On 24 June 2019, the House of Commons unanimously passed an amendment to the Climate Change Act that committed the UK to net-zero carbon emissions by 2050. Previously, the target had been 80 per cent of UK’s 1990 emissions. This followed the report by the Committee for Climate Change (CCC) (issue 177, Aug/Sept 2019), which showed that net-zero carbon by 2050 was an achievable, though highly demanding, target.
The CCC report was published shortly before the rail industry decarbonisation taskforce finalised its report in July 2019. This was initiated in February 2018 following Rail Minister Jo Johnston’s call for the rail industry to remove all diesel-only trains by 2040, leaving only diesel bi-mode trains. The final taskforce report concluded that diesel bi-mode trains could not be part of a permanent solution if the requirement is now to be net-zero. Yet the report noted that, until 2050, bi-mode trains will have a useful transitional role.
The decarbonisation report concluded that achieving net zero would require a mix of electrification, hydrogen and battery trains. It considered that achieving net zero may require 4,250 route kilometres of electrification and noted that “electric traction, where the line is sufficiently intensively used, provides the lowest whole-life carbon impact, and delivers services that are faster, more reliable, quieter and less polluting than diesel traction”. However, on less intensively used lines, the report concluded that electrification may not justify the investment cost.
The report contained no map or list of routes that made up these 4,250 kilometres of electrification. It seems that the first such map will not be available until July 2020, when Network Rail’s traction decarbonisation network strategy group is due to produce its interim report prior to its final report in October. This will inform the Government’s decisions on electrification, battery and hydrogen traction.
Defining ‘intensively used’
The amount of electrification required depends on the grey area between routes that are obviously intensively used and those with little traffic. To assess how much electrification is required, Rail Engineer considered the services in each table with unelectrified lines in the national rail timetable (NRT) to produce a spreadsheet. This contained the unelectrified route mileage, the stations between which electrification was required, hourly frequency, estimated number of coaches per train, whether there was a direct service to London, whether lines used by freight route and, finally, the type of service.
Service types were classified as either: branch line, commuter, cross country (long routes linking towns and small cities with one or two large cities), inter-city core routes (routes connecting London to large cities, NE/SW cross country services and transpennine), inter-city extensions (branches from core routes to locations that currently have a through service to London, also Scottish inter-city services), urban (in populated area with no major commuter flow) and rural.
In 2016-17, the total CO2 emissions from the diesel passenger train fleet and from freight locomotives were respectively 1.36 million tonnes and 0.55 million tonnes. Achieving net zero by 2050 requires the elimination of all diesel traction and, in some cases, carbon offsets.
The only zero-carbon traction options are electrification, hydrogen (produced by electrolysis) or batteries, provided that the electricity generation is carbon-free. This has already been achieved, as Network Rail procures all its rail-traction electricity from zero-carbon nuclear generation.
The power of electric trains is limited only by the current that can be drawn through their pantographs. For this reason, electric trains are the only form of transport that can move heavy freight or passengers at high speed with zero-carbon emissions. The decarbonisation report considers that electrification is the only alternative to diesel-hauled freight, which accounts for 29 per cent of rail traction emissions.
A National Infrastructure Commission report noted that only 13 per cent of freight is hauled by electric locomotives. This report concluded that electrifying 515 kilometres of key freight routes would enable nearly two-thirds of freight services to be electrically hauled. As it is not feasible to electrify all freight routes, there will always be some diesel-hauled freight and engineering trains. Emissions from such trains would require carbon-offset measures, such as tree planting, if rail traction is to achieve net-zero carbon emissions.
An important consideration is that electric trains offer the high speed and high acceleration needed to encourage a shift to rail from less carbon-friendly transport modes. It is likely that the carbon savings from such a modal shift would be of a similar magnitude to rail’s current carbon emissions.
The decarbonisation report considers that hydrogen trains are only suitable for shorter-distance self-powered trains with a maximum speed of 75mph. It also concludes that battery trains are only suitable for “short hops off wire”. However, this categorisation takes no account of the need for high acceleration, which is essential for commuter services.
Hydrogen trains are certainly a viable option for rural routes and may be developed to the stage where they are suitable for cross country and semi-intensive urban services. However, their capability will always be limited by energy storage constraints as, to store the same amount of energy, hydrogen tanks need to be seven times the volume of diesel tanks. This could reduce passenger capacity if hydrogen has to be stored within the train. For this reason, electric/hydrogen bi-modes are probably not a feasible option.
