Continue playing as if it were 1955

Every day millions of people face a deafening squeak. They do it every time They take the subwaya means of transport with many lights but with this great shadow. It is something that we live together almost without realizing: we have done everyday unbearable, but the question is: What is that noise?

Damn rolling. As he points out In the country Soledad Torres Guijarro, professor at the University of Vigo, the problem with the subway is the rolling, a noise whose origin comes “from the roughness of both the wheel and the raíl”. The problem has been studying for half a century, and affects both the subway and the railroad. Even the naughty ones that unite the rails “can be excited with those vibrations and become radiated elements.”

The tunnels do not help. While railroads circulate outdoors, the subway usually does it underground, inside a tunnel. That aggravates the situation because the tunnels are very reverberant spaces that amplify all the noises produced by the train. A study Made by Cecor in May 2022, it was concluded, yes, that “there is a small number of people exposed to noise levels greater than those marked” in official documents.

This plane shows noise levels in one of the areas covered by Metro line 5 in 2022. Source: Community of Madrid / Cecor.

Worse in curves. The squeak produced by the friction of the train tracks is aggravated in closed curves. That “howl” It is due to the lateral sliding of the wheels on the upper part of the railroad. There are other noises that add to those squeaks: the separation between the rails-to allow the thermal dilation of the metal-also causes the traditional “click-clac” sound when the subway cars pass over.

Rescue brakes. The problem has tried to mitigate with varied improvements. For example, they decreased by replacing Zapata brakes with the disk, this expert explained. The former rely on the wheel surface itself, but those of disco, much more silent, do not act against the contact surface.

And smaller wheels. Smaller wheels have also begun to be used, because the smaller the vibrant surface, the less capacity it has to generate sound. Even so, Torres stands out, roughness will always be there.

Other solutions. There is no unified response to the problem, but there are subway networks in which varied measures have been applied. In the New York Metro for example It was modified the way in which the tracks were fixed to the ground. The concrete naughty used there were covered with rubber to mitigate vibration, for example. In addition, panels were installed that absorb the noise on the ceiling and walls of the station, something that is complemented with the increasingly common protective acoustic screens – like those that were installed In the Biscay metro– installed close to the roads.

WHO recommendations. The World Health Organization (WHO) has specific recommendations for different noise sources. According to A document Updated in 2022, less than 54 decibels for noise caused by trains (44 decibels at night) are recommended. To try to mitigate the problem, the experts of this agency propose to “apply line rectified procedures to eliminate deformations and corrosion in the railways.” In a study on Hongkong Metro made in 2019 It was concluded that the average noise was 74.1 dB with 100.9 dB peaks.

BOE No. 178, of July 26, 2012.

And in Spain, what limits are there? In Spain, state reference regulations regarding environmental noise is the Law 37/2003, of November 17, of the noise (BOE No. 276, of November 18, 2003), and the Royal Decrees 1513/2005of December 16 (BOE No. 301, of December 17, 2005) and 1367/2007of October 19 (BOE No. 254, of October 23, 2007). The latter was updated with the Royal Decree 1038/2012of July 6 (BOE Nº 178, of July 26, 2012) with limits 5 dB higher than those of the previous document: the noise was not less, but more.

65 dB on residential soil. All of them transpose the 2002/49/CE European Directive, of June 25, on Evaluation and Management of Environmental Noise (DO No. 190, of July 18, 2002). In that last Royal Decree Annex III determines the limit values in rail and airport infrastructures, which fit what the Who points out although they do it depending on the type of soil: from day, up to 60 DBA for land of sanitary or teacher use (55 in the previous annex, for example), 65 dba for residential and 75 for industrial (50, 55 and 65 DBA at night, respectively).

Image | Ronnie Schmutz

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