Executive Summary
An Empa study shows that retrofitting existing diesel buses to electric operation could accelerate the complete electrification of the European bus fleet by approximately 15 years. So-called E-retrofitting is technically and economically feasible and causes 20–50 percent less environmental impact than the production of new electric buses. Bus operators could expand public transport services through cost savings without requiring additional infrastructure. Currently, only just under three percent of all European buses operate electrically; without measures, electrification would take until 2055 – after the European net-zero target of 2050.
People
- Harald Desing (Empa, Department of Technology and Society)
Topics
- Transport transition and electrification
- Sustainable mobility
- Circular economy and resource conservation
- Climate protection and net-zero targets
Clarus Lead
The pace of electrification in European bus transport risks missing climate targets: at constant fleet size and with a pure new purchase approach, achieving 95 percent electric buses is delayed until 2055 – five years after the net-zero target. The retrofitting approach solves this timing problem through radical simplification: instead of fleet renewal, existing hardware is reused, which reduces raw material consumption and enables cost savings for bus operators. The strategy also addresses the global sustainability gap – currently, retired European buses are exported to countries with weaker emission standards and continue to run on diesel there for decades.
Detailed Summary
The retrofit works technically by replacing the engine and gearbox with electric motors and installing batteries instead of exhaust systems and diesel tanks. Auxiliary drives for air conditioning, braking systems, and power steering can be converted to small electric motors. With standardized retrofit kits, a single conversion takes only a few days. The removed parts consist mainly of steel and aluminum and are recyclable.
The economic advantage lies in flexibility: fleet operators do not have to wait for the end of the 20-year lifespan but can retrofit at any time. This often even extends the overall lifespan, since modern emission standards (particulate matter, noise) are met while the body and interior continue to be used. The saved costs can either increase the operator's margin or be invested in fleet expansion – without requiring major infrastructure construction.
The Empa study, published in the EU project «CircEUlar», emphasizes the standardization opportunity: unlike the variety of cars, city buses have only a few model series in large quantities, which enables cost-effective retrofit kits. Charging infrastructure could be partially realized via existing overhead lines, which allows additional cost savings through smaller batteries. The researcher sees potential also for truck retrofitting and other regions, but warns against premature generalizations without further analysis.
Key Statements
- E-retrofitting accelerates European bus fleet electrification by 15 years and achieves net-zero targets on time
- Retrofit causes 20–50 percent less environmental impact than new construction and prevents export of old diesel buses
- Standardization and rapid conversion times (a few days) enable cost-effective fleet transformation without operational interruption
Critical Questions
Evidence/Source Validity: The study focuses on European city buses – how representative are the cost savings and conversion times for heterogeneous fleets in countries with different maintenance standards?
Conflicts of Interest: What incentives do bus operators have today to retrofit existing vehicles rather than replace them if new purchase subsidies are more attractive?
Causality/Alternatives: To what extent is the 15-year acceleration achieved through retrofitting itself or through the assumption that operators would act faster?
Feasibility/Risks: What technical and regulatory hurdles must be overcome for standardization of retrofit kits, and who bears liability risks for conversions?
Infrastructure Dependency: The study excludes charging infrastructure – how realistic is the assumption that overhead lines are widely available or can be retrofitted?
Scaling/Cost Dynamics: How stable do the 20–50 percent savings remain with mass production of retrofit kits, and what economies of scale are required?
References
Primary Source: Switzerland-EU Package (Bilateral III) – Federal Council Press Release
Supplementary Sources:
- H. Desing: «E-retrofitting can accelerate Europe's bus fleet electrification by 15 years» – Environmental Research: Infrastructure and Sustainability (2026); doi.org/10.1088/2634-4505/ae464b
- Empa – Technology and Society
Verification Status: ✓ 30.06.2026
This text was created with the support of an AI model. Editorial Responsibility: clarus.news | Fact-Check: 30.06.2026