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Road vehicle and tyre noise
Noise
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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 [3] 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] [4].
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] [5]
Vehicle noise standards are laid down in Directive 70/157/EEC and
subsequent amendments [3] [6], 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] [7]
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] [8].
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!
[9] Typical car tyre:
-2db(A)
[10] Quiet car tyre:
-7db(A)
[11] Typical truck tyre:
+1db(A)
[12] 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] [13].
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] [14].
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] [15].
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] [16]. 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] [17].
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 [18]
- Motor Cycles - 97/24/EC [19]
- Tyres for motor vehicles and their trailers and their
fitting -
2001/43/EC [20]
European Commission
funded projects:
- RATIN [21]
(tyres)
- FEHRL report on tyre/road noise (2006): Report [22]
and Annexes [23]
- Q-CITY [24]
(urban transport noise)
- SILENCE [25]
(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 [26] )
[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 [27]
and Annexes [28]
[7] IPG
noise site
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