Asphalt pavement mixes help reduce traffic noise at the point where the wheel meets the road. According to a National Cooperative Highway Research Program (NCHRP) report, quiet asphalt mixes can reduce the need for costly and unsightly sound barriers.1 And since low frequency noise, which can lead to greater driver fatigue,2 increases with roughness,3 smooth asphalt roads benefit not only those who live near a road, but also those who drive across it.
Crucial developments in asphalt technologies are key in helping to further reduce sound emanating from highways. In fact, research shows that developments like stone-matrix asphalt, open-graded friction courses, fine-graded surfaces and rubberized asphalt can help reduce highway noise by as much as 7 decibels.4 Reducing noise by just 3 decibels is equivalent to doubling the distance from the source of noise to the listener.
Different pavement designs can reduce noise in different ways. A porous or open-graded pavement can dissipate sound energy generated by contact between the tire and the surface; an even smoother surface, such as a fine-graded mix, has less macrotexture, reducing contact forces, and thus noise, between the pavement and the tire.5
Road noise can also influence drivers’ perception of the roughness (and thus serviceability), measured by the International Roughness Index (IRI), of a road. A Washington State Department of Transportation (DOT) analysis found that drivers perceived a noisier pavement as being rougher than a quieter pavement with a similar IRI value.6
The asphalt industry continues to research and develop pavements that are quiet for drivers, neighborhoods and businesses adjacent to busy roads.
In the spring of 2013, the Virginia Department of Transportation (DOT) found that the use of quiet asphalt technology was able to reduce tire-pavement noise by a readily noticeable 5 decibels.7 The study, commissioned by Virginia’s General Assembly, seeks to add specifications for quiet pavement technologies into contracts in cases where sound mitigation is a consideration.
In February of 2014, researchers from Purdue University developed a model for predicting the noise level of an asphalt pavement design for the Minnesota Department of Transportation (MnDOT). The model is able to predict the on-board sound intensity (OBSI) level of various asphalt surface mixes to within 1.5 decibels.8 This prediction model will help MnDOT estimate tire-pavement noise so that existing mix technology can be deployed as a noise reduction tool — minimizing noise at the source.
On-board microphones capture the noise differential as a vehicle transitions from an asphalt rubber surface (ARFC) to a portland cement concrete pavement (PCCP) and then back to smooth and quiet asphalt.
Noise pollution comes in many forms and can deeply affect communities — from social costs, including disrupted sleep9 and, in extreme cases, mental illness and cardiac disorders,10 to lower home values.11 Mitigating noise with sound barriers can be expensive and in some areas difficult to construct due to limited right of ways. For these reasons, road owners and the pavement industry are working to address traffic noise at the source with a smart, sound pavement choice — asphalt.
Donavan, P.R., L.M. Pierce, D.M. Lodico, J.L. Rochat, and H.S. Knauer (2013). NCHRP Report 738: Evaluating Pavement Strategies and Barriers for Noise Mitigation. Transportation Research Board of the National Academies, Washington D.C.
Landström, U., S. Lindblom-Häggqvist, and P. Löfstedt (1988). Low Frequency Noise in Lorries and Correlated Effects on Drivers. Journal of Low Frequency Noise and Vibration, Vol. 7, No. 3, pp. 104–109.
Shafizadeh, K., F. Mannering, and L. Pierce (2002). A Statistical Analysis of Factors Associated With Driver-Perceived Road Roughness on Urban Highways. Report WA-RD 538.1. Washington State Transportation Center, University of Washington, Seattle, Washington.
McDaniel, R.S., A. Shah, T. Dare, and R. Bernhard (2014). Hot Mix Asphalt Surface Characteristics Related to Ride, Texture, Friction, Noise and Durability. Report MN/RC 2014-07. Minnesota Department of Transportation, St. Paul, Minnesota.