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Your questions answered: High Speed 2

Our panel of experts respond to your queries on the contentious plans to update Britain’s rail network with a new high-speed line.

The planned high-speed rail network linking London with the north of England (HS2) is probably the most controversial engineering project in the UK today. Proponents say it will ease overcrowding on existing lines and encourage investment and economic growth by effectively bringing Manchester, Leeds and Birmingham closer to the capital with shorter journey times.

Those against it, who have often been the most vocal in the debate, argue it’s an unnecessarily costly alternative (the latest budget estimate is £42bn) to upgrading our existing rail network that will damage the countryside and destroy people’s homes (and property values) without delivering the benefits promised.

We put your engineering questions about the scheme to HS2 Ltd’s head of engineering and operations, Tim Smart, as well as independent experts Philippa Oldham, head of transport at the Institution of Mechanical Engineers (IMechE), and Prof Felix Schmid from Birmingham University’s Centre for Railway Research and Education.

Why can’t we upgrade the existing West Coast Main Line (WCML) and/or the Chiltern Main Line to provide the necessary capacity andmake room for faster trains?


Tim Smart, HS2 Ltd

Tim Smart: The WCML has already been upgraded, first by British Rail during the 1960s and again by Network Rail between 2004 and 2008 at a cost of over £8bn. Further upgrades are simply not economically viable and they do not offer the step-change in capacity needed for continued economic growth. To take advantage of improvements in more efficient passenger rolling stock which can carry higher passenger numbers, yet are lighter, faster and more efficient in energy terms, there are limitations imposed by the existing WCML alignment.

The higher capacity of the proposed HS2 line in terms of frequency, speed and type of train means significantly more passengers can be moved per hour providing greater capacity more efficiently. Furthermore HS2 extends the benefits of better connectivity and capacity to important northern cities not currently served by the WCML and releases capacity on it for the benefit of other communities and businesses along the route.

The reasoning is similar for the Chiltern Main Line and it too has also been upgraded in recent years. However a further complication with this line is that it serves a significant number of smaller communities and along various sections of its route is more akin to a commuter type railway than an inter- city one. Consequently the issue of compromise on the stopping pattern for those communities it currently serves becomes more acute.

‘upgrading a running railway is fraught with significant performance and financial risks that were not experienced with HS1’

Philippa Oldham: HS2 aims to move the InterCity services to separate lines, freeing up capacity on the WCML for local, freight and commuter services. Having a mix of low-speed and high-speed trains on the same line is not really an option as this restricts the capacity of the line. Capacity is affected by a large amount of variables that include infrastructure factors (eg signalling systems and track structure), traffic parameters (eg train mix and timetables) and operational factors (eg maintenance restrictions and station dwell times). Variable speeds on the same railway severely restrict capacity. It will not be possible to remove the existing traffic from the WCML to avoid this phenomenon. Recent experience shows that the upgrading of a running railway is fraught with significant performance and financial risks that were not experienced with HS1.

Felix Schmid: Adding two further tracks to the WCML would be very difficult, very expensive and very disruptive. The WCML was built in the Victorian period, with the technologies available at the time. Reconstruction of the railway would take 10 years or more and would have a huge impact on the environment and the communities. Enhancing the Chiltern Main Line would be more straightforward but traffic is increasing rapidly on this former secondary route and any upgrade would also be very disruptive.


Source: HS2 Ltd

HS2 opponents say there is no need to replace the West Coast Main Line.

Why separate HS2 from HS1, rather than linking the two by using tunnels to have the lines meet around St Pancras or Stratford, especially as those areas are closer to London’s main business centres than Euston?

TS: We recently held a consultation on several proposed phase one route design refinements – including proposals on how we could link HS1 and HS2. The consultation closed on 11 July. The responses to the consultation will inform the transport secretary’s decisions on the design for the phase one route. The government aims to reach a final decision on the design that will be incorporated into the hybrid bill in the autumn to allow it to be deposited in Parliament by the end of the year with the formal Environmental Statement.


