Noise can be defined as unwanted or unpleasant sound. All sound is produced by vibrating objects and transmitted by pressure waves in a compressible medium such as air. Sound waves are often characterized in terms of amplitude (strength of the wave) and frequency (speed of their variation) (Snyder 2006). Sound pressure or sound intensity levels are used to quantify the loudness of an ambient sound. The frequencies of sound audible to humans range from 20 to 20,000 Hz, and sound pressures range from 20 micropascals (Pa), the threshold of hearing, to 120 pascals (Pa), the threshold of pain (Norton 1989).
Human perception of changes in sound energy is also non-linear. Most observers perceive an increase or decrease of 10 dB in the sound pressure level as doubling or halving of the sound (FHWA 2011b). Noise levels are also affected by the distance from the source, with near-ground sources spreading out over a hemispherical volume. Noise wave energy is conserved with the result that sound intensity variation is proportional to the square of the distance from the source as it is spread over a wider surface. Therefore, the sound intensity level is decreased by a factor of four when the distance from the source is doubled.
Noise pollution has become an increasing concern in the U.S. and worldwide. Highway noise affects people in adjacent residences and businesses as well as people in vehicles; road noise effects on wildlife have also been identified (Clevenger et al. 2002). Various health and quality of life effects on humans from noise pollution have been identified by the World Health Organization (WHO 2013). Although somewhat controversial, attempts have been made to calculate the economic consequences of noise (Berglund, Lindvall, and Schvela 2000).
The FHWA states that effective control of undesirable highway traffic noise requires a three-part approach: noise compatible planning, source control, and highway project noise mitigation (FHWA 2013). If the highway agency identifies impacts, it must consider abatement and must incorporate all feasible and reasonable noise abatement measures into the project design. FHWA cannot approve the plans and specifications for a federal-aid highway project unless the project includes adequate noise abatement measures to comply with the standards (FHWA 2013).
Highway noise generated by passing vehicles comes from three sources: air passing over and around the vehicle (aerodynamic noise); the operation of the engine, exhaust, and drive train system (propulsion noise); and several mechanisms occurring as the tire passes over the pavement (tire-pavement noise) (Nelson and Phillips 1997; Sandberg 2001). As shown in figure 1, for passenger cars the tire-pavement noise dominates over propulsion noise at speeds above 20 to 30 mi/hr (30 to 50 km/hr), while at lower speeds the propulsion predominates. For heavy-duty trucks, it was found that propulsion noise dominates during acceleration from 0 to 50 mi/hr (0 to 80 km/hr), but tire-pavement noise dominates for all driving conditions above 50 mi/hr (80 km/hr) (Rasmussen et al. 2008). Tire-pavement noise depends on pavement surface characteristics, vehicle speed, environmental conditions, type of tire, and the dynamics of the rolling process (McDaniel and Thornton 2005). The tire-pavement noise level increases logarithmically with increasing speed (Sandberg 2001).
Figure 1. Estimate of light vehicle noise due to tire-pavement noise, powertrain noise, and aerodynamic noise at cruise speed (Rasmussen et al. 2008).
Two test methods have been developed that permit continuous noise measurements along a roadway at highway speeds and also focus on the tire-pavement noise alone (which can be addressed through pavement design and management). The first method is called the Close Proximity method (CPX), which uses the equipment shown in figure 2. The CPX method involves the use of directional microphones inside of an acoustically insulated enclosed space built on a trailer that is towed behind the vehicle. This device is primarily used in Europe.
Figure 2. Close Proximity (CPX) test trailer (Bendtsen and Thomsen 2008).
The second method is called the On-Board Sound Intensity (OBSI) method, and is illustrated in figure 3. This method was developed in the U.S. based on technology originally developed by General Motors Corporation and recently introduced into the pavement community (Donavan and Lodico 2009). OBSI measurement involves the use of directional microphones placed at the leading and trailing edges of the tire-pavement contact patch, just above the pavement, and is performed in accordance with AASHTO TP-76-09. Comparisons between the OBSI and CPX methods have been performed, and show that they have similar sensitivity to pavement characteristics (Donavan 2006). The OBSI is primarily used in the U.S. because the equipment is mounted on the vehicle and it does not require the use of a trailer as does the CPX method.
Figure 3. On-Board Sound Intensity (OBSI) setup (photo courtesy of John Harvey).
