EU Plug-in Hybrids Emit Six Times More CO2 Than Official Tests Claim
A Transport & Environment analysis reveals a widening gap between laboratory ratings and real-world pollution for PHEVs.
Plug-in hybrid electric vehicles (PHEVs) are emitting significantly more carbon dioxide on the road than official laboratory tests suggest. New data indicates this discrepancy has widened over the last year, undermining official emissions targets and consumer expectations.
An analysis by Transport & Environment (T&E), utilizing European Environment Agency (EEA) data, found that in 2024, real-world PHEV emissions averaged 145g of CO2 per kilometer. This is six times higher than the 24g CO2/km reported in official tests. The gap has grown since 2023, when real-world emissions were 138g compared to a test rating of 28g—a five-fold difference. Notably, real-world emissions increased by 5% between 2023 and 2024, even as official test ratings for these vehicles decreased.
The Utility Factor Gap
The discrepancy stems from how PHEV emissions are calculated. Regulators use "utility factors" to estimate the balance between battery use and combustion engine use. However, T&E's analysis of On Board Fuel Consumption Monitoring (OBFCM) systems across 220,000 vehicles shows that many drivers rarely plug in their cars.
Because these vehicles are not charged as frequently as the models assume, they rely heavily on their internal combustion engines. This results in emissions profiles that closely mirror conventional gasoline cars. While conventional gasoline cars average 169g CO2/km, real-world PHEV usage now sits at 145g CO2/km, far exceeding the idealized laboratory figures.
Implications for the Industry
This gap allows automakers to claim "green" credits for vehicles that pollute nearly as much as traditional combustion engines. Lucien Mathieu, cars director at T&E, described plug-in hybrids as "one of the auto industry’s greatest greenwashing stunts," arguing they are marketed as green solutions while delivering a heavy environmental toll in practice.
Beyond the environmental impact, the data suggests consumers may be misled regarding the actual fuel costs and carbon footprints of their vehicles. By inflating the perceived efficiency of PHEVs, the industry may be delaying the transition to fully electric battery vehicles (BEVs), which do not suffer from this utility-based emissions gap.
What's Next
The findings place pressure on European regulators to reform how hybrid emissions are measured. While the core data from the EEA confirms the trend of increasing real-world pollution, the industry continues to push back against tighter regulations. Observers are now watching whether the EU will implement more stringent monitoring requirements to ensure that official ratings reflect actual driving behavior rather than idealized laboratory conditions.