Check made: only 75 decibels for a tramway?

AFFIRMATION: “The Sun recently cited an expert report commissioned by the City of Quebec, which ensured that” the noise emitted by a streetcar is 75 decibels, while that of a bus reaches 75 to 80 decibels and a car, 80 decibels “. But I will not be led to believe that a streetcar with metal wheels rubbing on metal rails is quieter than a car. It seems all the more suspicious to me that the article also says that “the parameter retained in the industry is the equivalent sound level over a long period and not the event”. Does this mean that the tramway and its screeches are drowned in the average? What is the true noise level of a streetcar? “Asks Serge Trépanier of Québec City.
FACTS

The report in question is the work of the engineering firm Systra, a multinational specialized in transport and which therefore has a priori all the necessary expertise. In his PowerPoint presentation , Systra made it clear that the passage of a tram produced a noise of 75 decibels (dBA) at 10 meters distance, while a car would be at 80 dBA. The report itself speaks instead of 78 dBA at 7.5 m (on page 3) for a streetcar.

In this kind of material, the concrete conditions of measurement (type of tram, kind of rails, configuration of the place, etc.) can make a big difference, but everything indicates that Systra has retained a reasonable noise level for the passage a tramway. A 2009 French report bit.ly/2DHNG1D , p. 54], for example, measured the noise of the Nantes tramway in two places, achieving maximum sound levels of 70 to 80 dBA at 7.5 m distance when the tram was traveling at 40 km / h – note here that the speed can make a big difference. A Slovak study published in 2016 in the scholarly magazine Noise & Health for its part found around 75 dBA at 7.5 m for speeds of about 25 km / h.

There are two things to add here about Systra’s report. The first is that the document did indeed take into account the metallic creaking that trams often produce in curves. The authors have in fact added eight decibels to their estimates “in low radius curves to simulate squeal noise, in accordance with the guidelines of the European calculation method, CNOSSOS-EU” (p.3). Verification done, this is indeed the European recommendation for estimating noise in curves of less than 300 meters radius bit.ly/34LkRNT , p. 57 of 180]. In this respect, according to the Slovakian study of 2016, the squeal makes an average difference of 9.5 dB on the noise of a tram, which is compatible with the 8 dBA adjustment retained by Systra.

The second thing to know is that the Systra report assumes that noise reduction measures will be taken, such as the construction of noise barriers in some areas or a rail lubrication system to mitigate squeaks (which would then go from + 8 dBA to + 3 dBA). This is not necessarily a far-fetched presumption, let us emphasize it, since it is difficult to see Quebec’s interest in indisposing residents if it can be avoided at low cost. But it is nevertheless what allows the report to draw conclusions very reassuring: the tramway would increase the level of ambient noise for the riverside houses that on 5% of the route. Without these mitigation measures, half of the route would experience increased noise pollution.

Anyway, however, it remains that all the points of comparison that I could find point in the same direction: the noise level estimated by Systra seems quite realistic.

If there is one thing that is perhaps a little less, in this story, it is the noise level of cars that, at 80 dBA, provides a flattering comparison point for the tram. But it seems a little too high. For example, in an impact study on a gold mine project, the ERM consulting firm talks about “60 to 80 dBA” for a car that would be 10 meters away . Similarly, a noise level scale on the site of the Danish Environmental Protection Agency indicates around 70-75 dBA.

So we must conclude that these 80 dBA do not correspond to the typical noise of a car, but rather to the noisiest models. Which, of course, then makes the streetcar appear quieter than it really is.

THE VERDICT

True in the whole. The 75 dBAs that Systra and the City of Quebec have identified as “typical noise” of a streetcar match well with all the external points of comparison that I could find. In addition, the firm has indeed taken into account (in the rules of the art) squeal noises in the curves. It seems, however, that the comparison with cars at 80 dBA is artificially flattering for the tramway.

+

INFO TO CHECK?

The statement of a minister seems doubtful to you? Circulating information seems exaggerated, unfounded? Write to our reporter ( jfcliche@lesoleil.com ). The section “Verification made” will take the time to delve into the facts, in depth, to give you the right time. Because we either do not like false news.

Share Button