NOISE REDUCTION
- an Environment Protection Issue at the Railways -

The XXth century has been named the "century of speed" due to the rapidity of the development of the society in all the fields, but also referring to the direct increase of the traffic speed of people on the ground, on the water, on the air and even in the interplanetary space. The XXIst century has great chances to be called the "century of the environment protection", because people pay a bigger and bigger attention to the protection of the planet they are living on, Terra, starting to show tired.

Today, more than ever, it has become extremely compulsory that in the process of elaboration of a new project in almost every field of activity to be taken into account, first of all, the achievement of certain studies showing the effects of the respective project on the environment.
Especially when it is about the various types of transport the environment protection issues represent an extremely hot aspect. The society has become aware in the last years of the negative consequences that the transports have on the entire environment. That's why they use all the levers that they have available in order to influence the constructors and the operators of this field to involve more actively in the environment protection process, in saving the Blue Planet.
As a reply to this new imperative, yet since the beginning of the '90s, the International Union of the Railways (UIC) has decided to grant to the environment protection a strategic importance in the policy promoted by it in the development of the railway transport. On this purpose, there has been created a special working group, reuniting specialists from all over the world who are looking for solutions for the reduction of the energy consumption, of the noise, of the vibrations, of the noxious emissions - by promoting, among others, the electrification of the operated railway sections - and, not at last, for the awareness of the decision factors, as well as of the entire society on the fact that, by its reduced polluting level, the railways represent the wisest option for the future in point of terrestrial transport.
The recommendations made by UIC in this respect are applied by the profile companies, among which CFR SA. The measures taken by the companies lately testify its interest to own not only a performant infrastructure from all points of view, as well as less a polluting one.
Therefore, the projects for the modernization and rehabilitation works of our railway infrastructure are based on the studies performed to demonstrate the impact on the environment, which are submitted to the public debates of the communities that are in the affected area. One of the elements closely aimed in these studies is the reduction of the noise level.
The noise level of the trains, the railway noise and of other means of transportation are expressed in terms of level of continuous constant equivalent noise - Leq.
Leq,t is the level of a constant noise in time, which, for a given position and on a definite period of time T, has the same balanced acoustic energy A, as the existing fluctuant noise.
The balanced level A is used for all the noise evaluations; the measure unit is dB(A).
The balanced noise levels are the levels of acoustic pressure that have been adjusted taking into consideration the fact that human hearing is not the same in point of sensitivity for all the frequencies.
In order to measure the level of acoustic pressure (Lp) there are used translators sensitive to the pressure (usually, microphones). The Lp level is expressed in decibels (dB) and is calculated according to the formula:
Lp = 10 x lg x (p˛/p0), expressed in dB,
where:
p = the acoustic pressure of the measured noise;
p0 = the reference acoustic pressure (2 x 10-5 Pa).
According to the legislation in force, the "health" state of the environment from the acoustic point of view in the area of an objective is established by STAS 10009 - 88, Urban Acoustic - the admitted limits of the noise level. In this normative paper it is stipulated that to the limit of an industrial precinct the maximal value of the noise to be of 65 dB (A), and according to ATAS 6161/1-79 in the location of the living buildings should be provided an inferior value of the maximal one, of 50 dB(A), for the level of the noise outside the building, measured at 2 m in front of it. Generally, the legislation of the European countries stipulate limits of almost 50 dB(A). In the field of the railway transport the sound pollution comes from:
- the so-called activity of railway transport (by the noise produced by the wagons operation and of the locomotives and the acoustic signaling);
- the activity of the locomotives depots;
- the activity of the railway stations.
The train has a structure that allows a wide range of noises and vibrations, which have the roots the mechanical and electromechanical nature phenomena. In order to provide the comfort of the passengers, of the railway personnel and of the population that lives in the neighborhood of the railway stations, of the depots and of the railway tracks there is imposed that the level of the noise and of the vibrations to be as reduced as possible.
There have been identified the following sources:
- the noise determined by the wagons operation, which occurs as a result of the vibrations and the shocks of the various components of the wagons (rolling elements, braking clogs etc.). At the train operation with 70-80 km/h on the tracks assembled on reinforced concrete slippers the level of the noise can reach 125-130 dB(A), the most intense being the one caused by the wheels collision with non-uniformity of the track and of the joints. This type of noise is propagated on big distances along the railway axle. It can be diminished by reducing the wear of the track dimpling, by achieving railways without joints and by assembling certain rubber gaskets between the sole of the track and the slipper. This way, the noise level is reduced 2 - 2.5 times;
- the noise of the locomotives - occurs during the operation of the trains, the acoustic level being increased with 6-7 dB(A) in comparison with the one recorded during the stops. The main source of noise at the electrical locomotives and also at the Diesel locomotives is the engine, which, due to the conditions imposed by the gauge, can not be completely close in a sound-insulating carcass;
- the noise of the railway stations, which is influenced by the volume of traffic, by the degree of the technical endowment and by the power of the means of hauling that are operational in the railway stations and in the marshaling yards. At the departure and at the arrival of the trains, the operation speed does not exceed 30-40 km/h, the level of the noise recorded at the 100 km distance against the railway axle being in average of 65-75 dB(A), also reaching up to 90 dB(A) in the most crowded areas of the station; the noise with high frequencies occur especially while the locomotives are passing by. In the marshaling yards stations, the most upsetting are the noises that are caused by the braking process and by the wagons plugging, to which there are also added the squeaking in curves, the operation of the engines and the air blowers from the locomotives, the drawing out of the wagons from the preparation platform to the marshaling yard hump and the operation of the intercommunication systems through the loudspeakers;
- the acoustic signaling from the railway stations - represent a secondary source of acoustic discomfort. The situation is more delicate: for the operators the signals should be heard and received without errors from a distance as big as possible, yet, in the same time, for the inhabitants from the neighborhood they should have an acceptable intensity.
The railway noise differs from the road traffic by the following:
- by the temporary frequency of the noise, which in case of the trains is regulated (the increase of the landing, the decrease of the sound level), this one being different from a train to another and according to its length;
- the source is well localized in space (the train is a guided mean of transportation).
While performing the assessment studies for the sound levels in the neighborhood of the railways there are usually taken into account the most unprivileged situation for the environment: the traffic debit for a day with maximal traffic and the propagation of the noise in the conditions of plane and of reflecting soil.

