Noise from the tire/pavement interaction has significant effects. Besides being a nuisance to people, it can have measurable health and economic impacts. It may lead to impaired judgment, reduced efficiency and productivity, and sleep disruption for individual exposed to significant noise levels.
What is Quieter Pavement?
“Quieter pavement reduces noise from tire/pavement interaction compared to traditional pavements. Noise reduction usually comes from the type of surface texture used on the pavements” (WSDOT, 2005)
What is Noise?
“In the simplest terms, noise is any unwanted sound. The definition of unwanted sound is subjective, varying from person to person: one person’s music is another person’s noise. Different noises produce different reactions depending both on their intensity (how loud they are) and on their frequency distribution (also described as pitch, varying from low to high). Human hearing tends to be more sensitive to higher pitches of sound, like emergency sirens or tire squeal, and less sensitive to lower pitches, like the base notes on the stereo. At the same intensity of sound, a higher pitch can sound louder or more annoying than a lower pitch.” (WSDOT, 2005)
Effects of Noise
“Environmental noise at high intensities directly affects human health by causing hearing loss. Prolonged exposure to very high levels of environmental noise can cause hearing loss. The EPA has established a protective level of 70 dBA Leq (24), below which hearing is conserved for exposure over a 40-year period (U.S. EPA, 1974). Although scientific evidence is not currently conclusive, noise is suspected of causing or aggravating other diseases. Environmental noise indirectly affects human welfare by interfering with sleep, thought, and conversation. The FHWA noise abatement criteria are based on speech interference, which is a well-documented impact that is relatively reproducible in human response studies.
The use of quiet paving surfaces, assuming that the reductions are audible and lasting, allows residences and other sensitive listeners to experience a quieter outdoor environment even in those places where it would be infeasible to place a noise wall or berm. Examples may include homes located on hillside overlooking the highway or near wetlands or lakes that preclude construction. The use of quieter paving surfaces may also allow for reduction in proposed noise barrier heights (which can be imposing at 20 – 30 feet in height) and reduced noise barrier costs due to decreased square footage and smaller foundation requirements.” (WSDOT, 2004)
Measurements of Pavement Noise
Information contained in this section is from WSDOT, 2005 on Quieter Pavements
A logarithmic scale (for noise, this is referred to as the A-scale) is used to represent sound levels and is measured in decibels (dB). The curve that describes the A-scale roughly corresponds to the response of the human ear to sound. Studies have shown that when people make judgments about how noisy a source is that their judgments correspond quite well to the A-scale sound levels. The decibel scale ranges from 0 dBA, the threshold of human hearing, to 140 dBA where serious hearing damage can occur. The average human ear can only differentiate between two sound levels that are at least three dBA different in loudness. Table 1 represents this scale and some of the levels associated with various daily activities.
Table 1. Noise Levels Associated with Common Activities
|Activity||Noise Level (dBA)|
|Threshold of pain||140|
|Jet flyover at 1000 feet||110|
|Gas Lawnmover at three feet||100|
|Diesel truck at 50 feet||90|
|Motocycle passing at 50 feet||85|
|Blender at three feet||85|
|Car traveling 60 mph passing at 50 feet||80|
|Heavy traffic at 300 feet||60|
|Quiet living room||40|
- Traffic noise typically ranges between 55 and 80 decibels along a highway right of way line.
Because of the logarithmic decibel scale, a doubling of the noise sources only increases noise levels by three dBA. Figure 1 illustrates the effects of adding two noise sources. If the noise level from one source of sound (a blender) measured at 3 feet from the blender is 85 dBA, then the noise level from two blenders would be 88 dBA, and the noise level from three blenders would increase to 89.8 dBA.
For a single noise source, such as a blender, the noise is reduced by 6 dBA when the distance away from the source is doubled and is 9.5 dBA at three times the distance. Thus, if you have a blender that has a sound level of 85 dBA at 3 feet, when you move 6 feet away from the blender, the noise level would be 79 dBA, and if you move three times the distance (9 feet) away from the blender, the noise level would be 75.5 dBA. This is illustrated in Figure 2.
