Noise reduction in rail networks

Source of the noise and vibration

Technology for a Quieter America ¹ explains how noise is created by a coupling between a moving structure and air. They theorize that although noise is generated by turbulence in high-speed flows, more noise comes from the mechanical motion created by forces acting on structures. This can cause exceptionally complex noise, such as those from a panel on a machine.

According to Technology for a Quieter America, ¹ a study sponsored by the United States Environmental Protection Agency (EPA) compares the noise from rail transportation with that from other transportation modes. The study concludes that rail noise affects more than 4 million people in the United States, urban mass transit system affects 2 million, and noise from railroad operations and yards affects another 2 million. Even greater numbers of people are affected by train horns at railway crossings—estimated at 6 million by the Federal Railroad Administration (FRA). Therefore, Technology for a Quieter America ¹ concludes that nearly 10 million people are affected by noise from rail transportation in the United States at present.

As fundamental rail technology involves steel wheels rolling on steel rails, Technology for a Quieter America ¹ surmises the noise from wheels and rails and categorizes them into three major types:

Another source of squeal noise is the braking system, which causes a metal shoe to clamp on to a running wheel when braking, with the friction between the two creating vibrations that allows both the brake shoe and the wheel to resonate at their natural frequencies.

The rail system has many other sources of noise and vibration. According to Technology for a Quieter America, ¹ this may be caused by mechanical equipment associated with propulsion, braking, and air conditioning. There can be traction motor noise from electric motors used for propulsion in both electric and diesel locomotives. Then, there can be noise from compressors used in braking systems relying on air pressure for their operation, and noise from the discharge of an air brake. All propulsion systems, including railways require cooling fans, which can also be a major source of noise.

Another major source of noise mentioned by Technology for a Quieter America ¹ is the noise from a diesel engine, especially from its exhaust, and from its engine casing as well.

Horns, required at road and railway crossings to ensure sufficient warning, are also treated as a noise source by Technology for a Quieter America, ¹ especially in a residential area—the type of warning horn depends to a large extent on the policies and practices of the transit agency.

Studying the problem of high-speed railway noise

Ivanov et al. ² have studied the problem of noise from high-speed railways affecting the ecological safety of people living in the areas adjacent to the networks of the transport infrastructure. In their article, Ivanov et al. ² discuss the problems of noise control and prediction related to high-speed railway and devised calculation methods for determining such noise characteristics based on train speeds from 250 to 400 kmph, comparing their calculations with experimental results.

In their article, Ivanov et al. ² offer different ways of noise reduction, such as by installing small local noise barriers, and suggest aerodynamic streamlining of the rolling stock including its separate elements such as the pantograph. They claim their study has been implemented in several countries such as South Korea, Germany, France, Japan, and China, with good results.

Rail dampers reduce noise in rail networks

Since 1996, the University of Southampton ³ has been engaged in active research for reducing railway noise. Their efforts have been used successfully when expanding rail networks in Australia and Europe, while preserving the quality of life for people living nearby. They have a license agreement with Tata Steel for supplying patented rail dampers, and these have been fitted on railway tracks in 16 countries. In Sydney, these dampers have proven especially crucial for a new rail line.

According to the University of Southampton, ³ research work is being carried out at their Institute of Sound and Vibration (ISVR) under the guidance of Professor David Thompson. They are working on cutting down noise and vibration through new and economically viable solutions.

According to the research under University of Southampton, ³ wheels and track both are responsible for generating railway noise. They concentrated on reducing track noise, as there was no available practical method to do this, and they found several methods of reducing wheel noise.

Collaborating with Tata Steel, engineers from University of Southampton ³ were able to develop an innovative rail damper. The damper is made of steel embedded in rubber, and when attached directly to the rail, reduces noise by attenuating the vibrations the rail normally transmits.

According to ISVR, University of Southampton, ³ the development of dampers is a part of wider body of work on noise and vibration in railway networks. They claim the extent of noise reduction from rail dampers is up to 5–7 dB at the source, with the benefit-to-cost ratio reaching twice that obtained from using barriers. Apart from improving the quality of life for people living near railway lines, the effort from the University of Southampton ³ research has opened up a potential sustainable shift toward rail away from the more regular means of transport such as road, which is carbon-intensive.

Reducing noise with composite brake blocks

Clausen et al., ⁴ recognize railway noise as largely a problem of freight trains and trains containing older wagons and/or engines, with the severity of the problem increasing several fold at night. They claim poorly maintained rail vehicles and trains running on poorly maintained infrastructure produce greater rolling noise.

According to Clausen et al., ⁴ although passive measures such as insulating windows and noise protection walls are frequently used, they are only locally effective, while protecting wider parts of railway networks requires huge investments.

Rather, Clausen et al. ⁴ suggest widely introduced source-driven measures to lower noise across whole railway systems such as replacing cast-iron brake blocks with composite brake blocks in noisy rail freight cars. They also suggest use of wheel absorbers, aerodynamic design of pantographs, and noise-insulated traction equipment to reduce noise at source.