Battery-powered trains could operate shuttle services on short branch lines, where they could be charged during the layover period. However, the time required for charging may require extra trains to maintain the timetable. Batteries could be used for “short hops off wire” in battery/electric bi-mode trains, for which a 60-mile round trip was considered to be the maximum possible. Such hybrids could also be used on routes with significant electrification challenges, such as the Welsh Valley services, for which discontinuous electrification may be appropriate as the only trains are a dedicated fleet.
The decarbonisation report proposed that battery trains could facilitate discontinuous electrification. However, there are many reasons why there seems to be no discontinuous electrification on mainline railways outside the UK. These include the cost of transmitting power across the break in the contact wire and arrangements to ensure pantographs are lowered. Moreover, recent initiatives, such as surge arresters, can eliminate bridge reconstructions and reduce the need to consider discontinuous electrification.
The logistics and economics of operating a small proportion of battery or hydrogen trains in an otherwise largely electric train fleet also needs to be considered. In the long-term, unelectrified branch lines within electrified areas are unlikely to be the optimum solution, as such lines could be electrified at low cost as part of a rolling programme, especially if these are low-speed lines. As hydrogen trains require specialist facilities, a small fleet of hydrogen trains may not be justifiable in areas of significant electrification.
Battery trains are a potentially useful decarbonisation transition technology. However, their long-term viability depends on battery costs, which could become unacceptable as demand for batteries increases with worldwide decarbonisation initiatives.
Electrification mileage required
Considering the above, each non-electrified line in the NRT was assessed to determine its priority for electrification as shown below:
- Definite – high-priority intensively used services comprising core inter-city services, commuter services and freight routes, inter-city extensions that provide through services to London (except for short hops for which battery/electric bi-modes might be feasible), cross-country services through populated areas, other freight routes, urban services in densely populated areas;
- Possible further electrification – remote cross-country services, inter-city extensions with infrequent service not suitable for battery power, other urban services, hourly rural services in reasonably populated areas;
- Unlikely but possible – high-mileage inter-city extension with alternative route, little-used rural routes that feed into main lines or are close to population centres;
- Never – remote rural routes through sparsely populated areas which could be operated by hydrogen trains;
- Battery trains – suitable for operation by trains that are either hybrid battery-electric trains which charge their batteries whilst operating on the electrified network or have batteries charged at either end of the line during their layover.
The resultant estimate of electrification required by category and route type is shown in the map and table 1. It is noteworthy that the 4,327 route kilometres of definitely required electrification is almost identical to the 4,250 kilometres figure in the decarbonisation report.
The definite electrification requirement was that which eliminates diesel traction whilst maintaining train performance. It is not possible to state how much electrification will eventually be required, due to many current unknowns. These include the future cost of electrification, the eventual capabilities and costs of battery and hydrogen traction and the extent to which Treasury investment-appraisal rules value carbon savings. For this reason, the analysis considered further possible and unlikely electrification scenarios.
It concluded that the route kilometres of electrification required under ‘definite’, ‘possible’ and ‘unlikely’ scenarios would be respectively 4,327 km, 5.993 km and 7,029 km. It concluded that electrification could never be justified for 1,401 route kilometres of the network. Increasing the electrified network by 4,327 route kilometres by 2050 under the ‘definite’ scenario would require a rolling programme of around 144 route kilometres a year, which is about 50 per cent more than the delivery rate of the previous ten years.
The traffic metric
It is important to assess the relative contribution of electrification, hydrogen and batteries which, for passenger services, is broadly proportional to the traffic carried. This was estimated from an assumed number of coaches on each service, the service frequency shown in the timetable and considering the service operates 17 hours a day, 363 days a year, to estimate the annual vehicle mileage for each type of traffic as shown in table 2.
This relates to traffic on currently unelectrified lines which is broadly 27 per cent of all traffic, given that 73 per cent of the passenger fleet are electric trains. Thus, for example, rural lines that will never be electrified carry about one per cent of passenger traffic although they constitute nine per cent of the total route mileage.
As previously mentioned, there are many unknowns about future long-term decarbonisation options. For this reason, a range of the percentage passenger emission reduction of each type of traction was derived using the difference between the definite and possible electrification scenarios. Freight electric haulage in the definite and possible scenarios was assumed to be respectively 70 and 80 per cent.
