Checking the shopping list

This article was first published on HS2 and the Environment.

A couple of months ago HS2 Ltd staged one of its friendly purchaser/supplier get-together events for potential manufacturers of its fleet of high-speed trains and those rail industry members, and others, who might be interested on the periphery. As one might have expected, the prospect of £billions being cast upon the rail industry’s waters (see footnote 1) was, to thoroughly mix the metaphors, a honey pot that attracted the flies in swarms – the attendance list identifies two hundred and fifty organisations with delegates present.

A few weeks after this monumental shindig was held HS2 Ltd published a Pre-qualification Technical Summary for the HS2 rolling stock (PQTS). This is an outline specification that contains, we are told, “the requirements considered material to bidders”: presumably the intention is that potential bidders will use the document to determine if they will be able to offer equipment that will fit the bill and, accordingly, come to a decision about whether to subject their organisation to the rigours of the pre-qualification process. So, although we can’t expect that all of the i’s have been dotted and the t’s crossed in this document, it should, at least, provide an indication of the direction in which HS2 Ltd’s corporate thoughts are heading.

As anybody will know who is at all familiar with the soul-bearing exercise that I have been engaged in on this site for six years now, I have a bit of an obsession with the impacts that the noise generated by HS2 trains will have, so I was interested to see what provisions for mitigating this noise at source have been included in the PQTS.

The train operational noise calculations presented in Appendix 5 of the Phase 1 Environmental Statement were made based upon the assumption that trains supplied for the HS2 project, both “captive” and “classic-compatible” designs, will be “specified to be quieter than the relevant current European Union requirements”. The magnitude of this assumed noise reduction is stated to be “approximately 3 dB at 360kph compared to a current European high speed train operating on the new track” (see footnote 2).

I am pleased to confirm that this assumption has been recognised in the PQTS, albeit not yet in strict terms. Potential tenderers are advised that the train pass-by noise limit (the “Contractual Pass-by Limit”), which is yet to be set, will not be greater than “that specified in the NOI TSI (see footnote 3). Further, tenderers are advised of the 3dB reduction that has been assumed for the Environmental Statement, the legal requirement for HS2 Ltd to “take all reasonable steps not to exceed the airborne noise levels predicted in the HS2 Phase One Environmental Statement” and the consequent expectation that HS2 Ltd will “invite Tenderers to propose Contractual Pass-by Limits that are lower than that specified in the NOI TSI”. Also, potential tenderers are given the added incentive of being awarded a reduction in the value assessed for the whole-life cost of their solution for each decibel that the pass-by noise is below the NOI TSI limit (see footnote 4).

So, as with so many other aspects of HS2, what the PQTS is offering us falls somewhat short of a cast-iron guarantee, but we do have an indication of intent to meet the airborne operational noise predictions that are set out in the Environmental Statement (ES).

But the operational airborne noise predictions are not solely dependent upon the magnitude of the total noise radiated by a passing train. This is because points all over the body of the train, from the very bottom where the wheels have contact with the rails to the very top where the pantograph rubs against the power catenary wire, will contribute to this total noise, and the extent that each of those points propagate that noise and contribute to the aggregate noise experienced at any receptor will depend upon the height of the point above track level. This height dependence affects both the propagation over the natural terrain and the efficiency of any artificial noise barriers assumed for the calculations in the ES, be they bunds or fence barriers.

The computer model that was employed to make the ES predictions takes account of this height dependence by approximating the umpteen sources all over the train body to five effective sources at heights above rail head of 0.0, 0.5, 2.0, 4.0 and 5.0 metres (see footnote 5). Equations expressing the relationship of each of these five sources to the speed of the train have been identified in the ES, and these relationships allow the noise levels emanating from each of the five effective sources to be calculated at any speed (see footnote 6).

As long ago as 2011 I was expressing concern about the assumptions that HS2 Ltd was making for the noise generated at the higher levels on the train, resulting from aerodynamic effects (see footnote 7). It is a subject that I have returned to on a number of occasions since, and which I dealt with in considerable detail in a series under the sub-title Impacts of aerodynamic noise on noise mitigation efficiency that I posted towards the end of 2012 (see footnote 8).

Artists impression of HS2 Ltd undertaking noise assessment work.