Philippa Oldham, IMechE

PO: The Institution believes that there would be enormous potential for the rest of the UK in providing a link around London, which would link the Midlands and North of England, Wales and Scotland to the Channel Tunnel. Journey times from these UK regions to mainland Europe would be considerably shorter and more convenient, thus encouraging even greater modal shift from short-haul air to high-speed rail with attendant emissions savings. Indications are that recent designs are moving in this direction.

To what degree are the HS2 plans based on proven technology? How close are we to developing the necessary new technology and what work still needs to be done?

TS: The design and development of the scheme does not rely on technologies that have yet to be invented. The technologies already exist and there may be further development from which HS2 will benefit. Not all the technologies have been used together, so one of our big challenges will be their integration to achieve high levels of performance.

PO: There needs to be an aspect of innovation within this project to make sure that we design a system that is sustainable and fit for future requirements. 400km/h has still not been done elsewhere, but the HS product is moving in that direction, there are still some challenges that remain (eg noise, aerodynamics, energy efficiency). Maximising capacity of the built infrastructure at high speeds is a challenge for the train control system, and the performance and reliability of the train braking system, including adhesion at the wheel/rail interface.

FS: The current plans for HS2 involve tried and tested technology for the infrastructure – that is, tracks, bridges and tunnels. It is likely that the trains will be built with more advanced technology than that common today, eg permanent magnet machines, active suspensions and pantographs. The railway control system (signalling) will be an updated form of the European Rail Traffic Management System, possibly involving ETCS Level 3, ie the moving block version of the European Train Control System. However, most of the “novel” systems are currently being tested extensively on other railway networks and will be introduced only if they are appropriate.


How much more energy and power do 250mph (400km/h) high-speed trains need compared to conventional ones?

TS: Our preliminary calculations, which are dependent on what assumptions are made about service patterns, timetables and type of trains, indicate an annual electricity consumption figure of around 600 GWH ¬– less than 0.2% of today’s total UK consumption in phase one. For phase two we estimate that it will be 2TW – less than 0.6% of today’s total UK consumption. The peak power demand values when operating at conventional speed have not been calculated.

FS: This depends to a limited extent on the quality of the aerodynamic design but, in simple terms, the energy requirement increases with the square of the speed while the power drawn by the train goes up with the cube of the speed. On the assumption that the cross-sectional area and the length of the trains is similar to that of the comparator train, doubling the trains’ speed from 200km/h to 400km/h will increase energy use by 300% and the pantograph(s) will have to collect 700% more power. Current collection is a major limiting factor of high-speed railways due to the nature of the electrical contact interface, the noise generated by the pantograph and the difficulty of maintaining good performance in high winds and when ice forms on the overhead line.


Source: HS2 Ltd

The HS2 plans include a new East Midlands hub station between Nottingham and Derby.

One reader argues that running trains at 186mph (300km/h) as on HS1, rather than the proposed 250mph (400km/h), would be easier, require less land and save energy. Do you agree and, if so, what are the advantages of running trains at the higher speed?

TS: HS2 is primarily about providing capacity and also of course connectivity. By running trains at higher speeds more passengers can be moved per hour more sustainably than other modes of transport. Reasonable allowances must be made for the future capacity and this of course must include speed as a factor. If we did not design for the higher speeds that are available with modern technology and designed for routinely on other high speed railways throughout the world, this capacity would be denied our future generations and we would be faced with upgrades and associated disruption that has occurred on the UK’s railways in the past as it struggles to keep up with demand. 

‘If we did not design for higher speeds, capacity would be denied our future generations and we would be faced with upgrades and associated disruption’ 

Whilst the design of HS2 for operation at 300km/h (186mph) would require slightly less land and use less energy, it wouldn’t necessarily be easier. The civil engineering assets on HS2 will be designed for a 120 year life. To ensure that future advances in rolling stock technology can be utilised fully, the track alignment is designed, where possible, for speeds up to 400km/h (250mph). However, the maximum speed of trains running on HS2 in the early years of operation will be 360km/h (225mph), with the majority of trains timetabled to run at 330km/h (206mph). This provides an operational margin which allows trains to operate at a higher speed should it be required to recover from minor delays and keep to the timetable.

