End of the line? Phasing out diesel-only trains

Last week, the Government announced its the ambition to remove diesel-only trains from the tracks by 2040. With public concern about air pollution and transport’s contribution to climate change continuing to rise, we consider the different options for phasing out diesel trains and some of the benefits.

Cleaning the tracks

Diesel trains contribute to both air pollution and climate change, with 29% of trains in service on the UK’s rail network currently running on diesel. Overall, the transport sector has largely failed to reduce its greenhouse gas emissions as part of efforts to tackle climate change. In rail specifically, greenhouse gas emissions have risen by 30% since 1990 in absolute terms. Similarly, significant levels of harmful air pollution have been recorded both on-board, and in the vicinity of, diesel-only trains. In fact, when in 2015 London Paddington station was in breach of healthy pollution limits, the air quality inside the station was found to be significantly worse than outside.

In this context, the Rail Minister Jo Johnson MP’s speech this week challenged the rail industry to publish a long-term strategy - aimed at facilitating substantial pollution and emission reduction - by the autumn of 2018. Government policy has for a long time aimed at the full electrification of the rail network, whereby conventional engine-based propulsion is replaced by electric – both overhead and third-rail – traction systems. However, such plans have had a troublesome journey.

Electric dreams

In 2009 the then Labour Government announced the first large-scale electrification plans, including schemes on both the North West and the Great Western main line. The Coalition Government continued these proposals, modifying them to include the Midland main line and other schemes.

However, in June 2015 the Secretary of State for Transport paused the Trans-Pennine and Midland main line electrification schemes. Both were subsequently resumed in September 2015 with delayed completion dates. It was argued that the focus should be on delivering the Great Western upgrade on time and on budget.

In November 2016, delays to works on four areas of the Great Western line were announced. Subsequently, in July 2017, some electrification works were cancelled altogether between Cardiff and Swansea, between Kettering, Nottingham and Sheffield, and between Windermere and Oxenholme. It was argued that greater capacity and environmental benefits could be achieved without the substantial cost and disruption associated with full electrification works by deploying new bi-modal trains. Bi-modal trains are hybrids capable of running on both electricity where overhead cables are available and diesel where they are not.

A change of track?

Although approximately 34% of Britain’s rail network was electrified in 2015-16, experts are sceptical about the potential for full electrification. Electrification coverage has increased over 2017 and into 2018, yet has clearly suffered major set-backs, primarily due to rising costs.

The Rail Minister’s speech last week reaffirmed this change in policy direction away from complete electrification, promoting the use of bi-modal models and the potential of hydrogen-fuelled trains. Train manufacturer Alstom has recently tested hydrogen trains in Germany, whose only waste product is steam. The attention on this new train technology supports the growing interest in hydrogen as a low-carbon fuel. Existing research suggests that by repurposing the gas network to use hydrogen the UK is well-placed to become a global leader in this area, with the Government announcing new investment in hydrogen infrastructure.

As highlighted in the recent industrial strategy white paper, the Government also supports the long-term goal of developing the battery storage industry in the UK, given its importance to the future energy system. Battery-powered, electric-traction ‘hybrid’ trains could support this economic ambition, with the Northern franchise expected to deliver such trains on the Windermere branch from 2021.

Counting the cost

Underpinning debates about these delays have been conflicting claims about the costs and benefits of electrification. The National Audit Office (NAO) has been highly critical of several aspects of electrification, particularly the optimistic cost and productivity savings. For example, the initial £1.7 billion cost of electrifying the London to Cardiff line was revised up to £2.8 billion in the Hendy review. Initial estimates of the economic benefits - such as £100 million a year for the South West region through reduced journey times and added seating – have subsequently been viewed sceptically.

By contrast, delays to track upgrades also carry costs. Both the NAO and House of Commons’ Transport Select Committee have pointed to the additional costs for rail companies - and subsequently the customer – from investment uncertainty, continuing to run inefficient diesel trains, and the necessity of switching to interim, bi-modal, solutions.  

Alongside cost, the benefits of reducing diesel usage to public health and the environment are substantial. Fully electric trains produce virtually no toxic air pollution at the point of use and provide a 20-60% reduction in total associated CO2 emissions relative to old diesel-only models, a figure falling constantly as electricity decarbonises.

By contrast, bi-modal train models are estimated to lower particulate matter pollution by 90% and nitrogen dioxide emissions by 50-59%.  Relative to old diesel-only trains, new bi-modal models would reduce total associated CO2 by approximately 12-30% by cutting diesel usage by 40-50% and improving engine efficiency.


With air pollution and climate change both significant issues of concern to the public, this week’s ministerial announcement, even if less ambitious than the previous policy of full electrification, should be welcomed.

Philip Box is a researcher at Bright Blue