Policy paper

Rail air quality policy statement

Published 26 February 2026

Applies to England

Purpose and scope of statement

This statement sets out a framework for managing and improving air quality on the railway, in line with government priorities. It defines the outcomes and measures the Department for Transport (DfT) expects the rail sector to deliver.

Once established, Great British Railways (GBR) will provide system-wide leadership and oversight for environmental performance, including air quality. It will be accountable for the passenger journey from start to finish, including the management of stations and train fleets.

The statement applies to the mainline passenger railway in England. It covers locations where people may be exposed to air pollution from trains, including:

• stations
• onboard services
• depots
• sidings

It does not apply to Scotland, Wales or Northern Ireland, where rail and air quality policy is devolved.

Rail freight and open access operators are not within the formal scope of this statement, as they operate under separate commercial and regulatory arrangements. However, as their services operate within many of the same locations as the passenger railway, DfT will continue to work collaboratively with these operators. This will help ensure that air quality measures for the passenger network take account of relevant activities and planned improvements.

Introduction

Air pollution affects people across society, with both short-term and long-term exposure linked to a range of health impacts^{[footnote 1][footnote 2]}. Children and older adults are more vulnerable to its effects and people living in low-income areas may experience higher exposure because of where they live or work.

Improving air quality is therefore a government priority. The 10 Year Health Plan for England identifies air pollution as 1 of 5 prevention priorities and recognises the role of cleaner transport in improving public health. The Environmental Improvement Plan 2025 sets out wider ambitions to protect and restore nature, including meeting legally binding air quality targets.  

Air quality on the railway

Rail is one of the greenest ways to travel, connecting people and goods safely and reliably across the country. Compared with other forms of transport, rail contributes a relatively small share of national emissions, accounting for 2% of transport-related particulate matter and 4% of nitrogen oxides (NOₓ).

However, national averages do not reflect the challenges that can arise in specific rail environments. In enclosed spaces, such as station platforms or onboard trains, emissions can accumulate to higher levels than outdoors. The main sources include exhaust emissions from diesel trains, which release NOₓ and particulate matter, as well as particles generated from:

• braking
• wheel-rail contact
• track wear

Addressing these localised emissions is essential to ensure that stations and trains remain clean, comfortable and welcoming environments for passengers and staff.

Station air quality monitoring 

To improve understanding of air quality at mainline stations, the Air Quality Monitoring Network (AQMN) was established by the Rail Safety and Standards Board (RSSB) in 2022 with funding from DfT.

It is the UK’s first dedicated programme for monitoring air quality in railway stations and has collected data at more than 100 locations across England, Scotland and Wales. The network focuses on pollutants most relevant to human health, including nitrogen dioxide (NO2) and particulate matter (PM10 and PM2.5).

Findings to date show that pollutant levels are typically highest at stations where diesel trains operate in enclosed or partially enclosed environments, where emissions disperse less easily. Air quality conditions vary between sites depending on factors such as:

• station layout
• ventilation
• train idling times
• local background pollution

The AQMN uses the UK outdoor annual mean NO2 limit of 40 µg/m³ as an indicator of  where further investigation or mitigation may be required.

In 2022, 35 stations across Great Britain recorded annual mean NO2 levels above this indicator, rising to 47 stations in 2023 as additional locations were included in the network. Although this outdoor air quality limit does not legally apply to indoor or partially enclosed station environments, it provides a reference point to identify locations where targeted action may be needed.

There is currently no overarching legal framework for indoor air quality^{[footnote 3]}, unlike outdoor environments where national objectives and limits apply.

Station operators and duty holders already manage air quality risks as part of their wider health and safety responsibilities^{[footnote 4]}. The AQMN provides complementary environmental monitoring data that supports these arrangements, helping to identify where further assessment or mitigation may be needed.

In response to AQMN findings, train operators and Network Rail have developed air quality improvement plans (AQIPs) for stations where monitoring shows a need for improvement. These plans include:

• measures to reduce emissions at source, such as reducing engine idling and introducing stop-start technology on trains
• actions to improve air circulation and filtration within stations

Onboard air quality monitoring

Alongside station monitoring, a study funded by DfT and carried out by Imperial College London in 2021 measured air quality on 100 passenger journeys across 13 different train classes. The study found that air pollution levels onboard some trains were higher during diesel operations, particularly in tunnels or when trains were idling in stations.

