Meghan Hodges
Trains are a major source of pollution, with diesel trains being the most polluting. Research has found that on-train concentrations of nitrogen dioxide can be up to 13 times higher than those next to major central London roads, with pollution increasing significantly when trains are in tunnels or idling at stations. While electric trains are a more environmentally friendly alternative, the UK's train system has been slow to modernise and decarbonise, with a continued reliance on diesel trains. However, rail is still considered one of the greenest forms of transport for passengers, with a lower carbon footprint intensity compared to other modes of transport.
| Characteristics | Values |
|---|---|
| Pollution in tunnels or stations | Pollution increases when trains are in tunnels or idling in stations. |
| Diesel locomotive fumes | Passengers sitting in the rear carriages of diesel trains are more exposed to fumes, possibly due to exhaust intake through windows or AC. |
| Nitrogen dioxide levels | On-train concentrations of nitrogen dioxide can be 1-13 times higher than near major central London roads. |
| Carbon emissions | Electric trains produce 24% of the emissions of diesel trains. |
| Energy efficiency | Electric trains are three times more energy-efficient than diesel trains. |
| UK government plans | The UK government has pledged to remove all diesel-only trains from the network by 2040 and achieve a net-zero railway network by 2050. |
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What You'll Learn
Electric trains produce 24% of diesel train emissions
Trains are one of the greenest forms of transport, but they still contribute to pollution. Pollution increases when trains are in tunnels or idling in stations. Diesel trains are particularly polluting, and passengers on these trains are exposed to fumes, particularly when sitting in the rear carriages.
In the UK, the government is investing in electrifying more of the railway to reduce the number of diesel trains. This is because electric trains produce 20-35% less carbon per passenger mile than diesel trains. For example, an electric Intercity 225 train emits about 45g of CO2 per passenger per kilometre, while some diesel locomotives emit more than 90g of CO2 per passenger per kilometre.
In the US, nearly all locomotives are propelled by diesel-electric drives, which emit 35 million tonnes of CO2 and produce air pollution that causes about 1,000 premature deaths annually. Popovich et al. found that battery-electric trains have the potential for both economic benefits and emissions reduction. A transition to battery-electric rail is supported by plummeting battery prices, increasing battery energy densities, and access to cheap renewable electricity.
Hybrid trains, which use a combination of battery power and diesel engines, are also being introduced. These trains reduce the carbon emissions of diesel trains by 19%.
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Diesel trains' carbon emissions are twice electric trains'
Rail is one of the greenest forms of transport, but trains do create pollution. Pollution levels increase when trains are in tunnels or stationary at stations. Diesel trains have been found to expose passengers to higher levels of fumes, especially in the rear carriages.
Diesel trains' carbon emissions can be twice those of electric trains. Figures from the UK Rail Safety and Standards Board show some diesel locomotives emit more than 90g of CO2 per passenger per kilometre, compared with about 45g for an electric Intercity 225. The source of the electricity used to power electric trains can make a big difference, too. For example, France generates about 75% of its electricity from nuclear power, while Poland generates about 80% of its electricity from coal.
In the UK, the National Grid is decarbonising, which means removing fossil fuel power stations in favour of low and zero-carbon alternatives. This will help to reduce the carbon intensity of electricity used by trains.
Hybrid trains, which use a combination of battery power and diesel engines, can also help to reduce carbon emissions. According to the Institute of Electrical and Electronics Engineers, hybrid trains reduce the carbon emissions of diesel trains by 19%.
The development of more efficient and cheaper battery technology has the potential to further reduce emissions from trains, as well as other forms of transport.
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Nitrogen dioxide levels in trains vs London roads
While trains are one of the greenest forms of transport, they still contribute to pollution. Nitrogen dioxide (NO2) levels on some trains in the UK have been found to be 13 times higher than on one of London's busiest roads, Marylebone Road. This is due to the design of the trains, which combines diesel and electric power. When these trains switch from electric to diesel, NO2 pollution spikes.
The Rail Safety and Standards Board (RSSB) conducted a study on the Hitachi-built trains, which found that NO2 levels peaked at more than 13 times the average recorded on Marylebone Road. This has raised concerns about the air quality on trains and in stations, with the UK government launching a review and considering raising standards.