Roadway noise, however, acts in a different manner. As a vehicle passes by a point, the noise is reaching the point from all along the roadway or from each point where the vehicle was. As the distance from the noise source increases, the noise level decreases at a lower rate than from a single point noise source. For paved surfaces, the doubling of the distance would result in a 3-dBA reduction in the noise level. Thus, if a point 16 feet from the center of the noise source (the center of the lane) of the roadway has a noise level of 85 dBA, then a point 32 feet from the edge of the roadway would have a noise level of 82 dBA. This is illustrated in Figure 3.
The amount of traffic noise depends on traffic volume, speed, and the type of vehicle. Generally, an increase in volume, speed, or vehicle size increases traffic noise levels. Vehicle noise is a combination of sounds from the engine, exhaust, and tires. Other conditions affecting traffic noise include defective mufflers, steep grades, terrain, vegetation, distance from the roadway, and shielding by barriers and buildings.
Field Measurement of Road Noise
Three methods commonly used for measuring pavement noise levels in the field are:
Statistical Pass-by Procedure — The statistical pass-by method consists of placing microphones at a defined height and distance from the vehicle path at the side of the roadway.
Single Vehicle Pass-by Method — With the single vehicle pass-by method, noise from cars and light trucks is typically measured at a specially designed test site. The vehicle approaches the site at a precise speed and gear. A sound level meter is set at a specified distance from the center of the travel path and captures the sound level of the vehicle as it passes.
Near-field Techniques — Near-field techniques, such as the close proximity method (CPX), measure sound pressure using microphones mounted on the vehicle near the vehicle tire.
OBSI stands for On-Board Sound Intensity, a method to measure tire/pavement noise at the source. The method was developed at General Motors, but the California Department of Transportation (Caltrans) funded the research to convert it into a method applicable in pavement engineering. Most of the adjustments to the original test method have resulted from the work of Dr. Paul Donavan. In 2005 Caltrans established a Quiet Pavement Research Program, and the Partnered Pavement Research Center became capable of testing OBSI.
Where does Highway Noise Come From?
Highway traffic noise is generated from three main sources:
- The contact-point between the tire and the road (tire/pavement noise).
- The vehicle engine.
- The exhaust system.
The tire/pavement noise accounts for 75 to 90 percent of the overall noise energy (Caltrans, 2003) when driving over 50 miles per hour. The frequency and intensity of tire/road noise depends on a variety of factors:
- Roadway roughness
- Tire tread configuration
- Studded tires
- Roadway surface openings (voids)
- Joints in the PCC pavements
- Speed of traveling vehicles
- Size of tires (amount of rubber on the road)
According to Brennan et al., cars are quieter than medium trucks and multi-axle trucks, mainly due to fewer tires. There is about a 5.6 dBA increase from cars to dual-axle vehicles and another 5.6 dBA increase to multi-axle vehicles. This is supported by Kandahl (2003), where he notes that trucks are a louder source of noise, but since the traffic is primarily comprised of cars, this noise can be more disruptive because of the constant whine.
What Types of Quieter pavements Are In Use Today?
“The majority of quieter pavement designs use a “negative texture,” and the most common of these is the open graded friction courses (OGFC). OGFC use small holes, or air voids, in the pavement to provide a sound absorbing negative texture. OGFC can be made with conventional liquid asphalts or with polymer-modified asphalts, including rubberized asphalts. Rubberized OGFC use finely ground rubber from used tires to modify the asphalt binder in the pavement mixture.
These OGFC varieties differ from traditional dense-grade HMA by having much higher air voids. Typical dense-grade HMA has air voids that begin at 8 percent and decrease over the life of the pavement to approximately four percent. OGFC start with air voids from 10 to 22 percent and see little decrease over the life of the pavement. Most modern OGFC have air voids in from 15 to 22 percent.” (WSDOT, 2005)
- Quieter Pavements: Options & Challenges for Washington State. Washington State.↵
- Sound Engineering: Innovation in Pavements. California Transportation Journal, Jan- Mar 2003, pp. 34-37.http://www.dot.ca.gov/dist07/aboutdist7/pubs/journals/jan_mar_2003/janmar03.pdf (accessed August 25, 2004).*Quieter Pavements: Options and Challenges for Washington State, May 2005.↵
- How Asphalt Pavement Mitigate Tire-Pavement Noise. Better Roads, v. 73, no. 11, 2003, pp. s16-s22.↵