These studies have demonstrated that in case of modernizing the railway sections that are crossing the inhabited areas it proves to be more efficient the adoption of certain anti-noise measures yet from the designing stage for the modernization, because it implies much reduced costs. In order to protect the fragile ecosystems there can be taken additional measures, as well as the creation of the ecological barriers and the building of certain new types of tracks.
The starting off of the rehabilitation project for the pan-European Corridor IV on Bucharest - Campina section, it re[resents a premier for the Romanian Railways, and the way in which there are developed all the working stages - starting with the organization of the auctions to the drawing up of the studies, from the organization of the works up to the performances of the machines that are used - already represent a standard for the future projects.
Among the studies achieved on this occasion there is also a preliminary study dealing the impact on the environment, which, besides the public debates, has aimed the awareness of the way in which the community perceives this project. The four aspects aimed by the questions that the subjects had to answer have been: the degree of absolute and relative preference of the means of transportation used and the frequency of using it; the reporting to the sound pollution effects and to the discomfort inducted by the railway traffic; the impact of informing through media of the ISPCF project and the direct perception (by reporting to the appreciation on the travelling conditions).
The results of the Gallup poll have showed that the great majority of the population that have been questioned consider that travelling on the railways corresponds to their transport preferences (opinion shared by almost 44% of the ones that have been questioned in Busteni railway station and 38% among the ones questioned in the train). Moreover, over 71% of the passengers have said that they prefer travelling by the train than the other means of transportation. With respect to the quality of the services that they are taken advantage travelling by the train, 85% have stated that they prefer to be increased the level of comfort in the train, then they have opted for a higher speed during traffic ((65%), and thirdly, to have arranged the railway stations (almost 50%). Among the main deficiencies recorded in the passengers' transport the noise is situated on the fifth place, after the discomfort, increased costs, decreased speed of operation and the arrangement of the railway stations.
The impact produced by the noise resulted from the railway transport activity is much more powerful during the development of the rehabilitation and modernization works, case in which the usual noise produced by the train passing by is added the one specific to the site. That's why, for diminishing the sound pollution there have been adopted certain measures successfully used in other countries - the assembling, during the unfolding of the works, in the sensitive areas (with the houses located in the proximity of the working sections), of certain sound-absorbing panels. The international experience has demonstrated that, this way, for the houses placed at less than 50 m from the railways the intensity of the noise can be reduced with almost 50%. But also the expertise shows that these panels are very expensive and, additionally, they represent visual obstacles.
Along the time, for the reduction of the noise on the railways there have been made various studies, there have been adopted a multitude of solutions, according to the needs and the possibilities of various companies or infrastructures. From the assembling of the anti-noise panels along the railway track, to the decrease of the wheels and tracks irregularities, from the implementation of the braking clogs made of composite materials for the freight wagons to the implementation of new types of track etc., etc., etc., all these solutions testify the restless concern of the railway personnel to make the "voice of the train wheels" to become only a …metaphor.

Sivila Mirea
Aurora Smarandescu