Real-World CO2 Emissions of Plug-In Hybrid Vehicles: European Assessment Using On-Board Fuel Consumption Monitoring Data

This study presents a large-scale analysis of real-world plug-in hybrid electric vehicle (PHEV) performance using On-Board Fuel Consumption Monitoring (OBFCM) data, a mandatory European Union system that records in-use fuel consumption and CO2 emissions. Plug-in hybrid electric vehicles are critical to the EU’s decarbonization strategy, yet their real-world climate benefits remain uncertain. Using OBFCM data from 457,303 vehicles monitored between 2021 and 2023, the analysis reveals a profound discrepancy between official test values and actual on-road use. The mean real-world CO2 emissions were 138 g/km, compared to a test cycle average of 46 g/km, resulting in a regulatory gap of approximately 300%—significantly higher than for other vehicle types. Performance varied substantially across manufacturers, with gaps ranging over 200 percentage points. Contrary to expectations, larger battery capacity correlated with a wider performance gap. Real-world electric driving averaged only 45.5% of distance, far below regulatory assumptions. This gap has grown wider each year, indicating that test cycle optimization is outpacing real-world efficiency gains. Policy scenario modeling indicates that reducing the test-to-real-world gap could yield substantial CO2 savings, underscoring the need to incorporate real-world monitoring and revisit test assumptions when evaluating PHEV climate impacts.