Plug-in hybrid cars (PHEVs) emit almost five times more CO2 onto the road than declared in their registration documents. This is what a new analysis by Transport & Environment (T&E), the European organization for the decarbonisation of transport, claims, which examined the real consumption data of 127,000 vehicles registered in 2023.
The numbers of the emission gap
According to the study, based on data from the European Environment Agency, PHEVs (Plug-in Hybrid Electric Vehicles) emit on average 135 grams of CO2 per kilometer in real use, compared to the approximately 30 grams declared in the official WLTP tests. A value that is dangerously close to the average 166 grams of traditional petrol and diesel cars, with a difference of just 19%.
The discrepancy arises from the difference between the conditions simulated in the approval tests and the daily use of the vehicles. The official tests assume optimal use of the electrical component which in reality rarely occurs, with batteries often not charged and routes that frequently require the intervention of the combustion engine.
The paradox of the electric mode
A particularly significant piece of data concerns the behavior of plug-in hybrids even when traveling in fully electric mode. The data shows an average consumption of 3 liters of petrol per 100 kilometres, which translates into 68 grams of CO2 per kilometre, more than eight times the value indicated in official tests.
The phenomenon is explained by the limited power of the electric motors installed on these vehicles. In situations of high speed or on uphill routes, the system automatically activates the combustion engine to provide the necessary power. On average, the combustion engine contributes around a third of the distance traveled even when the driver selects electric mode.
The economic impact for motorists
The differences between declared and actual consumption translate into significant additional costs for those who drive these vehicles. According to the analysis, an average motorist spends around 500 euros more per year on fuel and charging than expected, a 50% increase on expected costs.
Added to this is the higher purchase price. Bloomberg Intelligence indicates that in 2025 the average selling price of a plug-in hybrid in Germany, France and the United Kingdom will stand at 55,700 euros, around 15,200 euros more than the average cost of a battery electric car.
The paradox of larger batteries
Counterintuitively, PHEVs with greater electric range exhibit higher emissions. Models with a range of more than 75 kilometers emit more CO2 on average than those with a range between 45 and 75 kilometres. The additional weight of larger batteries increases both fuel consumption when the combustion engine is running and the energy required in electric mode.
Among the manufacturers analyzed, Mercedes-Benz has the largest gap between official and real emissions, with average values 494% higher. The GLE-Class model records the highest deviation, with real emissions 611% higher than those declared. The other main European producers show real emissions about three times higher than official data.
The ongoing regulatory debate
The issue takes on particular relevance in the context of the European debate on the energy transition of the automotive sector. The automotive industry is asking the European Union to review the “utility factors”, the corrective measures introduced to progressively align the evaluation of PHEV emissions with real data. Manufacturers would also like to be able to continue selling plug-in hybrids even after 2035, the expected date for the cessation of combustion engines.
Andrea Boraschi, director of T&E Italia, defines plug-in hybrids as “one of the biggest bluffs in automotive history”, underlining how ten years after their launch these vehicles continue to fail to keep their promises in terms of emissions reduction.
The discussion touches on the principle of “technological neutrality” often invoked by the industry, according to which all technologies should compete on an equal footing on the path to decarbonisation. The data presented suggests, however, that considering plug-in hybrids as zero-emission vehicles could slow down investments in pure electric technologies, considered more effective in reducing emissions.
The debate remains open as Europe prepares to overhaul automotive emissions regulations, with significant implications for the continent’s industry, consumers and climate goals.
