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Preventing and reducing railway noise to protect quality of life

Railway noise is an important environmental and public health issue. Even more so because the population density along railway lines is high and that there is a strong demand for an alternative to road transport. SNCF Réseau is taking concrete measures on the existing railway network where the development of traffic and urban planning often go hand in hand. In addition, network modernisation and new line projects now include the acoustic dimension in early phases of project planning. The aim of this approach is to prevent the risk of disturbance and, if possible, to reduce it.
Mur en gabion multifonctionnel

Transport noise is the main source of quality of life disturbance for 54% of the French population (TNS-IFOP survey – May 2010 – The French Population and Noise Pollution – Ministry of the Environment). According to the results of the survey, transport noise is indicated by 7% of the respondents vs. 59% for road transport and 14% for airplanes.

Even though these figures show that the degree of disturbance resulting from railway transport seems to be limited, controlling railway noise is nevertheless important in order to be able to integrate the railway network as best as possible into the different living conditions of the population, and to meet the growing demand for public transport.

Where does railway noise come from?

Railway noise is produced both by the train track and the rolling stock. The noise is therefore a “railway system” issue. The origin of the noise depends on several factors and the impact of each factor varies according to the speed of the train:

  • The rolling noise comes from the interaction between the wheels and the train track, and the microscopic irregularities on their surfaces. At normal speeds this is the most common type of noise. In the railway station zone and when crossing metal bridges, other types of noise may be a disturbance.
  • Noise resulting from the traction power of the engines, ventilators and air conditioning mainly occurs when the train is moving at a low speed or when it is stopped.
  • Aerodynamic noise, due to the penetration of the train through the air, is especially perceived at speeds above 320 km/h.

Reducing the emission of noise therefore requires actions – sometimes combined – related to the rolling stock, infrastructure, train track and railway operations.

However, the reception of noise depends on how the sound is propagated between the point of origin of the noise and the receiving point (e.g. a home). This propagation is different depending on the distance, topography, presence or absence of natural or artificial obstacles, weather conditions, etc.

Reducing noise after it has been generated therefore requires actions – sometimes combined – related to the propagation path (e.g. barriers, landscaped shoulders) and the receiver (e.g. acoustic insulation of the building).

Quick facts to better understand noise
 
  • A variation of 2 dB(A) in noise level is barely perceptible by the human ear
  • The doubling of train traffic , with other things being equal, results in an increase of 3 dB(A)
  • An increase of 10 dB(A) generally corresponds to a sensation that the noise has doubled
  • With each doubling of the distance from a sound source, the noise level decreases by 4 dB (A)

A strict legislative and regulatory framework

The section of the 1992 law on noise, which specifically refers to railway noise (Articles L. 571-9 and10), covers three main areas:

  • Limiting noise along railway development projects for both new and existing lines, and requiring the project owner to comply with maximum noise levels during the day and at night (Articles R.571-44 to 52 of the Environmental Law Code).
  • Limiting noise during the construction of buildings along a noisy railway infrastructure (Articles R.571-32 to 43). The project owner of any new construction located in noise-restricted sectors (as defined by the relevant Prefecture) is required to ensure sufficient protection or insulation to limit noise levels inside the building.
  • Implementing a Noise Protection Upgrade and Noise Reduction Plan for critical situations and Noise Black Spots” (NBS). As part of this plan, infrastructure managers are required to map Noise Black Spot buildings and then to reduce noise levels through action plans. In addition to this plan, the European Directive on Environmental Noise (Dir 2002-49-CE) requires strategic noise mapping and noise prevention plans for the environment.

In compliance with regulations, SNCF Réseau determines the most appropriate acoustic protection on a case-by-case basis. These protection measures are then presented in the field in consultation with the residents, neighbouring population and elected officials.

Actions taken for the rolling stock have also been very efficient. Noise reduction has been estimated at between 7 and 10 dB(A). Cast-iron brake blocks are progressively being replaced by brake blocks made of composite materials. However, the transformation of the French rolling stock, and in particular freight trains, is progressing very slowly.

There are many ways to fight railway noise. The measures taken by SNCF Réseau focus on the origin of the problem in order to avoid the noise (sufficient distance from inhabited zones, lowering of the rail profile, installation of continuous welded rail – CWR, installation of concrete railway sleepers to reduce noise levels for neighbouring residents and in the environment in general). Measures also focus on the propagation path and include the installation of obstacles such as anti-noise screens and barriers. The sound insulation of facades is considered to be a last resort or complementary measure and is undertaken when no other solution is possible given the technical and financial conditions.
SNCF Réseau is implementing concrete measures to protect neighbouring residents against noise pollution.

Close-up of the Ile-de-France area
 

Noise pollution is a significant issue in the Ile-de-France area. Managing railway noise is made easier thanks to a two-tier governance structure which includes:

  • A Regional Committee of Railway Noise – its aim is to encourage exchanges and decision-making between the stakeholders.
  • A Technical Committee which includes the DRIEA (Regional and Interdepartmental Division of Equipment and Ile-de-France Urban Planning), Ile-de-France region, SNCF Réseau and SNCF Mobilités. This committee regularly meets to review the progress of ongoing operations and to prioritise action plans.

In addition, SNCF Réseau is a member of Bruitparif, a regional association which monitors environmental noise in the Ile-de-France area.

Priority action – reducing railway Noise Black Spots

A national plan for the reduction of railway Noise Black Spots (NBS) has been implemented for several years by the French State in conjunction with SNCF Réseau and its partners. The aim of this plan is to identify the most critical situations and to undertake treatment operations to reduce noise levels. The Grenelle Environmental Agreement reaffirmed this action to identify and reduce the most unhealthy noise black spots. This potentially involves about 58,000 buildings and 500,000 people.

Such actions represent a very significant budget. From 2008 to 2013 SNCF Réseau undertook to treat some of the most critical zones (primarily in the Ile-de-France, Rhône-Alpes, Aquitaine and Languedoc-Roussillon regions) for a total budget of € 140 million (including all types of financing). For example, approximately 1,200 NBS buildings were treated between 2008 and 2014. Some 18,350 people benefitted from these protection measures which represented the construction of more than 10,000 square linear metres of sound barriers.

In addition, SNCF Réseau is involved in innovation and research programs at both a national and European level: noise absorbers on rails, treatment of metal bridges, experiments to reduce vibrations, installation of low anti-noise barriers…

Noise levels at railway work sites – a national regulatory framework
 

When a project is subject to an impact assessment, the project owner must provide the following document to the department prefects and mayors of the towns in which railway works are planned: “Noise Management during the Railway Works”. This document summarises the key information about the railway works, the planned duration, expected noise disturbances and anti-noise measures. French regulations regarding “neighbourhood noise” define acceptable noise levels for the “normal operation” of work site equipment.

In the specifications for railway works, SNCF Réseau requires the use of approved equipment which complies with noise level standards. These rules apply to all work sites related to projects subject to an environmental impact study. The application of these rules for renewal and maintenance work sites is voluntary, in particular for densely populated urban areas.