When the intensity of noise and duration of the exposition to noise increase, the effects on human beings increase as well. Residents will be more annoyed, the closer they live to a railway line or a motorway. And also: the passage of a single train per hour will be less annoying than a train every five minutes. These conclusions are usually presented as so-called dose-response relationships. Such relations were derived from field studies in the nineteen seventies. Usually they relate self-reported annoyance (assessed on the basis of score in a questionnaire) to long term average noise level.
In the early eighties it was found, in several of these field studies, that at equal long term average exposure, railway noise caused fewer people being annoyed than road traffic noise. This result was the basis for a differentiation in legal noise limits between road and rail traffic; the difference usually amounts to 5 dB. Some 6 member states introduced this differentiation, either in limits or in the prediction method. In Germany, the limits are identical for road and rail noise, but the prediction method introduces the 5 dB correction factor. This correction factor has been given the name “railway bonus”, a somewhat unlucky choice, since many people think that this correction factor is merely reflecting the environmental benefit of rail transport relative to road transport. As the above introduction illustrates, there are other, more fundamental reasons for this factor.
Over time, the justification of the noise annoyance correction factor was frequently questioned. Certainly at times, when the public discussion on railway noise increased, for example when high speed lines were planned, or currently in situations with rapid growth of freight transport. UIC has commissioned a study from DHV in The Netherlands, reviewing the available references on this topic, both recent and historical. The study concludes, on the basis of numerous international references, that most field studies confirm that the correction factor is still justified, even when traffic circumstances have changed. This applies to the classical relations, where long term average noise levels are currently expressed as Lden (day-evening-night level, with penalties for evening and night included), and “annoyance” is the self reported result of a score list, currently standardized by the ICBEN . Moreover, these two parameters invariably show rather good correlation.
Poor correlation is found, when other parameters are chosen. For example, there is a tendency to apply maximum noise levels instead of energy equivalent levels as the dose parameter. Particularly for night time noise, a wide range of parameters can be found, registering e.g. sleep disturbances. When comparing sleep near a railway line to sleep near a road, the window setting often disturbs the picture: most people near a busy road sleep with windows closed.
More study is needed to find ways to company the regular dose parameters such as Lden to the other, more incidental parameters. For the time being, there are no fundamental indications that the railway noise annoyance correction factor should be omitted.
The Silence project focused on the development of noise reduction solutions for rail and road, more particularly for urban situations, applying a global approach, with work packages dealing with noise sources to be evaluated, and work packages on global modelling, noise annoyance and noise mapping.
The general approach of the project was to identify and establish a ranking of the main noise sources, and to develop solutions of reduction for them. In a second step, the impact of these solutions on the total noise level could be evaluated using a global model. For this objective, the VAMPPASS tool, created during the project, delivered usual information like sound pressure level, spectrum and signature, but also sound samples of the pass-by, necessary for annoyance tests.
Prototypes of silent trains and silent tracks have been tested with the tool and some promising solutions have been found and presented all along the day, like actions on the diesel powerpack (encapsulation…), modification of the cooling system, use of wheel dampers for the train, and track dampers for the track. These solutions have been tested by retrofitting existing trains, but some of these solutions could be more efficient being planned since the creation phase of new vehicles.
As examples, the following noise reduction can be expected on the total noise level:
5 dB(A) by reducing the rolling noise with wheel and rail dampers,
8 dB(A) for a DMU at 80 kph, combining the different solutions tested.
The case of depots has also been studied.
Access to SILENCE website.
Curve squeal is an intense tonal noise that may occur on curves or on switches. The high noise level causes annoyance for people living in the vicinity of a squealing railway track as well as for passengers waiting in stations with curves. The character of the noise is very intense with high frequencies (up to 10,000 Hz) and high amplitudes that can be up to 100 dB(A) in 10 m distance.
To answer to this problem, the UIC Combating Curve Squeal project was designed to find measures against the annoying high-pitched noise created during pass-bys of trains in certain curves. A first phase, completed in 2003, was aimed at analyzing existing knowledge and developing models while the second phase, described in the report below, intended to increase confidence in selected mitigation measures.
A selection of friction modifiers and water were tested on two different rigs and under field conditions in Switzerland, France and the UK.
