The UK’s Transport Secretary, Louise Haigh has confirmed the government’s decision to permanently end funding for bus retrofit initiatives.
This decision will see the closure of the Clean Vehicle Retrofit Accreditation Scheme (CVRAS).
The shift follows trials, research, and real-world performance reviews where older buses were retrofitted with selective catalytic reduction (SCR) technology, aimed at reducing nitrogen oxide (NOX) emissions.
The History of Bus Retrofits
To address air pollution and reduce NOX emissions from public transport, the UK government has previously supported initiatives to retrofit older buses with SCR technology.
Between 2013 and 2015, the government conducted trials to explore whether retrofitting could improve emissions or fuel economy in older buses. The results indicated that SCR technology was highly effective in reducing NOX emissions, with some trials reporting an impressive average reduction of around 90 percent, depending on the Euro standard of the buses.
To support this initiative, the CVRAS was launched in 2017 to accredit technologies capable of reducing emissions to levels close to Euro VI standards. Government funding between 2017 and 2019 totalled 64 million GBP, allocated through the Clean Bus Technology Fund, with an additional 31 million GBP provided to local authorities under the NO2 programme.
By 2023, around 9,000 buses in England had been retrofitted with CVRAS-accredited SCR technology.
Performance Concerns and Findings
Despite this initial optimism, new evidence surfaced in 2021, casting doubt on the real-world performance of retrofitted buses. Reports from Scotland suggested that the actual reductions in NOX emissions were lower than anticipated.
This prompted the UK government to commission further research in 2022, focusing on three areas in England. Roadside monitoring results, published in early 2023, echoed the Scottish findings, leading to a temporary pause in government funding for bus retrofits.
The Department for Transport (DfT) and the Department for Environment, Food and Rural Affairs (Defra), alongside an independent expert group, oversaw an in-depth review of bus retrofit performance. The findings, now available in the Bus Retrofit Performance Report, revealed variable outcomes. While some buses achieved reductions of 80-90% in NOX emissions, others experienced minimal or no significant improvement.
On average, retrofitted buses achieved only an 11% reduction in NOX emissions compared to non-retrofitted Euro V buses—far below the anticipated 80%.
Reasons for Poor Performance
The report highlighted several factors contributing to the underwhelming results of the SCR retrofitting initiative.
Key issues included:
- Malfunctioning retrofit systems: Some retrofits were not functioning as intended, compromising their effectiveness in reducing emissions.
- Condition of bus engines: Older and poorly maintained engines posed challenges for the proper operation of retrofit technology.
- Low catalyst operating temperatures: SCR technology requires high temperatures to operate effectively, and buses operating at lower temperatures saw reduced performance.
Conclusion of Government Funding
In light of these findings, Haigh has announced a permanent end to government funding for bus retrofitting.
The CVRAS will also be closed to further accreditations, effectively bringing an end to government-supported SCR retrofitting schemes.
However, the government states that it remains committed to working with bus operators and retrofit suppliers to ensure that existing retrofitted buses operate as efficiently as possible. This will include more robust monitoring and maintenance, as well as live performance data from buses to aid in targeting essential maintenance.