The findings provided important evidence to support action to reduce emissions and improve onboard air quality.

In response, train operators and manufacturers have trialled a range of mitigation measures, including changes to how diesel engines operate to reduce emissions and adjustments to onboard air intake systems. Where these trials have shown positive results, these changes have been introduced across fleets to help deliver cleaner air for passengers and staff.

Building on the evidence  

The station and onboard air quality studies provide the most comprehensive evidence to date on air quality in the railway system. Together, they help identify where action is most needed and where interventions are likely to deliver the greatest benefit. This evidence underpins the outcomes and measures set out in this statement and supports a targeted, proportionate approach to improving air quality for passengers and staff.

Outcome 1: Reduce emissions across the passenger network

Improving air quality across the passenger network requires reducing pollution from train operations.

The most significant long-term benefits will come from decarbonising the railway by phasing out diesel traction, supporting the UK’s legal commitment to reach net zero by 2050. Alongside this transition, practical operational measures can reduce emissions from existing trains and improve efficiency in the near to medium term.

How this outcome will be achieved

Switching to cleaner traction

Operators are introducing cleaner, lower emission trains, including bi-mode units that can switch to electric power on electrified routes, reducing reliance on diesel.

Work is also progressing on tri-mode trains, which can operate using diesel, electricity or battery power. This allows zero-emission operation when entering or leaving stations. TransPennine Express has successfully trialled this technology and Grand Central plans to introduce tri-mode trains into service by 2028.

The government is investing in electrification schemes such as the TransPennine Route Upgrade and working with Network Rail to identify where further electrification could deliver the greatest benefits.

DfT is also supporting the development of battery-powered trains, including through the fast charge trial with Great Western Railway. Together, these initiatives will support improvements in:

• air quality
• decarbonisation
• operational efficiency

Minimising diesel idling

Managing diesel engine idling is one of the most effective ways to reduce emissions from existing diesel rolling stock.

Some idling is unavoidable, for example, to maintain braking systems or ensure reliable restarts. However, all diesel train operators are expected to work towards developing and implementing idling reduction plans in line with RSSB’s 2025 Good practice guide on reducing emissions from idling diesel trains. 

The guide sets out approaches to identifying and reducing avoidable idling, using data to understand when and why engines are left running, and addressing operational factors such as platform allocation and timetable planning. This includes opportunities to minimise train dwell times where this can be done safely and feasibly.

Operators are expected to prioritise action, where reducing idling can improve air quality and reduce noise for passengers and nearby communities, at:

• stations
• depots
• sidings

Driving more efficiently     

Driving practices have a direct impact on fuel use and emissions. Techniques such as smoother acceleration and coasting can reduce fuel consumption by around 5 to 10%^{[footnote 5]}.

Supported by technologies such as Driver Advisory Systems, eco-driving can reduce fuel costs and improve local air quality. Operators are expected to support and promote efficient driving practices as part of their existing emissions reduction plans.

Exploring in-service emissions testing

Unlike road vehicles, diesel trains are not currently subject to emissions testing once in service, even though performance can change over time.

RSSB is assessing the technical feasibility of introducing in-service emissions testing, with findings expected in mid-2026. These finding will be reviewed by the rail sector and DfT to determine next steps. If feasible, regular in-service testing could provide additional assurance that trains continue to meet emissions standards and operate efficiently throughout their service life.

Outcome 2: strengthen air quality management at stations

Improving air quality in stations requires a clear, coordinated management framework that brings together data, planning, and delivery.

Outcome 2 focuses on strengthening this framework so that emissions are managed effectively and consistently across stations, and progress can be monitored over time.

How this outcome will be achieved

Consolidating station air quality plans

Air quality improvement plans (AQIPs) are an important mechanism for managing air quality at stations where monitoring shows a need for improvement. Train operators and Network Rail are required to produce AQIPs to set out measures and demonstrate progress in response to AQMN findings, but these plans currently reflect individual organisational responsibilities.

