete, you pull up pieces of aggregate and mortar. You get a rough surface. When we use a diamond grinder, you are going to have more tire contact on the surface,” Miller says.
The test builds on research by Purdue University, which identified the interface of tires with the road surface as the primary source of highway noise and investigated variations in road surfaces as a means to reduce noise levels.
Noise levels have been a concern on this project, which will include more than $8 million in noise barriers, according to a noise impact analysis prepared for INDOT. The surfaces being tested by INDOT in the project might eventually lead to a reduced need for noise barriers on future projects, Miller says.
“We would like to see eventually if this could reduce the need for noise barriers. That’s quite possible,” Miller says. “If it could, you could definitely justify the increased premium costs for the pavement. Part of the reason for this research is to get some feel from the contractors if we could develop efficiencies if we used it more often. And see if it is worth the extra premium in initial costs.”
The other three sections in the test will involve more customary techniques. One section features traditional INDOT tining. Another section will feature longitudinal tining with technical specifications from the Iowa Department of Transportation. The final method will be transverse tining with modified spacing between the tines.
“We were trying to find a project [in which] we could try all three and compare them,” Miller says. “With the length of this project, it seemed to be the appropriate project.”