How loud can cars actually be?

Due to current initiative by the European Commission to update noise legislation, the aspect of noise control is receiving greater attention. Noise has many manifestations. The World Health Organization (WHO), which has been investigating the effects of latent noise pollution on one's health for many years, offers recommendations on noise control. The EU addresses this type of noise exposure via the noise-mapping regulation, and obliges the Member States to regularly assess the noise situation in larger cities as well as along major transport routes, and to draw up noise action plans based on these assessments.

In the perception among the population, however, this type of environmental pollution plays only a subordinate role compared to other environmental issues. At the moment, the public does put a stronger focus on noise pollution resulting from specific events, such as motorcycle noise and noise due to the inappropriate driving style of so-called "poser cars," which above all involves manipulated exhaust systems.

In the emerging debate about updating noise legislation, both aspects – noise pollution and noise nuisance – must be addressed. Current noise legislation already reflects both aspects. For one, vehicles submitted for type approval are measured in a manner that determines the noise level representative of the use of the vehicle under urban operating conditions. The defined noise limits are representative of 90% of all driving conditions in urban traffic. Likewise, passenger cars are subject to expansive requirements within a broad range of operating conditions to exclude unreasonable noise emissions.

There is a specific level of noise emitted by vehicles that can never be completely suppressed. Also, for safety reasons a "zero emission" of noise is not desirable. This dichotomy is taken into account in noise legislation. Such legislation not only provides for maximum levels in regard to environmental protection but, in the EU as of 7/2021, also prescribes a minimum noise level for the first registration of fully electric vehicles to ensure that the vehicles are sufficiently perceptible in traffic. Therefore, it must be kept in mind when updating the noise legislation that if the maximum levels are reduced further, more and more products will fall below the minimum-noise requirements and will then have to be equipped with supplementary sound generators.

The main source of noise in modern vehicles is the sound of the tire on the road. The road surface plays a prominent role in this. The material type and surface finish of a road significantly influence the noise of a moving vehicle. A low rolling noise can only be achieved if, in addition to the latest tire technologies, all available technologies for noise reduction are used on the road surface. In both cases – road surface and tires – different and sometimes opposing aspects have to be considered.

The primary task of the tire is to move the vehicle safely on the road: Braking distance, curve stability, and both dry and wet grip are just a few criteria that every experienced driver is familiar with. In addition, a long service life and low rolling resistance to reduce fuel consumption are also important customer requirements. All studies show that the isolated optimization of individual criteria is not possible with tires. Further progress towards quieter tires will inevitably come at the expense of other parameters, such as driving safety and environmental friendliness. Any further tightening of noise regulations will have far-reaching consequences and endanger the attainment of the CO₂ targets and, in turn, the fulfillment of the EU's Green Deal.

When it comes to road construction, the recent years have seen the development of some new, interesting technologies for "low-noise" road surfaces. These road surfaces are mainly suitable for urban areas, where they are particularly quiet but also both anti-skid and durable.  

Sounds are caused by the physical oscillation of air molecules and are therefore local: The spread of sound is spatially limited. This offers further possibilities for influencing noise abatement by minimizing the spread of noise.

In the field of building technology, approaches include noise-absorbing facades as well as excellent window technologies and ventilation concepts that have accompanied the revision of the Energy Saving Ordinance (EnEV). Both technologies can help to significantly improve noise protection along busy roads. This means that directly applicable synergy effects from other areas already exist. If we are planning for a future with "green and smart cities," aspects like these must also be included when forecasting noise reduction needs.

Automotive manufacturers and their suppliers are aware of their responsibility for a future-oriented society and the corresponding challenges posed. For the potential for quieter vehicles to both be evident in daily traffic and to reach the affected population in a tangible and measurable way necessitates support from other areas of society – including, above all, politics. In concrete terms, this means:

• Systematic use of low-noise road surfaces, especially in "noise hotspots."
• Greater consideration of noise-reduction potentials in traffic-flow planning. 
• Use of new technologies to reduce the spread of noise in urban environments. 
• Consistent prosecution of illegal manipulations and reckless driving behavior.