According to Clausen et al., ⁴ the current Technical Standard for Interoperability (TSI) Noise, requires lowering noise emissions by about 10 dB(A) for all rolling stock introduced since the year 2000, compared to those from 1960s and 1970s. This includes passenger power cars, passenger coaches, and engines.

Clausen et al. ⁴ claim a network-wide effect is only possible when noise is reduced ideally at the source. For this, they suggest retrofitting existing rail freight cars with composite K- or lower limit (LL)-brake blocks as the most cost-effective measure, although additional measures may be tried on the vehicle side, such as aerodynamically optimized pantographs, vehicle-mounted friction modifiers, and wheel absorbers.

However, Clausen et al. ⁴ do agree that the use of noise barriers or coverings cannot be avoided for reducing noise in densely populated environments and railway sections that are highly trafficked. They also claim that with wider introduction of vehicle-related measures, the number of covers or noise barriers can shrink significantly.

In their document, Clausen et al. ⁴ also list the actions several European countries are taking for noise abatement in railways.

Research projects involving implementation of traffic noise reduction

Oertli and Hübner ⁵ list several European and national research projects that study the implementation possibilities of traffic noise reduction in railways. Their selection of projects is as follows:

According to Oertli and Hübner, ⁵ a significant portion of rail noise can be eliminated if both track and wheel are smooth, as the roughness on both these surfaces in the contact area contributes to rolling noise. They claim a major cause of roughness on wheels is the result of the use of cast-iron brakes, and using composite brake blocks can allow the wheels to remain smooth.

Oertli and Hübner ⁵ recognize that braking is crucial for the safety of operations of railways. According to them, apart from braking performance, homologation procedures also consider safety and operating issues, especially performance under severe winter conditions and other effects on track circuits.

According to Oertli and Hübner, ⁵ although industry-developed K-blocks are homologated, and two LL-blocks have passed all safety tests, the latter show very high wheel and block wear.

Oertli and Hübner ⁵ are of the opinion that retrofitting has the best cost-benefit ratio. They base their conclusion on the comprehensive study of the STAIRRS project that summarizes the solutions using composite brake blocks as saving considerable amounts of money, as supported by studies undertaken in Switzerland, The Netherlands, France, and Germany.

Schulte-Werning et al. ⁶ describe low-noise railway, the noise reduction research program by the Deutsche Bahn (DB), of Germany. Their goal is to achieve a decline in overall noise production by about 10 dB(A) compared to 1990 for business units for freight and passenger traffic including infrastructure divisions.

According to Schulte-Werning et al., ⁶ for realizing the goal, DB is running seven parallel projects within its program. These are:

Schulte-Werning et al. ⁶ claim that DB is undertaking the major noise reduction program as an answer to public demand for low-noise railway traffic of the future. Various workgroups of DB experts are working along with acoustic professionals from other European railway undertakings and external institutions. However, the railway traffic situation in Germany is undergoing a change, as among other modifications, high-speed trains have come into operation. Existing guidelines can only tackle this situation insufficiently.

Lakušić and Ahac ⁷ have studied the effectiveness of noise and vibration mitigation measures applied to the network of European railway systems in detail in their research article.

In their research article, Lakušić and Ahac ⁷ study the noise and vibrations caused by traffic operating on tracks, as a part of analysis of rail traffic impact on the environment. They find both can be analyzed as a wave phenomenon, as noise propagates through the air, while vibrations travel through the ground, both in the form of waves. Both originate as vibrations of wheels and rails during vehicles rolling on track. According to Lakušić and Ahac, ⁷ vibrations occur in the frequency range 0–100 Hz and structure-born noise in the range of 30–2000 Hz.

Lakušić and Ahac ⁷ conclude that despite numerous researches, the effect of occurrence and propagation of rail traffic noise and vibration on people and rigid structures is still not fully understood, as the situation is very complex due to the involvement of a large number of influential parameters. They claim rail traffic noise and vibration problems are particularly prominent in cities with intense traffic mainly due to small distances between the tracks and the surrounding buildings.

According to Lakušić and Ahac, ⁷ they conclude that implementation and effectiveness of certain noise and vibration mitigation measures during the construction or reconstruction of modern rail and/or tram track provides significant improvements in terms of reducing the dynamic effects on the track.

Legislative and regulatory frameworks for limiting noise

SNCF Réseau ⁸ suggests a strict legislative and regulatory framework for limiting noise in railways. According to them, a section of the 1992 French law on noise specifically refers to railway noise and covers three main areas, as follows:

SNCF Réseau ⁸ determines the most appropriate acoustic protection on a case-by-case basis to comply with regulations. After consulting with residents, neighboring population, and elected officials, SNCF Réseau present these protection measures in the field.

SNCF Réseau ⁸ claim they have reduced noise between 7 and 10 dB(A) by taking action on rolling stock by replacing cast-iron brake blocks with those made of composite materials.

Conclusion

Governments and institutions all over the world are working toward improving the standard of life in the vicinity of railway lines by implementing several measures to reduce rail traffic noise and vibration, as rail is more environmentally friendly than most forms of transport, and they aim to expand sustainable public transport networks and increase passenger capacity.