Practices that are available to pavement managers, designers, and specification developers that might be used to address tire-pavement noise are summarized in table 1.
|Tire-Pavement Noise Objective||Tire-Pavement Noise Improving Strategy||Economic Impact||Environmental Impact||Societal Impact|
|Reduce Noise on New and Existing Asphalt Pavements||Use durable open-graded, rubberized asphalt, or SMA mixtures||Open-graded mixtures generally have shorter lives than dense graded mixtures. SMA mixtures are more expensive than dense graded. Life-cycle cost analysis can be performed.||Quieter pavement benefit. Trade-offs depend on surface mixture impact and longevity. Can be calculated with LCA.||Quieter pavement improves the livability of neighborhoods near highways. Can potentially reduce stress on wildlife.|
|Reduce Noise on New Concrete Pavement||Eliminate transverse tining by using longitudinal textures; use quieter textures; use narrow (single-saw cut width) joints with recessed sealant if sealant is used.||Depends on alternative texture used. Generally very small cost compared to construction cost.||Quieter pavement benefit. Trade-offs depend on surface texture and longevity. Texturing generally low impact. Can be calculated with LCA.||Quieter pavement improves the livability of neighborhoods near highways. Can potentially reduce stress on wildlife. Must have adequate surface friction.|
|Reduce Noise on Existing Concrete Pavement||Retexture with conventional diamond grinding or NGCS||Relatively low cost treatment that also improves smoothness and removes faulting. Increased cost compared to Do Nothing.||Quieter pavement benefit. Trade-offs depend on surface texture and longevity. Texturing generally low impact. Can be calculated with LCA.||Quieter pavement improves the livability of neighborhoods near highways. Can potentially reduce stress on wildlife. Must have adequate surface friction.|
|Minimize Noise on Existing Pavement||Perform pavement preservation to minimize cracking, faulting and other surface imperfections that contribute to noise; use good practice for sealing to prevent overbanding||Can also reduce life-cycle cost||Quieter pavement benefit. Impact depends on traffic and interaction of smoothness and vehicle use. Can be calculated with LCA.||Quieter pavement improves the livability of neighborhoods near highways. Can potentially reduce stress on wildlife. Must have adequate surface friction.|
Bendtsen, H. and N. Thomsen. 2008. Surface Dressings - Noise Measurements Report. Technical Note 68. Danish Road Institute, Denmark.
Berglund. B., T. Lindvall, and D. H. Schwela (eds). 2000. Guidelines for Community Noise. World Health Organization, Geneva, Switzerland.
Clevenger, A., R. Forman, D. Sperling, J. Bissonette, C. Cutshall, and V. Dale. 2002. Road Ecology: Science and Solutions. Island Press, Washington, DC.
Donavan, P. 2006. Comparative Measurements of Tire/Pavement Noise in Europe and the United States - NITE Study (.pdf). FHWA/CA/MI-2006/09. California Department of Transportation, Sacramento, CA.
Donavan, P. and D. M. Lodico. 2009. Measuring Tire-Pavement Noise at the Source. NCHRP Report 630. Transportation Research Board, Washington, DC.
Federal Highway Administration (FHWA). 2011b. Highway Traffic Noise: Analysis and Abatement Guidance. FHWA-HEP-10-025. Federal Highway Administration, Washington, DC. (Web Link (.pdf)).
Federal Highway Administration (FHWA). 2013. Highway Traffic Noise Website (.pdf). Federal Highway Administration, Washington, DC.
McDaniel, R. S. and W. D. Thornton. 2005. "Field Evaluation of a Porous Friction Course for Noise Control." 84th Annual TRB Meeting Compendium of Papers. Transportation Research Board, Washington, DC.
Nelson, P. M. and S. M. Phillips. 1997. Quieter Road Surfaces. TRL Annual Review. Transportation Research Laboratories, UK.
Norton. M. P. 1989. Fundamentals of Noise and Vibration Analysis for Engineers. Cambridge University Press, Cambridge, England.
Rasmussen, R. O., R. J. Bernhard, U. Sandberg, and E. P. Mun. 2008. The Little Book of Quieter Pavements. FHWA-IF-08-004. Federal Highway Administration, Washington, DC.
Sandberg, U. 2001. "Tyre/Road Noise Myths and Realities." INTER-NOISE and NOISE-CON Congress and Conference Proceedings. Hague, Netherlands.
Snyder, M. B. 2006. Pavement Surface Characteristics: A Synthesis and Guide. EB235P. American Concrete Pavement Association, Skokie, IL.
World Health Organization (WHO). 2013. Noise and Health. World Health Organization, Regional Office for Europe, Copenhagen, Denmark.