On the evidence that I cited in the Impacts of aerodynamic noise on noise mitigation efficiency series, there is fairly general agreement that the contribution made by the pantograph to overall pass-by noise can be significant. In the ES, however, the assumption has been made that pantograph noise at 360kph will be, with the exception of the noise coming from the train power, traction and auxiliary systems, the quietest noise source, and at 12dB below the total noise predicted, will have, in the absence of any noise barriers or bunds, an insignificant impact upon that total noise (see footnote 9). This assumption relies on the belief that a reduction of at least 10dB below the levels of noise generated by “a traditional European HS pantograph” can be achieved if a “more aerodynamic” design is employed, adopting the low-noise pantograph design techniques that have been developed in Japan (see footnote 10).

In spite of the inclusion of a low-noise pantograph in the HS2 rolling stock design specification apparently being essential to realise the predictions made in the ES, particularly where barriers and bunds have been employed for noise mitigation, the PQTS is remarkably reluctant to press home the need. The section in the document covering pantographs (see footnote 11) makes no mention of a low-noise design being required and the section on noise merely tells the potential tenderer that “HS2 Ltd is considering how and whether to specify requirements for high-level noise emanating from [the] roof area of the train, including the pantograph” (see footnote 12).

The published script for the presentation that Tom Williamson, Head of Rolling Stock Engineering at HS2 Ltd, gave to the assembled masses at the launch confirms that he admitted that “aerodynamic noise becomes a real problem above 300km/h and noise from higher up on the train doesn’t tend to be contained by noise barriers” and that he referred to “the low-noise pantograph solution … from Japan”. He also dropped a bit of bombshell regarding the classic-compatible train design – a potential problem that I have not seen referred to before in any HS2 Ltd documentation – that “the constrained gauge of the conventional compatible trains makes straightforward adoption of [the Japanese design] difficult” (see footnote 13).

It strikes me that close scrutiny of how this procurement process develops will be necessary to ensure that HS2 Ltd does not submit those on the route to higher levels of noise pollution than it has so far indicated will be the case.


  1. Although the surety of receiving a harvest of reward implicit in Ecclesiastes 11:1 can hardly be claimed with certainty for HS2.
  2. See paragraphs 1.2.16 and 1.2.17 in Annex D2 to Appendix SV-001-000 Methodology, assumptions and assessment (route-wide): Sound, noise and vibration, Volume 5 Technical Appendices London-West Midlands Environmental Statement, HS2 Ltd/Department for Transport, November 2013.
  3. The “NOI TSI” is the EU noise specification that has superseded the rolling stock TSI that was in force at the time that the Environmental Statement was being written (2008/232/EC). It is set out in the Annex to the document Commission Regulation 1304/2014 of 26thNovember 2014 concerning the technical specification for interoperability relating to the subsystem ‘rolling stock — noise’ amending Decision 2008/232/EC and repealing Decision 2011/229/EU, Official Journal of the European Union, 12th December 2014.
  4. See paragraph 7.18.1 in document reference HS2-HS2-RR-SPE-00000006, Pre-Qualification Technical Summary, HS2 Ltd, 21stApril 2017.
  5. See paragraph 1.1.27 in Annex D2 to Appendix SV-001-000.
  6. See paragraphs 1.1.28 to 1.1.30 in Annex D2 to Appendix SV-001-000.
  7. For example, see my blog Going over the top (posted 9 Nov 2011).
  8. The individual blogs in the series are Are you taking this seriously? (posted 27 Nov 2012), What do they know? (posted 1 Dec 2012), It’s there for all to see (posted 5 Dec 2012), Or putting it another way (posted 9 Dec 2012), I can hear you (posted 13 Dec 2012) and Being a bit hopeful? (posted 17 Dec 2012).
  9. See Figure 5 in Annex D2 to Appendix SV-001-000.
  10. See paragraph 1.1.40 in Annex D2 to Appendix SV-001-000.
  11. Paragraph 7.5.2 in document reference HS2-HS2-RR-SPE-00000006.
  12. See paragraph 7.18.1 in document reference HS2-HS2-RR-SPE-00000006.
  13. See page 46 of the presentation script HS2 rolling stock: scope and requirements presentation, HS2 Ltd, 28thMarch 2017.
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