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Plug-in hybrid cars produce almost five times more planet-heating emissions than official data indicate, according to a new analysis.

Widening Discrepancy Between Lab and Real-World Emissions

Data shows that PHEVs release just 19% less CO₂ than conventional gas and diesel vehicles, based on research carried out by a non-profit organization. This differs significantly with laboratory tests, which assumed a three-quarters reduction in emissions.

Researchers examined information from onboard energy use meters of 800,000 cars sold in the EU between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than lab estimates, up from 3.5 times in 2021.

“Real-world emissions are increasing, while official figures are decreasing,” stated a senior analyst participating in the study. “That gap is widening and creates a significant problem. Consequently, PHEVs pollute almost as heavily as petrol cars.”

Key Reasons Behind the Emissions Gap

Analysts attributed most of the difference to inflated estimates of the “utility factor” – the percentage of kilometers driven in electric power relative to overall distance. The team determined that just a quarter of driving was done in EV mode, whereas official assumptions suggested over four-fifths.

Even, when operating in EV mode, pollution levels were significantly higher than lab projections. That occurred because EV motors were insufficiently powerful sufficient to function alone, resulting to engines burning gasoline for almost one-third of the distance covered in electric mode.

Regulatory and Economic Consequences

Based on estimates, the underestimation of PHEV emissions allowed several large automaker companies to avoid over €5bn in fines between 2021 and 2023, by artificially simplifying adherence with European Union fleet-average CO₂ standards.

Additionally, drivers of PHEVs could spend about €500 more annually in running expenses than is assumed under lab conditions.

“The strong statements that automakers often promote about their PHEV cars are clearly way off the mark,” commented a transport analyst. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the planet and cutting money. Actually, PHEVs are only slightly improved than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Political Discussion and Automotive Lobbying

Plug-in hybrid vehicles have recently been drawn again into political debates as automakers have pressed the European Union to relax CO₂ targets. A proposed prohibition on new combustion engine vehicles in 2035 has faced heavy pressure from the car industry and opposition from member states with significant automotive manufacturing.

Several high-level officials have suggested PHEVs as a possible “compromise” solution to include in the regulation.

An external energy economics specialist, who was not involved with the study, called the analysis a “highly valuable addition” after years in which parts of the car sector claimed there was too little data to properly assess real-world emissions.

“These findings show, without question, that the gap in lab and real-world PHEV energy use and CO₂ output is significantly greater than for gasoline or diesel vehicles,” they said. “All regulatory adjustments concerning PHEVs should be made with extreme caution and in the light of this data.”