Where the Rubber Quiets the Road

Creating mixtures for smoothness and low noise

By Lauren Heartsill Dowdle

Grinding, loud, uneven roads can leave drivers and their vehicles shaken up after a long ride. So it’s no surprise that road conditions are the public’s No. 1 criterion for satisfaction, according to a 2002 Federal Highway Administration (FHWA) survey.

“Noise can affect the passengers in a vehicle, as well as the people living and working along a road,” says Trenton Clark, director of engineering, Virginia Asphalt Association (VAA), in Richmond, Va. “The owner should keep that in mind when specifying a treatment for a roadway – either new construction or resurfacing. It is a balance between managing costs and benefits.”

And although a road project’s checklist might not include the end-user’s approval, smoothness standards and specifications continue to be an important part of many road builders’ contracts and planning stages.

“Several factors go into achieving a smooth ride: mix design, mix delivery to the project, proper paver operation and compaction,” Clark says.

But eliminating bumps is not the only, or main, benefit of laying an even surface – a National Cooperative Highway Research Program analysis shows improved smoothness extends pavement performance life by up to 50 percent.

“Transportation agencies have a goal to provide the lowest lifecycle cost for road treatment,” says Jim Barnat, vice president of innovation, Road Science, a division of ArrMaz. “As secondary considerations, these agencies look at aesthetics, ride quality and quietness characteristics. They generally focus on durable pavement structures and crack-resistant surfaces, providing the best return on their investment.”

On the road to create lasting, smooth surfaces, some have stopped to address noise concerns, as well. These departments of transportation, including those in Arizona, Florida, Minnesota and Kansas, have tested pavement alternatives by using rubberized-asphalt mixtures near residential and sound-sensitive areas to decrease the traffic noise.

“Road noise is generated from two main sources – a vehicle’s engine/drive train and the tire-pavement interaction,” Clark says.

Virginia roadbuilders conducted an experiment with various surface mixes and aggregate sizes with the goal of discovering which materials created quieter, yet smooth, roads.

The Experiment

When a bill was introduced in Virgina in 2011 to develop quiet-pavement technologies to aid in sound mitigation, the Virginia Department of Transportation (VDOT) constructed road demonstrations to test various surface mixtures.

VDOT and its asphalt industry partner, the VAA, created noise-reducing surface mixes to be used on the projects, with each site including a control section and three experimental sections.

“When rubber can be used to reduce the overall cost of the asphalt mix and provide equal or superior performance, then rubber should be used.” Trenton Clark, director of engineering, Virginia Asphalt Association (VAA)

The quiet pavement project on State Route 7 went to Superior Paving, and Branscome won the remaining two sites – one west of Williamsburg on State Road 199 and another on State Road 288.