Some Facts about Sound Levels

Over the days leading up to and around Christmas there have been several posts in the Baie-D’Urfé Facebook Group about the perennial issues of sound levels from the highway and rail tracks. Citizen Marat thought it would be time for some hard data …

This consisted of a preliminary expedition to take a few sample noise levels in the north-western part of the town in mid-afternoon on Boxing Day; a day one might reasonable anticipate to be one of the quietest of the year. What follows is preliminary data only, but we think instructive. More sampling will be done in the weeks ahead.

Noise levels were collected using a simply protocol (stand still and point microphone towards the highway 😉 ) with the “Decibel X” app for iPhone. Decibel X is a highly rated app for this purpose, you will find reviews on the internet. Quote: This highly-rated app turns your smartphone into a pre-calibrated, accurate and easily portable sound level meter. It has a standard measurement range from 30 to 130 dB. It boasts many features for measuring the intensity of sound around you built into a nicely-designed, intuitive user interface. Also: “Decibel X” is one of very few noise meter apps on the market that has highly reliable, pre-calibrated measurements and supports dBA, dBC. It turns your iOS device into a professional sound level meter, precisely measures the sound pressure level (SPL) all around you.  

NOTE: This is not a professional sound metering system, it is however highly indicative of real-life experience and more than adequate for the purposes of this experiment. (** HOWEVER – we have now been offered use of a professional sound meter and so will take this exercise further during January 🙂 )

Measurements were taken at around 15h00 on Wednesday 26 December 2018 at four sites shown on the following map.

  • Site 1 – St-Andrews almost 1200 feet / 8 houses distance from the highway (measured on Google map)
  • Site 2 – St-Andrews separated from the highway by a narrow strip of trees. Conveniently a train was passing when this measurement was taken.
  • Site 3 – Western part of Surrey separated from the highway by the widest strip of natural woodland in the town. Approximate width 200 feet (measured on Google map). A wooded area of 100 feet width has been estimated to reduce sound levels by around 5dB. Highway traffic only.
  • Site 4 – Middle of John-Weir Park

Results/Data

Site 1

The measurement was taken 1200 feet from the southern edge of the highway at about 8 properties from the house closest to the highway. There was no passing traffic on St-Andrews at the time, all traffic noise came from the highway.

Average sound level was 70dB with a minimum of 58.7dB and a maximum of 77.2db over a time period of 25 seconds.

Note: a train was approaching but was not passing while this measurement was taken. It is estimated that the train was no closer than the John-Abbot Campus.

Site 2

Measured at the top of St-Andrews at a level with the nearest houses to the highway. A train was passing at the time. It is worth mentioning that the ambient noise level while the train passed was such that conversation was difficult.

Average sound level of 77.3dB with minimum 71.4dB, maximum 81.1dB and a single peak of 85.8dB over a 53 second period.

Site 3

Measured on Surrey separated from the highway by a belt of trees about 200 feet deep. The train had passed and all noise was from the highway.

Average sound level of 67dB with minimum 61.8dB, maximum 80.6dB over a period of 40 seconds.

It is inferred from these data together with those from sites 1 and 2 that the strip of woodland separating the sampling site from the highway is sufficient to attenuate the sound as measured in front of the nearest houses to some degree. The reduction could be as much 10dB but more data points are required before this can be conclusively demonstrated.

Site 4

A final sample was taken in the middle of John Weir Park. Again, main noise source was highway traffic. As anticipated this was the quietest site and the noise levels were closer those of the WHO recommendations (q.v.)

Average sound level of 54.7dB with minimum 50.4dB, maximum 67.3dB over a period of 37 seconds.

Implications

** The WHO recommends that for a healthy environment the traffic noise level should not exceed 53dB during the day or 45 dB at night.

Daytime average noise levels in this single sampling exercise on a “quiet” day with low traffic flow were observed to be well above these recommended levels and very markedly above when a train is passing. The presence of a belt of trees 200 feet deep does seem to provide a degree of sound attenuation.

This is no more than a sample exercise and not intended to be a foundation for policy development. Nevertheless, it is indicative of exceptionally high noise levels in a real-world situation. It is intended to expand on this initial exercise and collect more data from various point sin the town using a standardised measurement protocol and under different environmental conditions. It is hoped that these data will be helpful to citizens affected by traffic/rail noise in their environment.

It is pleasing to see that funds have been allocated by Council for stage 1 of 4 of the installation of sound mitigation measures (berm/wall). Many people will be interested to learn from Council what sound level attenuation is anticipated to result from whatever solution is finally approved and installed.


WHO Recommendations

The World Health Organisation recommend the following standards for noise from road traffic (quote):

For average noise exposure, the GDG strongly recommends reducing noise levels produced by road traffic below 53 dB L den , as road traffic noise above this level is associated with adverse health effects.

For night noise exposure, the GDG strongly recommends reducing noise levels produced by road traffic during night time below 45 dB L night , as road traffic noise above this level is associated with adverse effects on sleep.

To reduce health effects, the GDG strongly recommends that policy-makers implement suitable measures to reduce noise exposure from road traffic in the population exposed to levels above the guideline values for average and night noise exposure. For specific interventions, the GDG recommends reducing noise both at the source and on the route between the source and the affected population by changes in infrastructure.

Environmental Noise Guidelines (2018) World Health Organisation

The full report can be consulted at this link:

http://www.euro.who.int/__data/assets/pdf_file/0008/383921/noise-guidelines-eng.pdf?ua=1

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