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Plug-in hybrid cars release almost five times more planet-heating pollution than lab-reported data indicate, as per a recent report.

Growing Gap Between Lab and Actual CO2 Output

Data reveals that PHEVs release only one-fifth lower CO₂ than conventional gas and diesel vehicles, based on analysis conducted by a non-profit organization. That contrasts sharply with lab tests, which assumed a 75% reduction in pollution.

Researchers studied data from in-vehicle energy use monitors of eight hundred thousand vehicles registered in Europe between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from three and a half times in 2021.

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

Key Reasons Driving the Emissions Gap

Researchers linked most of the gap to overestimates of the “electric driving share” – the percentage of miles driven in electric mode relative to total distance. The team determined that only a quarter of driving was done in EV mode, while lab estimates assumed over four-fifths.

Additionally, when running in EV mode, pollution amounts were significantly higher than official projections. That occurred because electric motors were not strong sufficient to operate alone, leading to combustion motors burning fossil fuels for almost one-third of the distance covered in EV mode.

Regulatory and Economic Implications

According to estimates, the underestimation of PHEV CO2 output enabled several large automaker companies to avoid more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs could pay about €500 more annually in running costs than would be estimated under laboratory conditions.

“The bold statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the truth,” stated a transport analyst. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are only slightly better than regular gas and diesel cars in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Debate and Industry Lobbying

Hybrid vehicles have recently been brought again into policy debates as automakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and opposition from EU countries with large car industries.

Some senior officials have suggested plug-in hybrids as a possible “compromise” option to include in the regulation.

An external energy policy specialist, who was not involved with the study, described the report a “highly valuable addition” after a long period in which segments of the car sector argued there was insufficient information to accurately assess real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the gap between lab and real-world PHEV fuel consumption and CO₂ output is significantly larger than for gasoline or diesel cars,” they said. “Any policy adjustments concerning PHEVs should be implemented with extreme caution and considering that evidence.”