Internoise04, 22-25 Aug 2004, Prag

Contributions to Session NS4-Quiet Traffic, Chair: Heinrich B. Weyer

Author(s)

Title of presentation

Heinzelmann

Quiet Traffic – Goals and Focus of Research in Germany

Michel et al.

Localisation of moving sound sources with phased microphone arrays

Griefahn

Research Network 'Quiet Traffic' – Research on the Effects of Noise

Glaeser

Research Association "Quiet Road traffic"

Hecht

Reduction of Vehicle Noise - Needs and Possibilities in a Situation of Speed- and Density Increase

Saueressig

Investigating aircraft noise reduction measures – steps towards The Quiet Aircraft

Noise generated by traffic has become a serious problem in today`s society. About 80 million EU citizens are exposed to unacceptably high levels of noise. The economic costs to society are estimated to more than 12 billion €. In Germany, 2/3 of the population complain about road noise, 1/3 about air traffic noise and ¼ about railway noise.

By the expected traffic growth in the next years, noise may become a bottleneck for mobility and economic development in Europe as a whole and especially in Germany. In addition the effects of noise can limit the quality of life, cause stress, reduce human productivity and may even lead to serious health problems.

Less noise in spite of more traffic is a matter of priority for a policy taking into account sustainability, efficiency and competitiveness. Within the framework of the research programme “Mobility and Traffic” the German Federal Ministry for Education and Research supports noise reduction in road, railway and air traffic focussed on noise abatement at the source.

Coordinated and interdisciplinary efforts promise to be the most efficient and goal-oriented approach. In the German research network “Quiet Traffic”, established in 1999, so far 70 partners have joined from academia, industry, operators and agencies. The aims are to develop noise reduction methods, quiet traffic routes and operational procedures; to recommend rules and standards; and to improve traffic management and control.

The Paper will give an overview about strategies, goals and focus of current research efforts on noise reduction in Germany.

The phased microphone array is becoming a standard method for the investigation of the sound emission of railways, aircraft, and road vehicles. It is the only method that allows an identification of the noise sources when the vehicle is in motion. Wheel-rail-noise and aerodynamic noise of railways, airframe noise and installed engine noise of aircraft, tyre-road noise of automobiles are typical examples. The method has improved in the past years with the appearance of data acquisition systems capable of sampling a large number of signals and the use of relatively cheap Electret microphones. In addition, the data reduction computing times have decreased substantially with modern fast personal computers.

The requirements for source localisation on aircraft are especially high. The large flyover altitudes require large array dimensions and large number of microphones. The system that has been developed by DLR for this application will be presented. A number of up to 496 microphones can be used. It will be demonstrated that nested arrays are essential for a good signal-to-noise ratio and a quantitative analysis. The spatial resolution and the requirements for the data acquisition are derived. The limits and possibilities for obtaining quantitative results are also demonstrated. Various examples for the distribution of noise sources on aircraft, high-speed trains, and motor vehicles will be shown and discussed.

The research network 'Quiet Traffic' aims at the reduction of noise though traffic density increases dramatically within the forthcoming years. As noise effects depend on many acoustic and non-acoustic factors, the quantification of the significance of levels, frequency spectra, type of noise, noise sensitivity during day and night is an essential basis for directed developments and establishments of technical and operational abatement measures. The section 'Noise Effects' is focussed on the following areas where first results will be presented:

Frequency spectra. Road noise, presented with various traffic densities reduced performance above equivalent noise levels of 60 dB(A) where the damping of lower frequencies caused a trend towards lower annoyance in children. 

Diurnally varying noise effects. The temporal variance of sensitivity which might lead to suitable itineraries for air and rail traffic is studied in the field and – concerning sleep – in the laboratory.

Effect-equivalent assessment of different noises. Due to social surveys road noise annoys more than rail noise, where the differences increase with noise levels. As all partners apply road and rail noise this relation is studied for communication, cognitive performance, and sleep. Very first results on noise-induced sleep disturbances do not confirm the rail bonus.

Effect-equivalent assessment of simultanously occurring noises. Though many residents are usually exposed to more than one traffic noise, assessments concern only one source. As the equivalent noise level cannot predict the overall effect, a multicenter study focusses on the development of a model for the assessment of simultaneously occurring road and rail noises.

Dr.-Ing. Peter Reichelt, President's representative and head of the Road Engineering Department at the Federal Highway Research Institute

The aim of the research association designated Quiet Road Traffic was to reduce tyre/carriageway noise levels by 3 dB(A).
This research program was intended to develop and test wide-ranging measures proving to be of tangible benefit for the public in the foreseeable future.
In this process, it was necessary to consider that road surfaces last approximately 15 – 20 years, vehicles 8 - 12 years and tyres 50,000 – 80,000 km.

As part of the Quiet Road Traffic project, we were also able to optimize tyres in terms of noise reduction, taking into account all types of road surfaces commonly found in Germany.
Depending on the road surface involved, a noise reduction of 1-2 dB(A) is achievable.

On the vehicle itself, we were able to optimize the wheel housing's noise level. The automobile manufacturer VW developed a housing fit for serial production, having established a noise reduction potential of –0.5 dB(A) for it.

In their totality, the results indicate a noise reduction potential of about 3 dB(A) provided by the synergy between all partners.

Public transport must be attractive and cost efficient. Also the environmental requirements must be fulfilled.
Attractiveness is increased with frequent services and high speeds. Cost efficiency also is increased with speed increase: employees are paid on at time basis and passengers pay distance oriented. At a given operation frequency driving faster also reduces the number of trains needed and therefore the needed capital costs are reduced.
This all is positive in an economical sense, but most noise sources are emitting more noise with higher speeds.
Regarding the maximum noise levels high-speed vehicles need higher installed power. More power also needs more space in the vehicles. Noise reduction of the power system is not only important because of the higher power-rates but also because of the limited space available.
Rolling noise is speed dependent according to the 30 log v – law.

Squeal of disk brakes is not only bothering travellers standing at platforms but also residents nearby stations.
Additionally to this topics already finished or at least at work further questions are being prepared as noise dependent track prices and special curve noise issues.