PO: The lower carbon credentials of moving people and freight by railway is also an important factor as we move towards our legally binding climate change act targets in 2020 and beyond. At the Institution we believe the average speed for HS2 should be kept to 240kph (with a maximum of 320kph) until a truly decarbonised electricity supply mix is available. It is important to get the optimal speed to minimise the energy demands. Speed could then be increased at a rate that reflects the reduction in carbon emission of the electricity supply, thus ensuring no overall increase in CO2 emissions. The land take is unaffected by higher speeds, although the vertical and lateral alignment may change for reasons of passenger comfort.


Felix Schmid, Birmingham University

FS: Designing a railway for 300km/h rather than 400km/h reduces the tunnel cross-sectional area, the curve-radii, the rating of the electrical supply and, to a limited extent, the complexity of the signalling system. The energy requirement is reduced by 45%, while the power supply can be rated 58% lower. The land take also reduces. However, HS2’s plan is to build the railway for 400km/h, thus future proofing it, but to operate it at about 330km/h.


What impact do acoustic waves from 250mph trains have on the rails, people and surrounding wildlife? One expert in particular has raised the danger of Rayleigh waves in the track causing problems and even derailments. What research has been done to investigate and mitigate these issues?

TS: The cause of high levels of vibration from Rayleigh waves may be compared to the bow wave from a ship. This phenomenon is well understood and is managed by design and construction techniques. Current high speed railways recognise the situations where this could occur and incorporate measures such as soil strengthening or bridging over soft ground to ensure Rayleigh waves do not adversely affect train operations or damage the infrastructure. These measures also ensure that there is no impact on people and surrounding wildlife. There is currently research being carried out by leading universities in the UK to develop more effective and less conservative solutions.

PO: The main acoustic problem from high speeds is the pressure wave impact on passengers (their ears) in tunnels. This can be designed out through good tunnel ventilation and portal design, and sealing the trains. Noise mitigation is a well-developed science and generally, as HS1 has proven, high-speed rail noise is seen as less intrusive by the neighbours than motorway noise.


Source: HS2 Ltd

HS2 Ltd says the line would be built to accommodate future faster trains.

Why should we favour a project that will take so long to complete that by the time it opens it may no longer suit our transport needs?

TS: We simply must find sustainable solutions that allow the nation’s infrastructure to support this growth in business, industry, population and travel. High speed rail provides an effective solution to overcoming this, but must be in harmony with other methods of transport, above all in maximising connectivity. Predicting the UK’s future needs is based on the best possible assimilation of information on how to meet this challenge, looking across the broad spectrum of issues including energy use, transport methods, available technology, competing demands and experience elsewhere.

FS: This is an argument that can be put forward against ANY infrastructure project. It is entirely fallacious in the HS2 context because the railway will change the economic geography of Britain and create its own demand, in the same way the motorways changed Britain in the 1960s and 1970s.


Source: HS2 Ltd

HS2 would include a new Manchester terminal next to the existing Piccadilly station.

How many engineering jobs will HS2 create in the UK, and what are these figures based on?

TS: I can’t provide a specific engineering jobs figure at this stage of the project but according to an Albion Economics report produced for Greengauge 21 (June 2013) HS2 job numbers (direct and supply chain) are predicted to be more than 22,000 in the next five years. In addition, they predict around 50,000 concurrent jobs will be generated by HS2 towards the second half of the next decade. The opportunities for British engineers and associated professions from HS2 are tremendously exciting.

Readers' comments (22)

  • Rather biased panel with little regard to the limitations of HS2 one track each way with dedicated tunnel per track. HS2 fails to add the capactities required as a separate one track each way unreliable/unavailable approach. Obsession with phase 1 route 3 and failure to consider the WCML, MML, ECML as a joint three route capacity issue.

