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Plug-in hybrid electric vehicles release nearly five times greater planet-heating emissions than lab-reported figures show, according to a new report.

Growing Gap Between Official and Real-World CO2 Output

Data shows that PHEVs emit just 19% less CO₂ than traditional gas and diesel vehicles, based on analysis conducted by a advocacy group. That contrasts significantly with laboratory tests, which assumed a three-quarters reduction in pollution.

Analysts studied data from onboard fuel consumption monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” said a lead analyst involved in the study. “That discrepancy is growing and creates a significant problem. As a result, PHEVs pollute almost as much as petrol cars.”

Key Factors Driving the Emissions Gap

Analysts linked the majority of the difference to inflated estimates of the “utility factor” – the percentage of miles driven in battery mode relative to total mileage. The team determined that only 27% of travel was done in EV mode, whereas lab assumptions suggested over four-fifths.

Additionally, when operating in EV mode, pollution levels were significantly higher than official projections. This occurred because electric motors were not strong sufficient to operate alone, resulting to engines using fossil fuels for almost a third of the travel completed in electric mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV emissions allowed four major automaker groups to avoid more than €5bn in fines between 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs would spend about €500 more per year in running expenses than is estimated under laboratory conditions.

“The strong statements that automakers often promote about their PHEV vehicles are clearly far from the mark,” commented a automotive expert. “Buyers are being duped into thinking that by purchasing a PHEV, they are benefiting the environment and saving costs. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and running costs.”

Political Debate and Industry Pressure

Hybrid vehicles have lately been brought back into policy debates as automakers have pressed the European Union to relax CO₂ targets. A proposed ban on new combustion engine vehicles in 2035 has faced heavy pressure from the car sector and opposition from EU countries with significant car industries.

Several senior politicians have proposed plug-in hybrids as a possible “compromise” solution to introduce in the regulation.

One external energy economics expert, who was not involved with the study, called the report a “highly valuable addition” after a long period in which segments of the automotive industry claimed there was insufficient data to properly assess actual CO2 output.

“The results show, beyond any doubt, that the gap between lab and actual PHEV fuel consumption and CO₂ output is much, much larger than for gasoline or conventional cars,” they said. “All policy changes regarding PHEVs should be made with extreme care and considering this data.”