The figures in table 2 derived by this analysis show that, if a net-zero-carbon railway is to be achieved without a reduction in train performance, a substantial electrification programme will account for almost all the emission reductions. Nevertheless, there is a significant role for hydrogen trains whilst battery traction will have a minimal role.
Regardless of the decarbonisation imperative, electrification schemes can only be authorised if they have a robust business case. Reports such as Network Rail’s 2009 electrification route utilisation strategy and RSSB’s 2007 study on further electrification of Britain’s railway network (T633) provided the basis for the business cases that justified the Midland and Great Western main line electrification schemes. However, these schemes were later fully, or partly, cancelled due to rising electrification costs which, on Great Western, had risen to £2.3 million per single track kilometre (stk).
The reasons for this increased cost are detailed in the Railway Industry Association’s electrification cost challenge report, which explains why the Great Western scheme was an aberration and concludes that electrification should cost between the £1 and £1.5 million per stk, as has now been achieved by recent projects. Assuming there are, on average, 2.5 stk per route kilometre, the electrification of 4,327 route kilometres (10,892.5 stk) in the ‘definite’ scenario would cost around £14 billion, or £500 million per year over 30 years. If delivered by a dedicated expert team as part of a rolling programme, it is likely costs would be further reduced, for example by initiatives to reduce the number of bridge reconstructions.
It is to be hoped that the unit electrification costs in the RIA report could provide the basis for business cases for busy non-electrified routes, including schemes that were recently cancelled or cut back. However, this depends on government having confidence that the industry can reliably deliver electrification in a cost-effective manner.
In Scotland, the Scottish Government is committed to a substantial rolling programme of electrification, for which the long-term aspiration is as shown on the map.
For England and Wales, the process for enhancements, including electrification, is the UK Government’s rail network enhancements pipeline, which contains just two electrification schemes totalling 24 route kilometres of electrification (Bolton to Wigan and Huddersfield to Dewsbury).
One reason for the lack of electrification schemes is that this pipeline process document does not mention decarbonisation. This omission highlights an issue that Government must address if it is to meet its net-zero target – that the requirement for carbon reduction should be addressed in all policy documents, ensuring that investment appraisal adequately values carbon savings.
The 2007 RSSB electrification study (T633) monetarised carbon savings for exemplar electrification schemes using a value of £79 per tonne saved from the Department for Transport (DfT)’s WebTag process. The resultant carbon savings were 20 per cent of the monetary benefits.
Under current appraisal rules, there will never be a zero-carbon railway, as it is not possible to develop business cases for all the required electrification schemes.
An urgent requirement
A common theme of the CCC net-zero report is that delivery must progress with great urgency if this target is to be achieved by 2050 and that government must act accordingly.
It is also clear from this report that rail decarbonisation is quite straightforward, compared with the technologies and behavioural changes required in other sectors. However, the reality is that, other than in Scotland, it seems that any significant plans for electrification must await the outcome of the traction decarbonisation network strategy. It is understandable that the development of this strategy will take some time, especially as transitional arrangements, which are not part of this analysis, need to be considered.
However, there are heavily used routes which are an obvious and urgent electrification requirement that should not require further analysis. A start on such routes should be made now as experienced electrification teams are about to be disbanded after the completion of 800 route kilometres of electrification in ten years. The loss of these teams can only increase the cost of future schemes.
Another factor that needs to be considered is air quality. As increasing numbers of cities introduce zero-emission zones, diesel emissions at stations within such zones are likely to become increasingly unacceptable, unless it can be shown that there is a plan to eliminate them.
It would seem certain that climate change will continue to rise up the political agenda, putting increased pressure on government departments to act. For rail, the challenge would seem to be persuading government that novel self-powered traction can only ever be a small part of the solution, as this cannot ever have the same power and range of the high-powered diesel trains that need to be replaced. Hence, a substantial electrification programme is required to achieve a net-zero-carbon railway.
It must be understood that the only alternatives to a large-scale electrification rolling programme are slower trains, as novel self-powered traction replaces all diesel trains, or retaining diesel traction and abandoning any significant further rail decarbonisation.
Rail Engineer will be glad to share the spreadsheet on which this feature is based with any industry partner that might find it useful.