A step in the right direction

I mentioned in my blog Here comes more work (posted 3 May 2012) that I had found a surprise in the draft of HS2 London to West Midlands EIA Scope and Methodology Report (here); after trying to convince us in the Appraisal of Sustainability (AoS) that night noise from HS2 wasn’t worth bothering about, HS2 Ltd now appears to appreciate that it might be a problem.

In my blog Nessun dorma(posted 7 Dec 2011), I pointed out that the AoS had completely ignored the recommendations of the World Health Organisation (WHO) document Night Noise Guidelines for Europe (here). Well it now appears that the acousticians working for HS2 Ltd have found a copy, dusted it off and realised that they ought to pay attention to it.

In Nessun dorma I explained that the WHO had recommended a night-time noise threshold, identified as the night noise guideline (NNG), together with a higher-level interim target (IT) for “situations where the achievement of NNG is not feasible in the short run”. It would appear that HS2 Ltd has adopted the NNG, which is specified as 40 dB(A) equivalent continuous sound level over the eight night hours, as the threshold for night-time noise in HS2 London to West Midlands EIA Scope and Methodology Report.

The way of applying this threshold is a little convoluted. It is set out in paragraphs 13.3.24 and 13.3.25 on page 119 of HS2 London to West Midlands EIA Scope and Methodology Report. In order to record a “noise impact” at a receptor the forecast HS2 noise must cause “a change in the equivalent continuous sound level between 23:00 and 07:00 of 3 dB or greater” and that increased equivalent continuous sound level must exceed the NNG level of 40 dB(A).

Now it shames me to admit it, but over the last couple of years I’ve learnt a healthy scepticism when dealing with HS2 Ltd. However, I have thought about this proposal carefully and can’t find the catch; maybe someone cleverer than me can spot one. It is basically the same way the AoS used the daytime 50 dB(A) threshold that marked the bottom of the “grey dot” band. Whilst I have a problem with this daytime threshold being inconsistent with the assumption that existing noise levels in tranquil areas is 45 dB(A) (refer to my blog That’s a bit of an understatement, which was posted 5 Nov 2011), I have no quarrel, I think, with the application of the “3 dB change” criterion.

By the way, paragraph 13.3.25 also confirms that this 50 dB(A) threshold, together with the 3 dB change requirement, has been retained as the daytime threshold for the HS2 London to West Midlands EIA Scope and Methodology Report.

But I digress; getting back to this new night-time threshold, because of the “3 dB increase criterion” the existing night noise equivalent continuous sound level must not exceed 37 dB(A) for the 40 dB(A) threshold to apply. This is because for every dB that the existing night noise equivalent continuous sound level exceeds 37 dB(A), the 40 dB(A) threshold will increase by 1 dB(A). So if the existing noise level is 40 dB(A), the night noise will not be recorded as a “noise impact” unless it exceeds 43 dB(A).

What this calculation process means is that the adoption of the WHO NNG for the EIA process will have most impact in areas where the nights are relatively tranquil at present; presumably this will be predominantly rural areas where there are no existing transport corridors. It is also more likely that the threshold will be exceeded in track sections where the trains are running at maximum speed. Since this description fits the vast majority of the route from the Chilterns up to Warwickshire and even the rural parts of the West Midlands, the adoption of this new threshold may influence the number of “noise impacts” that HS2 clocks up; or put more simply it may increase the count of properties that are affected by noise.

In the next blog I shall try and get some idea of how large this increase might be.


2 responses to this post.

  1. Posted by Bill Adam on May 7, 2012 at 10:46 am


    Have you tried offering HS2 an alternative?

    I offered Lord Adonis (in his time) the possibility of building on the fast lane of the M40 with its reduced cost and reduced environmental damage. (It was heard but rejected.

    Can you see a major snag with my suggestion to bury the rail line? (Dig a trench 10 metres deep and 4 metres wide, put the outward line at the bottom with the inward line above it then cover with soil.) The line would make these noise level problems irrelevant. There would be no” leaves on the track” problems, or snow, or fog. Any additional cost could be offset against improved service and the reduced cost of inquiries, consultations and delays.

    Bill Adam


    • Hi Bill. The only official interface that I have with HS2 Ltd is the Offchurch and Cubbington Community Forum. Any discussion of alternatives to the consulted route is strictly off limits to this forum, other than design changes offering possible mitigation; in practice this means changing the vertical alignment (maybe) and adding mitigation features, such as barriers and bunds. Any request to change the horizontal alignment would, I think, be ruled out.

      I’m afraid that the reality is that any radical modifications, of the sort that you are proposing, would be a total non-starter. Remember that late last year the Labour Party Front Bench suggested that the route should be changed to go through a Heathrow Hub and that proposal was unceremoniously batted away by the Transport Secretary.


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