The RSSB also examined six types of diesel trains and found high levels of particulate pollution on older diesel trains operated by Avanti West Coast, including the Super Voyager class 221 models built by Alstom. Passengers on trains pulled by diesel locomotives are more exposed to fumes when sitting in the rear carriages, possibly due to how the exhaust is drawn into the train's windows or air conditioning system.
While the quality of air on train services remains within legal workplace limits, the issue of high NO2 levels is being addressed. Cross-industry research is underway to understand and address the problem, and the government is working to electrify more of the railway network to reduce the number of diesel-operated trains.
In terms of nitrogen dioxide levels, trains with diesel-electric power sources can have significantly higher NO2 levels compared to busy London roads like Marylebone Road. However, it is important to note that the UK's overall NO2 concentrations at the roadside have been decreasing annually since 2021, reaching their lowest point in 2023.
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Rail is one of the greenest transport methods
Electric trains produce 24% of the emissions of diesel trains and are around three times more energy-efficient. Electric trains are also better for passengers' health and are faster, more reliable, offer greater capacity and smoother journeys. Electrified lines also have air quality and noise benefits in and around stations.
The UK government has committed to providing a "net-zero railway network by 2050", with the ambition to remove all diesel-only trains from the network by 2040. Rail minister Chris Heaton-Harris said: "The safety of staff and passengers is our absolute priority."
While rail is one of the greenest forms of transport, there are still issues with pollution. Pollution increases significantly when trains are in tunnels or idling in stations. Passengers on trains pulled by diesel locomotives are more exposed to fumes when sitting in rear carriages, possibly due to how the exhaust is drawn into the train's windows or air conditioning system.
However, overall, rail is a low-carbon mode of transport, and the continued electrification of rail lines will further improve its environmental credentials.
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UK's train system is stuck in the dark ages
The UK's train system has evolved significantly since the construction of the first local isolated wooden wagonways in the 1560s. However, despite this long history, some argue that the UK's train system is stuck in the dark ages due to a range of issues, including pollution, privatisation, and safety concerns.
One of the main concerns regarding the UK's train system is pollution. While rail is considered one of the greenest forms of transport, with the carbon footprint intensity of trains continuing to decrease, there are still issues with diesel trains polluting the air. Pollution increases significantly when trains are in tunnels or idling at stations, and older diesel trains have been found to have high levels of particulate pollution. The Rail Delivery Group has called for government investment to electrify more of the railway and eliminate diesel trains, which produce more carbon emissions than electric trains.
The privatisation of the UK's train system in the 1990s is another issue that has plagued the network. While passenger volumes have increased since privatisation, government subsidies to the rail industry have also tripled, and train fares have increased. The Hatfield accident in 2000, caused by a rail fragmenting due to microscopic cracks, also damaged the public image of rail travel and led to the collapse of Railtrack, the company responsible for track and infrastructure.
Safety concerns have also been raised about the UK's train system. While railways have become significantly safer since privatisation, there have been several prominent accidents, including the Southall and Ladbroke Grove rail crashes, caused by trains passing stop signals. These incidents have highlighted the need for improved safety measures and infrastructure upgrades.
Overall, while the UK's train system has a long history and has undergone many changes, it continues to face challenges related to pollution, privatisation, and safety. Addressing these issues is crucial to ensuring that the network can provide a safe, efficient, and environmentally friendly service.
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Frequently asked questions
Trains do create pollution, but rail is one of the greenest forms of transport on a passenger level. Electric trains produce 24% of the emissions of a diesel train and are three times more energy efficient.
Diesel trains are the most polluting, with some diesel locomotives emitting more than 90g of CO2 per passenger per kilometre.
In 2021, the UK government set out a plan to decarbonise all domestic transport by 2050, including the removal of all diesel-only trains from the network by 2040.
Taking the train is often more environmentally friendly than travelling by plane, car or ferry. For example, a journey from London to Madrid would emit 43kg of CO2 per passenger by train, but 118kg by plane.
Electric trains are more expensive upfront than diesel trains, but they are cheaper to operate and maintain, and they reduce wear on the tracks as they are lighter.
