Enclosed railway stations hosting diesel trains pose a risk to passengers and workers as exhaust emissions reduce air quality, according to an independent study by the University of Cambridge, University of Minnesota and Minnesota State University Mankato, published in September 2015 in the journal Environmental Research Letters.

The researchers evaluated air quality in London Paddington train station over a period of five days and each time found it to be in breach of European limits regarding nitrogen dioxide (NO2) for outdoor air quality. Further comparisons sampling particulate matter (PM2.5), sulphur dioxide (SO2) and NO2 concentrations also found these to be much higher than on the busy Marylebone roadside located nearby.

Paddington station serves 38 million passengers annually, making it the seventh busiest station in the UK. Up to 70% of its trains passing through the station are powered by diesel engines, but many of these are old and thus exempt from the regulations for modern diesel locomotives.

UK railway stations are not required to comply with air quality standards imposed by the EU, despite the fact that eight million passengers pass through them every day. Moreover, British rolling stock has a mean age of 18 years, meaning a sizeable portion was deployed eleven years before EU emissions regulations took effect.

“As a result, diesel trains that operate in enclosed stations have the potential to emit large quantities of pollutants, leading to poor air quality and threatening the wellbeing of frequent travellers and workers,” the study reads.

Globally, railway travel enjoys a positive track record, scoring as one of the greenest modes of transportation available. While the entire transport sector contributes about 22% of global emissions, rail only accounted for 0.8% of this between 1990 and 2009, statistics from the European Environment Agency (EEA) show.

In addition, rail and inland waterways were the only modes that recorded an absolute decrease in energy consumption between 1990 and 2013 within the 33 member countries of the EEA.

But as Railway Gazette group editor in chief Christopher Jackson points out in an editorial, “while rail is by far the most environmentally-friendly form of surface transport, many of the world’s railways are not being used as effectively as they could be. As other modes are steadily improving their environmental credentials, the rail sector must not rest on its laurels.”

Where does the EU stand on rail emissions?

Pollution produced by trains is caused by using diesel engines; electric trains are emission-free at the point of use.

Statistically, about 20% of Europe’s current rail traffic is hauled by diesel locomotives, according to the European Commission. The UK, Greece, Estonia, Latvia and Lithuania are among those highly dependent on diesel traction.

“Statistically, about 20% of Europe’s current rail traffic is hauled by diesel locomotives.”

“While the cumulative number of passengers exposed to diesel emissions within train stations throughout Europe is unknown,” the study states, “there is significant potential risk if train station air quality is poor, given the large number of stations required to serve non-electrified lines, high rail use and passenger time spent within the station.”

Great advances have so far been made in the EEA-33 area, where 53% of the rail network was electrified by 2013, but approximately half of the train lines in Europe remain non-electrified to this day. In the UK, only 41% of train tracks are electrified.

Since Public Health England estimates that 29,000 deaths a year in the UK are caused by air pollution, there are mounting pressures for improvement in this area both at national and EU level.

Legislation setting environmental standards for non-road vehicles powered by diesel engines has been around since 1997. The current EU regulatory framework that applies to train diesel engines is represented by the Stage IIIA and IIIB standards. Upgraded in January 2012, the Stage IIIB standard requires diesel engines greater than 130 kW to reduce the effects on the environment of exhaust emissions, with a focus on particulate matter, nitrogen oxides, hydrocarbons (HC) and carbon monoxide (CO).

New reduction standards and how to achieve them

In December 2015, new reduction goals were outlined as part of the Low Carbon Sustainable Rail Transport Challenge, an initiative spearheaded by the International Union of Railways. The challenge aims for cutbacks of 50% in both energy consumption and CO2 emissions from train operations by 2030 relative to a 1990 baseline, and a total energy reduction of 60% by 2050.

The best way to achieve these cutbacks has already been proven. A four-year project known as Clean European Rail-Diesel (CleanER-D) and led by the European Railway Industry Association dedicated £8.9m between 2009 and 2013 to “develop, improve and integrate emissions reduction technologies for diesel locomotives and rail vehicles”.

The project, which ended in January 2014, researched solutions compliant “with and beyond” the latest IIIB emissions standard and looked at both the potential for new and re-manufactured rolling stock in meeting these challenges.

Although the trials showed that it was possible “to retrofit existing locomotives with configured and compliant engines”, it also concluded that it is “economically and technically challenging for rail operators to replace or retrofit older diesel locomotives to meet tighter emission limits on pollutants”.

The key finding of the project was that “renewal of the fleet is the most feasible and economic way of achieving the EU’s goal of reducing emissions by 2030.”

Innovative alternatives to diesel engines

In the UK, the air quality inside train stations is poorly documented and Parliament admits that “indoor public health standards are neither well understood nor controlled by a specific government agency,” the study notes.

A broad reference within the main Network Rail Safe by Design principles applicable to stations mentions that “air quality shall not be made worse and where possible improved”.

But despite the lack of a legislative framework, the UK rail industry is making advances both through government-funded initiatives and individual projects.

An example of innovation that stands out is the Independently Powered Electric Multiple Unit (IPEMU), the first battery-powered train to start service on the UK rail network after more than 50 years. The train, running between Harwich International and Manningtree stations in Essex, was the result of a partnership between manufacturer Bombardier, train operator Abellio Greater Anglia and Network Rail.

“Indoor public health standards are neither well understood nor controlled by a specific government agency.”

At its launch in January 2015, Network Rail said that “the project could ultimately lead to the development of a whole fleet of battery powered-trains” and that the technology could be used to bridge gaps between electrified parts of the network and areas where electrification proves too expensive.

According to a document published by the Department for Environment Food and Rural Affairs (DEFRA), “a number of train operators and manufacturers have expressed interest in commercialising the technology.”

Similarly, independent company Vivarail wondered why trains shouldn’t have the same filtering systems for their diesel engines as modern cars do. To prove how an efficient diesel particulate filter can be leveraged from automobiles to rail, the company created the D-train, a prototype up-cycled from old rolling stock and fitted with low-emission diesel engines.

The UK’s national electrification programme

On a national level, the Department for Transport has embarked on various electrification programmes.

By far the largest project is a £2.8bn upgrade of the Great Western mainline from London to Cardiff, which will enable the replacement of older diesel locomotives with modern electric trains. Despite an initial deadline set in 2018, Network Rail confirmed that due to uncompleted routes the completion date was pushed back to 2020.

Other government plans include the Intercity Express programme, which promises the introduction of state-of-the-art electric and bi-mode trains on the Great Western Main Line from 2017 and on the East Coast Main Line from 2018.

“The bi-mode version will be able to draw electricity from overhead lines where it is available and switch to low emission diesel engine power where it is not,” a DEFRA draft document explains.

But pressures are mounting to set in place some standards, especially since estimates show that transport will grow to contribute 33% of global CO2 emissions by 2050.

“Policymakers must find ways to provide sufficient rail capacity to meet future demand, including greater use of renewable energy sources,” Jackson writes.

“While there are many steps that the rail sector can take by itself, the process could be made easier by a supportive policy framework and a more level playing field where all modes pay fairly for their externalities, including carbon emissions.”