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Plug-in hybrid cars emit nearly five times greater planet-heating emissions than lab-reported figures indicate, according to a new analysis.

Growing Gap Between Lab and Real-World Emissions

Statistics shows that PHEVs emit only one-fifth less CO₂ than conventional petrol and diesel vehicles, according to research carried out by a advocacy group. This contrasts sharply with lab estimates, which assumed a 75% decrease in pollution.

Researchers studied data from onboard energy use meters of 800,000 cars sold in the EU from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” stated a senior analyst participating in the study. “That gap is widening and creates a significant problem. As a result, PHEVs emit almost as heavily as petrol vehicles.”

Primary Factors Driving the Discrepancy

Analysts attributed most of the gap to overestimates of the “utility factor” – the ratio of kilometers travelled in electric mode compared to total distance. The team found that only 27% of driving was completed in EV mode, whereas official estimates suggested 84%.

Additionally, when running in EV mode, pollution levels were significantly higher than lab estimates. This occurred because electric motors were not strong enough to function independently, leading to combustion motors using gasoline for almost one-third of the distance completed in electric mode.

Policy and Economic Consequences

According to estimates, the underestimation of PHEV emissions allowed several large carmaker companies to escape over €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with EU average fleet CO₂ targets.

Additionally, owners of PHEVs would spend approximately €500 extra per year in running costs than would be estimated under lab tests.

“The strong claims that manufacturers often promote about their PHEV cars are clearly far from the truth,” commented a transport expert. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are only slightly improved than standard gas and diesel cars in terms of fuel use, CO₂ production, and operating expenses.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have recently been drawn back into political debates as automakers have lobbied the EU to weaken CO₂ standards. A proposed prohibition on new internal combustion vehicles in 2035 has faced heavy pressure from the car industry and opposition from EU countries with significant automotive manufacturing.

Some senior officials have suggested PHEVs as a possible “flexibility” solution to introduce in the regulation.

An independent energy policy expert, who was unaffiliated with the research, described the analysis a “very useful contribution” after a long period in which segments of the car industry claimed there was too little data to accurately evaluate actual CO2 output.

“The results demonstrate, beyond any doubt, that the difference in lab and actual PHEV fuel consumption and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert said. “All regulatory adjustments regarding PHEVs should be implemented with extreme care and considering this data.”