Useful underground noise computation

Open Data
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There have been a number of articles in the press about the sound levels on London Underground. Usefully the Economist managed to provide a useful graph of measurement, thus

image

However, whilst the diagrams show (in heavy highlight colour) the problem sound area, the article simply highlights the peak level between stations, and this isn’t the real issue when it comes to Health and Safety.

So, I propose each inter-station link has a value z, which is the decibel-minutes of excess noise.

zdbAmin=t=0t=TLmax-85060
z space d b A m i n equals fraction numerator sum from t equals 0 to t equals T of open parentheses open parentheses L subscript m a x end subscript minus 85 close parentheses greater or equal than 0 close parentheses over denominator 60 end fraction1514×301 16.5 KB

Lmax is defined in ISO 17025 as the max value of Leq for each second interval.

85dbA is the “safe limit” taken from http://www.hse.gov.uk/noise/noise.pdf

The use of minutes means that the results will be usable integers, rather than hundreds.

Any journey where the level never exceeds 85dbA will get z=0

A 300 seconds at 90dBA will get z=25
A 60 seconds at 115dbA would be z=30

For fairness the measurements should be taken in the centre carriage at 1 meter about the floor. The main issue I have with data collection is finding calibrated equipment, as the apps out there don’t have an external reference. Any ideas?

The articles were:

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I’ve got some data now! I would be more than happy to share it.

Of course I have made a colour coded tube map, with per-link colouring. There are over 140 data points used for this map.

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TfL measired traom noise levels version 1.0.png2813×1974 623 KB

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The quietest links I found were

image
image.png800×367 32.6 KB

And the loudest I found

image
image.png781×405 39.6 KB

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@briantist - Amazing work! I’ve passed your posts on to a few of my colleagues in case they are interested. Thank you so much for sharing this on the Tech Forum!

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@theochapple

A neat trick would be for them to use the information from the first chart to control exactly where in the tunnel to play announcements. At the moment, announcements are frequently played when the noise is at its loudest, rendering them totally inaudible. But presumably some kind of beacon or marker could be installed in the tunnel to trigger the announcements at an optimum point.

Talking of announcements, does the driver hear them? I once boarded an overground train which was bound for Chingford according to signs and announcements at Liverpool Street but the announcements on the train itself said it was for Enfield Town. I assumed the driver would notice and correct it once the train passed Hackney Downs where the lines split and it should have been clear that the train had stopped at a station that was different to the one mentioned in the spoken announcements. But it continued giving incorrect announcements right up to Chingford and at that point I noticed that even the front of the train said Enfield Town.

So, it seems that despite Overground trains promising, and generally having, staff at every station, not one of them noticed that front of the train said something different to the signs and announcements on the platform. They should surely have alerted the driver to have it checked :upside_down_face:

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