To support more coordinated delivery, a single, consolidated station air quality plan will be developed for each of the stations identified through the AQMN as requiring further investigation.

These plans will bring together measures from existing AQIPs, assess their effectiveness, and identify where further action may be required. This will include using future air quality modelling, where appropriate, to understand how conditions are expected to change over time.

Each plan will take a holistic view of station environments, considering impacts on both passengers and staff. Where relevant, plans will also incorporate input from open access and freight operators.

Local authorities will be engaged where stations are located within clean air zones or air quality management areas, supporting co-ordination with wider local clean air priorities. This may include coordinated action on issues such as reducing taxi idling and sustainable travel to and from stations.

At larger or more complex locations, taskforces are expected to be established to bring together organisations across the rail sector to coordinate implementation and address delivery challenges. RSSB will provide technical guidance, data and analytical tools to support effective plan development and delivery.

All consolidated station air quality plans are expected to be in place by the end of 2026. Outputs will be published in an accessible format to support transparency and public understanding.

Long-term station monitoring

DfT is investing £1 million to extend the AQMN until at least 2030. This will provide a long-term evidence base to track changes in air quality over time and assess the effectiveness of measures implemented at stations. Annual reports will continue to provide transparent, publicly available information on progress.

Outcome 3: Improve understanding of rail air quality

Evidence on rail air quality has grown significantly in recent years, largely through research and monitoring delivered by the rail sector. However, further work is needed to understand how different rail environments influence people’s exposure to air pollution.

Outcome 3 focuses on strengthening this understanding so that future air quality management is informed by the best available evidence.

How this outcome will be achieved

Building the evidence base

DfT is working with the UK Health Security Agency, RSSB and academic experts to improve understanding of how air quality in stations and onboard trains affects people’s exposure to pollutants.

This growing evidence base will support proportionate evidence-based decisions on future monitoring and mitigation, helping to target action where it can deliver the greatest benefit.

New onboard air quality research

DfT is funding a new study of onboard air quality across a range of traction types, including:

• modern diesel trains
• bi-mode trains
• tri-mode trains

The study, due to complete in 2026, builds on Imperial College London’s 2021 research by revisiting trains where mitigation measures have been introduced, to assess whether levels of NO2 and particulate matter have improved.

The project will also trial handheld monitoring devices to support future data collection. This work will help ensure that evidence on onboard air quality remains current, robust, and relevant to the trains in operation today.

Open data for transparency

Alongside publishing annual AQMN reports for stations, RSSB is developing a public data portal to provide open access to rail air quality data.

Each data release will include a plain language summary explaining key trends in an accessible way. This transparency will support public understanding and give local authorities and other stakeholders clear insight into air quality on the railway and how it is being monitored and managed.

How delivery will be monitored and reviewed

Delivery of the outcomes set out in this statement will be led by the rail sector, including Network Rail and train operators. Once established, GBR will provide system-wide leadership on air quality. DfT will continue to provide policy oversight and support, while the Office of Rail and Road fulfils its regulatory role.

Progress will be monitored through the Stations AQMN and new onboard air quality research, which will assess trends in air quality and public exposure. RSSB will continue to provide technical analysis, data management and analytical support.

Findings from this monitoring and research will be published through annual reports and a public data portal. This will:

• support transparency
• demonstrate progress over time
• help inform future decisions on air quality management across the passenger railway

1. Chief Medical Officer (2022). CMO annual report: air pollution.  ↩

2. Committee on the Medical Effects of Air Pollutants (COMEAP) (2022). Cognitive decline, dementia and air pollution.  ↩

3.  Also see the Committee on the Medical Effects of Air Pollutions (COMEAP) (2025). COMEAP response to Air Quality Expert Group (AQEG) report on indoor air quality  ↩

4. See the Health and Safety at Work etc. Act (1974) and Control of substances hazardous to health regulations (COSHH) (2002)  ↩

5.  Rail Partners (2024). Eco train driving and traction energy management guidance note (RP-OPS-GN-17). ↩