In conclusion, no optimal solutions could be found that would work under all circumstances. For each curve the trade-off between performance, dosage and costs must therefore be evaluated separately.
Appendices are available here
Status and options for the reduction of noise emission from the existing European rail freight wagon fleet, 2004
This report investigates the status and options for retrofitting of the existing European rail freight fleet based on a study commissioned by the European Commission and jointly funded together with the railways (UIC and CER), the wagon owners (UIP and UIRR) and the manufacturers (UNIFE). AEA Technology has been commissioned as consultant including the specific task of performing an independent third party assessment of the existing activities and results of the rail sector in the field of noise.
The STAIRRS proposal was submitted in response to the EU´s 5th Framework Programme "Sustainable Mobility and Intermodality: Competitive and Sustainable Growth", where the need was identified for a study to assess the relative effectiveness, benefits and costs of a number of railway noise mitigation options applied to vehicles or track.
The outcome of the project was to provide a cost benefit software tool to assess various noise mitigation strategies, to provide measurement methodologies to enable characterization of railway vehicles and railway track separately and to develop a consensus between legislators, railway operators, railway infrastructure managers and the railway supply industry on the means of balancing the environmental needs of the Community with the noise mitigation options available and the costs of their implementation.
To read more about the background of the project please visit: STAIRRS website.
The conclusions of the project was as following:
- The most efficient noise mitigation step to take is to ensure that freight trains have smooth wheels. By itself however it does not achieve sufficient noise reduction to achieve targets being placed on the railways and must be supplemented by further measures taken on wheels and tracks.
- A combination of smooth wheels, rail absorbers and optimised wheels is more effective than the use of noise barriers, even when 4 m high, at a lower cost.
A series of workshops were held within the project with the following conclusions:
- Pressure from the implementation of noise creation legislation for railways is essential step for reducing noise levels. It was recognized, however, that some change to the EU funding policies would be needed so that where it was shown to be cost effective, financial support should be given to noise mitigation at source instead of it being used to construct of line side noise barriers.
- Application of operational constraints, even locally, in order to reduce noise is not consistent with the commercial requirements of railway operation particularly whilst attempting to fulfill the objective of transferring traffic from road to rail and needing to maintain competitive with respect to road transport.
This report sets out current knowledge of the phenomenon of railway noise and the potential of technical measures to mitigate it. The report also contains proposals for future achievable and affordable noise creation limits which are based on this knowledge.
The conclusions of the report is as following:
- The developing EU policy framework for environmental noise will require noise creation limits for rail vehicles. It is essential that the limit values adopted are technically feasible and affordable.
- Measuring noise created by moving trains is problematic; empirical observations (for the same type of train at the same time) often show considerable variability. Any discussion about noise creation values must acknowledge this variability.
- Several countries have introduced noise creation limits. They have limited effect in the absence of a Europe-wide initiative.
- There is considerable empirical knowledge of the noise performance of existing trains; the results of collaborative railway research endeavour over many years have identified a number of technical measures shich will reduce noise creation.
- Application of these measures to existing vehicles is much more expensive than incorporation in new designs.
- The paper proposes limit values for noise creation by conventional vehicles, by high speed trains and by stationary trains. These are technically feasible and will be affordable when incorporated in the specification of new designs.
- The paper also proposes limit values for noise creation by freight vehicles, which are retrofitted. Although technically feasible retrofitting with the existing technology is not cost neutral to date. To find financing solutions is an essential prerequisite if an early reduction in the noise created by the existing freight vehicles is to be achieved.
This report describes the noise research carried out by ERRI and a number of European railways until 1998. It evaluates the options available to aim for a target of a 20 dB(A) noise reduction for freight vehicles compared with current levels in 1998. The paper concentrates on work that has, in the main, been funded by the UIC but also identifies certain national initiatives.
The summary indicates that a great deal of work has been carried out and a high level of knowledge has been accumulated to find effective solutions to reduce railway noise in its creation and reception.
There are still areas of research where work can be identified to further reduce railway noise but these need to be prioritized to meet strategic aims. However it is evident that social and legislative pressures will continue to determine that railways will need to concentrate further efforts on noise reduction techniques.