Road vehicle and tyre noise

Noise homepage

Road vehicle noise

Road traffic noise is the major source of environmental noise exposure. Despite European vehicle noise standards being introduced in the early 1970s, road noise levels have not decreased. Technological progress has been largely cancelled out by increases in traffic and a trend towards heavier and more powerful vehicles and wider tyres.

Watch videos about how tyres are tested and the range of noise emissions from different types of tyre.

By combining different measures including low noise road surfaces; stricter noise standards for vehicles and tyres, and reducing traffic speed, a general reduction of road traffic noise of 10dB(A) could be possible within 10-15 years. This would be equivalent to reducing noise to one tenth of current levels [1].

Road noise arises from three sources on vehicles:

• Propulsion noise (engine, powertrain, exhaust and intake systems)
• Tyre/road contact noise
• Aerodynamic noise

The engine noise is the dominant source at lower speeds (under 30km/h for passenger cars / under 50km/h for lorries), tyre noise dominates above that, and aerodynamic noise becomes louder as a function of the vehicle speed. [2]

Vehicle noise standards are laid down in Directive 70/157/EEC and subsequent amendments [3], which regulates the technical approval of new vehicles and currently sets noise emission limits of 74dB(A) for passenger cars and 80dB(A) for trucks. The standards for trucks have been somewhat more effective than for cars. The noise limits include all sources of noise from the vehicle.

In practice, the EU directive follows Regulation N°51 of the United Nations Economic Commission for Europe (UN-ECE) which harmonises rules for road vehicle sound emissions. Regulation 51 is defined at international level by the UN-ECE World Forum for Harmonisation of Vehicle Regulations. While type-approval noise limits have been gradually tightened over the years (by a reduction of more than 10dB(A) for certain vehicles), no improvement has been made regarding overall exposure to noise generated by road vehicles, due largely to a significant increase in road traffic and a trend towards larger, heavier and more powerful vehicles. In fact, the introduction and regular tightening of these limits allowed for a harmonisation of the road vehicle fleet regarding noise emission characteristics, but did not prove to be a strong technical drive towards quieter vehicles, particularly in the case of delivery vans and trucks. [4]

The test cycle for vehicle certification on noise levels does not accurately reflect real world driving conditions. The current test cycle does not include provision for evaluating noise performance in typical urban stop-start traffic situations at lower speeds, where engine noise is the dominant source. Another major failing is that the test parameters are set in such a way that vehicles can be designed to pass the test but are considerably louder when driven on the road. This urgently needs to change to prevent this kind of cheating, known as “cycle beating”, which is allowing dangerously loud vehicles on to our roads.

The development of a new real-world test cycle is having the effect of delaying the possibility of introducing tighter limits for road vehicle noise emissions. There is a general consensus in the UN-ECE Working Party on Noise that equivalent values must be identified between the new and old test procedures, before tightening the limits can be discussed. A two year data collection period has just begun. The European Commission will collect the results. After two years at the latest (in theory, it could also be earlier), equivalent values for the new test will be identified.

Tyre noise

Tyre rolling noise emissions have increased over time, which is predominantly due to increased use of wider tyres. As the tyre/road contact begins to dominate the noise emission above 30km/h for passenger cars and above 50km/h for lorries, it was deemed necessary to regulate tyre/road noise separately as well as its role in overall vehicle noise [2]. Therefore Directive 2001/43/EC complements the vehicle noise standards by setting a test procedure and noise limit values for tyre rolling noise.

Hear the difference!

Typical car tyre: -2db(A)
Quiet car tyre: -7db(A)

Typical truck tyre: +1db(A)
Quiet truck tyre: -3db(A)

The directive states that the limit values should be reviewed and revised 36 months after 2001/43 enters into force [5]. This deadline passed in summer 2004. A report making recommendations for the revision of the limit values and other aspects of the directive was presented to the European Commission in 2006 [6]. The feasibility study outlines a proposal for two phases of stricter limit values for 2008 and 2012, for tyres for passenger cars and trucks. The study recommends limit values which are equivalent to effective noise reductions of (taking into account different tyre classes and dimensions):

• Passenger car tyres: 2.5-5.5dB(A)
• Commercial vehicle tyres: 5.5-6.5dB(A)

The report also demonstrates that;