    Lack of thoroughness is a hallmark of HS2 to-date and also partial treatment of the needs.

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  • Besides the representative of HS2 itself - an obvious place to start with questions about the scheme - the panel was chosen to include people with expertise in the field of railway/transport engineering but who were independent from the project. The interest groups we examined that outrightly opposed the plans came from a political standpoint not an engineering one, and we felt it would be inappropriate to include them in this this kind of article. In this sense, we believe that the majority of the panel was not biased but rather happened to hold views generally supportive of HS2.

    However, we would be interested in hearing from any Engineer readers with appropriate expertise in the field who wish to argue for an alternative proposal for addressing Britain's rail capacity issues, especially as, so far, most of the prominent opposition to the scheme has come from politicians, journalists, PR people, celebrities and residents of the Chilterns, who have little or no knowledge of the engineering and planning challenges involved in solving such a difficult and large problem.

  • Chris Stokes, Rob Holden, Jonathan Tyler, are just 3 who spring to mind who could offer the balancing view.

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  • Opposition comes from a far wider range of people than that including, economists, rail experts, employers organisations and local authorities from across the UK. The article makes no mention of the severely flawed business case which has been heavily criticised by the NAO and PAC and which you allow Tim Smart with his vested interest in the project to dismiss with an airy wave. I understand why your title would focus on the engineering issues, and that's fair enough, but decisons about HS2 have to take into account a far wider range of issues, not least the costs and benefits of the project which are extremely problematic to say the least.

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  • Decisions about HS2 do have to take into account a wide range of issues and the decision will ultimately be a political one. As you say, economists, employers' organisations and local politicians are all weighing in. That's why we, as an engineering magazine, felt it was important to give a voice to engineers. The engineers we contacted happened to support the scheme. As said above, we would be very interested to hear from engineers with relevant expertise who have differing opinions.

  • Ed - your havin a larf, surely?

    HS2 is not an engineering problem per se - I quote
    "TS: The design and development of the scheme does not rely on technologies that have yet to be invented. The technologies already exist"

    Anyone with the "necessary experience" surely has a vested interest in building more of the thing they are "experts" in?

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  • They plan to increase motorway capacity by automatically running cars a few metres apart. Surely it would be easier with rails to fun trains much closer. This would easily give the capacity increase needed. Some new infrastructure would be needed at stations, but could otherwise use existing lines, would be a good engineering challenge and we could sell it to the world.

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  • Since it's perfectly clear that the whole thing is based on relatively well known technology we are only left with the economic questions anyhow.

    Big projects tend to go wrong because they make big assumptions and we're not very good at that. It's not fallacious to decide that 40 or more billion pounds is a big gamble to make based on our history of getting things right.

    I think we haven't had explained to us at all why people travel, what kinds of people do, what they would do instead if there was no train etc. It simply feels as if this is going to be another giant and expensive blunder and "railroading" it through with dismissive comments is just avoiding the question which has never, in my experience, been associated with a successful project.

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  • A good set of comments on the engineering perspective of HS2, and the increase in capacity it will bring.

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  • The technology is all well tried and tested many times over so for the life of me I can't understand how it can possibly take so long and be so expensive to build a HS network in the UK compared with most other countries that have done it. The channel tunnel was built quite quickly by starting at both ends and meeting in the middle. Why the heck can't the networks be started in Glasgow/Edinburgh/Cardiff/Bristol as well as in London at the same time with a view to meeting in the middle?

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  • Notwithstanding the technology and engineering and associated
    financial, political and ecological costs, I have yet to hear a succinct, coherent and convincing argument as to WHY we apparently "need" HS2. Any suggestions?

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  • The Channel Tunnel is not a good example to mention.
    It was way over budget (about double) and way over the programme. (again double).
    And it has and still is a financial liability. It will never recoup the cost involved.
    If these things are not important, then build HS2.

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