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Plug-in hybrid electric vehicles emit almost five times greater planet-heating pollution than lab-reported data indicate, according to a recent report.

Growing Gap Between Official and Actual Emissions

Statistics reveals that PHEVs emit just one-fifth less CO₂ than conventional gas and diesel vehicles, according to analysis carried out by a advocacy organization. That differs sharply with lab estimates, which suggested a 75% decrease in pollution.

Analysts studied data from in-vehicle energy use meters of 800,000 cars registered in the EU between 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, increased from 3.5 times in 2021.

“Actual emissions are increasing, while official figures are falling,” said a lead researcher participating in the study. “That discrepancy is growing and poses a serious issue. Consequently, PHEVs pollute almost as heavily as gasoline vehicles.”

Key Factors Driving the Emissions Gap

Researchers linked most of the difference to overestimates of the “electric driving share” – the percentage of miles travelled in electric mode compared to overall mileage. The team found that just 27% of travel was completed in EV mode, while official assumptions suggested over four-fifths.

Even, when running in electric mode, emission amounts were significantly higher than lab estimates. That happened because electric motors were not strong sufficient to operate independently, resulting to combustion motors burning gasoline for almost a third of the travel completed in electric mode.

Policy and Financial Consequences

According to calculations, the lowballing of PHEV emissions enabled several large carmaker groups to avoid more than €5bn in fines from 2021 and 2023, by artificially simplifying adherence with EU average fleet CO₂ targets.

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

“The strong statements that manufacturers often promote about their plug-in hybrid cars are clearly way off the mark,” commented a automotive analyst. “Buyers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are little improved than standard gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running costs.”

Policy Debate and Industry Pressure

Plug-in hybrid cars have recently been brought back into policy discussions as automakers have lobbied the European Union to weaken CO₂ targets. A planned prohibition on sales of new internal combustion vehicles in 2035 has faced heavy pressure from the car sector and opposition from EU countries with significant car manufacturing.

Several senior officials have suggested plug-in hybrids as a potential “flexibility” option to introduce in the regulation.

One external energy policy specialist, who was not involved with the study, described the report a “highly valuable contribution” after a long period in which segments of the car sector argued there was insufficient information to properly evaluate actual CO2 output.

“The results show, without question, that the difference in official and real-world PHEV fuel consumption and CO₂ output is significantly greater than for gasoline or conventional vehicles,” they said. “Any policy adjustments concerning PHEVs should be made with utmost care and considering this data.”