• Quieter tyres do not compromise safety (wet grip, aquaplaning) or fuel economy (rolling resistance).
• The proposed limit values for tyres for cars and trucks would lead to an estimated overall noise reduction of up to 3dB(A), which is equivalent to cutting the current noise level by half, or halving the number of vehicles on the roads.
• Enforcing these standards will not incur huge costs. The technologies and products have already been developed, and the industry is prepared.
• Conservative scenarios estimate the societal benefit of quieter car tyres to be worth at least €48billion, and up to €123billion, across the EU over the period 2010-2022. Even the most cautious calculations point to benefits outweighing costs by 24:1. These figures do not even include the savings for health services, or attribute a value to annoyance or stress.
• Benefits will be further magnified when quieter tyres are used on silent road surfaces.

Despite these convincing arguments, a proposal is not yet forthcoming.

The current limit values for tyre rolling noise have had minimal impact on noise levels. 96% of commercially available tyres on today’s market meet the limit values [6]. 

The graph illustrates that approximately half of the sample are over 3dB(A) quieter than the current limits, meaning that they produce less than half the noise currently permitted. This shows that the standards are lagging behind technologies that are already available and that the current limits are not serving their intended purpose. Tyre producers currently have no incentive to produce quieter tyres. Some tyres are as much as 8dB(A) below the limit, but as there is no noise labeling and hardly any noise information available to consumers, low noise is not exploited as a marketable attribute.

There are two principal reasons why stricter tyre rolling noise limits are urgently needed:

• Tyre rolling noise is generally the dominant source of noise from road vehicles at medium and high speeds.
• As the lifespan of tyres is shorter than that for vehicles, addressing tyre noise standards will be one of the fastest ways to achieve road noise reductions.

The way forward should be first to achieve effective standards based on the current status of technological development. The proposed indicative limit values for 2008 are already achieved by the majority of tyres currently on the market. 76% of the passenger car tyres on the market in 2004 would already meet the 2008 standards. In fact, 35% already meet the proposed 2012 standards [6]. This demonstrates that the Commission should be even more ambitious in their proposal because low-noise models have already gained type approval according to road safety requirements, sales of these models proves that they are commercially viable.

Future standards should serve as an incentive for innovation and encourage technological development. The best technology currently available (which also fulfills safety and other product approval requirements) is 8dB(A) below the current limit values [7]. Innovations like this should set the pace for the market. Outlining future phases of tightening in advance also provides certainty for the industry and consumers.

The report to the Commission also recommends inclusion of labeling of tyres, in the form of noise levels stamped on the sidewall, or a “low noise” label for the quietest models. At present, even if consumers request advice or information on noise levels of tyre models, sales staff are not given this information by the manufacturers. Consumer awareness of noise emissions from tyres can easily be increased by product labeling and a framework for incentives that Member States can grant to quieter tyres. Such action would clarify the range of consumer choice, similar schemes have been seen to be successful for noise ratings of electrical goods.

Links

Road traffic noise (responsibility of EC Directorate-General Enterprise):

• Motor Vehicles - 70/157/EEC
• Motor Cycles - 97/24/EC
• Tyres for motor vehicles and their trailers and their fitting - 2001/43/EC

European Commission funded projects:

• RATIN (tyres)
• FEHRL report on tyre/road noise (2006): Report and Annexes
• Q-CITY (urban transport noise)
• SILENCE (urban transport noise)

References

[1] Amundesen, A. and Klaeboe, R. (2005): A Nordic perspective on noise reduction at the source, Report 806/2005, Institute of Transport Economics (TOI, Oslo).
[2] Sandberg, U., Ejsmont, J. A. (2002) Tyre/Road Noise Reference Book (www.informex.info )
[3] Directive 70/157/EEC and subsequent amendments
[4] UN-ECE WP29: World Forum for Harmonisation of Vehicle Regulations (WP29) How it works, How to join it, Published by United Nations, New York and Geneva, 2002.
[5] Article 3.2, Directive 2001/43/EC of the European Parliament and of the Council of 27 June 2001 amending Council Directive 92/23/EEC relating to tyres for motor vehicles and their trailers and to their fitting, OJ L 211 , 04.08.2001 P. 0025 – 0046.
[6] FEHRL (2006): Study SI2.408210 Tyre/Road Noise Report and Annexes
[7] IPG noise site