Pass me the map

Measuring noise, part 8

We have now reached the point in our journey through the world of noise measurement where we understand what HS2 Ltd is telling us when it quotes a noise figure in dBA Leq, 18 hr. However, so far we have restricted our compass to a point that is twenty-five metres from the centre of the track over level ground; what we all want to know is what the noise will be around our houses. This will depend upon factors such as:

  • The distance that your house is from the track
  • The vertical alignment of the track relative to the surrounding terrain (e.g. is the track in a cutting or on an embankment)
  • Whether any noise barriers or noise bunds are employed
  • The heights of all points on the terrain between the track and your house (the path profile)
  • The nature of the vegetation in the vicinity and whether there are other man-made noise barriers, such as large buildings
  • Whether there are any bodies of water, or other reflecting or absorbing surfaces, in the vicinity

In addition to all of these factors the train is moving along the track, so there are an infinite number of noise source locations to take into account also; the highest noise level at your house may not arise when the train is at its nearest point to you.

This sounds like a job for a computer and, indeed, computer models are mercifully available to carry out the task. The most useful output from such a programme is a noise contour map and an example of such a map is reproduced below.

Sample noise contour map (source: CAA)

The example above is a portion of figure 11 from ERCD Report 1101 (here), prepared by the Civil Aviation Authority on behalf of the Department for Transport, and it shows noise contours at the western end of Heathrow airport.

The ERDC report also explains, in paragraph 1.1.3 on page 1, what noise contours are, as follows:

Noise exposure is depicted in the form of noise contours, i.e. lines joining places of constant Leq, akin to the height contours shown on geographical maps or isobars on a weather chart. In the UK, Leq noise contours are normally plotted at levels from 57 to 72 dBA, in 3 dB steps. The 57 dBA level denotes the approximate onset of significant community annoyance.

So if you are fortunate enough to live at the western end of Heathrow’s runways, all you have to do is find where you live on the noise contour map and work out the approximate dBA Leq level by interpolating from the nearest contour lines. Whilst you are looking at the Heathrow map please note that the highest contour around the end of the runway is 72 dBA Leq and remember this for future reference.

All you need then to work out how noisy HS2 will be where you live is a noise contour map for HS2 in your area. The problem is that no such maps have been provided by HS2 Ltd.

We were promised them. It’s in black and white in Hansard (here). Philip Hammond stood at the dispatch box in the House of Commons on 20th December last and said (Column 1203):

When the consultation is launched, I will also publish a revised business case, a full appraisal of sustainability, noise contour maps and route visualisations, all of which can be completed now that the final preferred route for consultation has been determined.

What HS2 Ltd has provided within the consultation documents package is a drawing series HS2-BZT-00-DR-SU-003-00 to HS2-BZT-00-DR-SU-003-42, which can be found in section 3.5 of Volume 2 of the Appraisal of Sustainability (which can be downloaded from here). These are described as “Residential Airborne Noise Appraisal Maps”; they are certainly not the promised noise contour maps.

I wrote to Alison Munro, Chief Executive of HS2 Ltd, on 12th April asking her how HS2 Ltd proposes to address this shortcoming. After reminding her at one of the recent roadshows that I had not had a reply, I have received a perfunctory “I have been asked to reply” letter, dated 16th June. This letter confirms that noise contour maps have not been calculated for the HS2 proposed route, to which I say: “Why not?”

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