Bus Retrofit Performance Report

Thursday 12th September 2024 Written Statements

[The Secretary of State for Transport (Louise Haigh)]

Today, I am providing an update regarding the retrofitting of buses with selective catalytic reduction—SCR—technology to reduce emissions of nitrogen oxides.

Through a series of trials between 2013 and 2015, the previous Government explored the potential of reducing emissions or improving fuel economy in older buses and other large vehicles through a range of retrofit technologies. Retrofitting SCR technology was found to be the most effective in reducing the levels of NOx emitted from older buses. Allowing for some variation based on the Euro standard of the retrofitted bus, the reduction of NOx using SCR technology in trials averaged around 90%.

The clean vehicle retrofit accreditation scheme—CVRAS—was launched in 2017 to accredit retrofit technologies that could reduce NOx emissions from buses to close to Euro VI levels. Between 2017 and 2019, £64 million was allocated to the clean bus technology fund for bus upgrades and retrofits. A further £31 million was provided to local authorities in the Government’s NO₂ programme. Approximately 9,000 buses in England have been retrofitted with CVRAS-accredited SCR technology.

In 2021, the Government were made aware of new evidence from Scotland suggesting that real-world emission reductions from retrofitted buses were lower than expected. In 2022, a roadside monitoring campaign was commissioned to measure NOx emissions from retrofitted buses in three areas in England, which reported in early 2023. The findings were similar to those in Scotland. Government funding for bus retrofits was paused in April 2023 while further research was carried out to understand the causes of poor performance and assess the scope for improvement.

The research was overseen by the Department for Transport and the Department for Environment, Food and Rural Affairs chief scientific advisers, assisted by an external independent expert group. Today I have placed the bus retrofit performance report, containing the findings of this research, in the Libraries of both Houses. The performance report was commissioned by the Government and finalised in November 2023. In the interest of transparency, I am releasing the report today.

The report concludes that the real-world performance of bus retrofit SCR technology is highly variable, achieving 80% to 90% NOx reductions in some cases, but having a minimal effect in others. There is an average 11% reduction in NOx emissions overall from retrofitted buses, compared with non-retrofitted Euro V buses, which is significantly lower than the 80% reduction anticipated.

The research shows that a number of contributing factors can lead to poor performance, including the incorrect functioning of retrofit systems, the condition of bus engines and low catalyst operating temperatures. Based on these findings, I am announcing today a permanent end to further Government funding for retrofit and the closure of the clean vehicle retrofit accreditation scheme to further accreditations.

Moving forward, we will work with bus operators and retrofit suppliers to encourage a step change in the monitoring and maintenance of retrofit systems to get the best possible performance from the retrofitted buses currently in service. This will include ensuring that buses are providing live data showing retrofit performance, so that operators and depots can prioritise and target essential maintenance on the poorest-performing buses. Providing this data will be a condition of the buses remaining on the list of CVRAS-accredited vehicles.

Air pollution is the biggest environmental threat to human health, and this Government recognise the need to take preventive public health measures to tackle the biggest killers and support people to live longer, healthier lives. We will continue to work closely with the relevant local authorities to identify alternative measures to deliver compliance with legal NO2 limits in the shortest possible time.

[HCWS97]