What is Tire-Pavement Noise?
Definition
Tire-pavement noise is the sound that a rolling tire makes where it meets the pavement surface. It is one of three sources of vehicle noise. The other two are air moving over and around the vehicle, and the engine, exhaust and drivetrain. On a road, a large part of the vehicle noise comes from the tire-pavement interaction, especially above 45 mph (about 72 km/h).
How the noise forms
The impact mechanism is dominant for the noise that travels away from the vehicle. Bumps in the road surface or in the tire tread make the tire vibrate, and the tire radiates sound. Texture with wavelengths of about 10 to 50 mm is mostly responsible.
The aerodynamic mechanisms add to this. As the tire rolls, it traps air in voids between the tread and the pavement and ejects it quickly. The voids can also resonate.
A perfectly flat road is not a quiet road, and it would also have low friction.
What changes the noise
Texture is the largest contributor. Porosity and stiffness also matter. A porous pavement absorbs sound and gives the trapped air a place to go. An open-graded friction course (OGFC) is a porous surface layer. When new, it can reduce sound by about 3 dB(A) compared with a dense-graded mix. Clogging and raveling reduce this benefit over time.
How it is measured
- CPX (close-proximity method, ISO 11819-2): microphones in an insulated enclosure on a trailer, next to the tire. It applies to free-flowing traffic at constant speeds of 40 km/h and upwards.
- OBSI (on-board sound intensity): microphones at the leading and trailing edges of the contact patch, usually tested at 60 mph.
- SPB (statistical pass-by, ISO 11819-1): microphones at the roadside. It records engine and exhaust noise as well.
Runways
The sources used for this page describe roads. They give no noise values for runways. CS ADR-DSN.B.090 (c) recommends an average surface texture depth of at least 1.0 mm for a new runway surface. The same paragraph sets requirements for irregularities, friction and grooves. It gives no noise value.
Frequently Asked Questions
- What causes tire-pavement noise?
- Two groups of mechanisms cause it. In the impact mechanism, bumps in the road surface or the tire tread make the tire vibrate, and the tire radiates sound. In the aerodynamic mechanisms, air that is trapped between the tread and the pavement is ejected quickly, and cavities can resonate. Pavement texture is the largest single contributor.
- How is tire-pavement noise measured?
- Three methods are common. The close-proximity (CPX) method and the on-board sound intensity (OBSI) method put microphones next to the tire. The statistical pass-by (SPB) method puts microphones at the roadside. CPX and OBSI measure only the tire-pavement noise. SPB also records engine and exhaust noise.
- Does a quiet pavement stay quiet?
- Not always. A new open-graded friction course can reduce sound by about 3 dB(A) compared with a dense-graded mix. Clogging and raveling reduce this benefit, and a US state-of-practice article reports that it may last only 5 to 7 years. An open-graded surface can later become louder than a dense-graded one.
References
- fhwa-microphones
- Pavements - Microphones (MP) FHWA
- fhwa-tops-ogfc
- Open-Graded Friction Course How-To Document (November 2022) FHWA
- rasmussen-physics-today-2009
- What causes road noise? (Physics Today, December 2009, pp. 66-67) R. O. Rasmussen and P. R. Donavan, American Institute of Physics
- afnor-iso-11819-2
- ISO 11819-2:2017, Acoustics - Measurement of the influence of road surfaces on traffic noise - Part 2: The close-proximity method ISO, catalogue entry on the AFNOR store
- easa-ear-aerodromes
- Easy Access Rules for Aerodromes (Regulation (EU) No 139/2014), including CS-ADR-DSN EASA
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