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Plug-in hybrid cars release almost five times more planet-heating pollution than lab-reported figures show, as per a new report.

Growing Discrepancy Between Lab and Real-World CO2 Output

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

Analysts examined data from onboard energy use monitors of eight hundred thousand vehicles registered in Europe from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, increased from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are decreasing,” said a senior researcher participating in the study. “That discrepancy is widening and creates a significant issue. Consequently, PHEVs pollute almost as heavily as gasoline cars.”

Primary Reasons Behind the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “electric driving share” – the percentage of miles travelled in electric mode compared to total distance. They found that just 27% of driving was done in EV mode, while lab assumptions assumed over four-fifths.

Additionally, when running in EV mode, pollution amounts were significantly higher than lab estimates. This occurred because electric motors were not strong sufficient to operate alone, resulting to combustion motors burning gasoline for almost a third of the distance covered in electric mode.

Regulatory and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output enabled four major automaker groups to escape more than €5bn in penalties from 2021 and 2023, by falsely easing adherence with European Union fleet-average CO₂ standards.

Additionally, drivers of PHEVs could spend about €500 more per year in running expenses than would be estimated under laboratory tests.

“The bold claims that manufacturers like to make about their plug-in hybrid vehicles are obviously far from the mark,” commented a automotive expert. “Buyers are being misled into thinking that by buying a PHEV, they are helping the environment and saving money. Actually, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and operating costs.”

Political Discussion and Automotive Pressure

Plug-in hybrid vehicles have recently been drawn again into political debates as automakers have lobbied the EU to relax CO₂ standards. A proposed prohibition on new internal combustion vehicles in 2035 has faced heavy lobbying from the car sector and opposition from member states with large car industries.

Some senior officials have suggested plug-in hybrids as a potential “flexibility” option to include in the legislation.

One independent energy economics specialist, who was not involved with the study, called the report a “very useful addition” after a long period in which parts of the automotive industry argued there was insufficient information to properly assess actual emissions.

“These findings show, beyond any doubt, that the gap between official and actual PHEV energy use and CO₂ output is significantly greater than for gasoline or conventional vehicles,” the expert said. “Any policy adjustments regarding PHEVs should be made with extreme care and considering this data.”