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Plug-in hybrid cars produce nearly five times more planet-heating pollution than lab-reported data show, as per a new report.

Widening Gap Between Lab and Actual CO2 Output

Data shows that PHEVs release only 19% less CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a non-profit organization. This differs sharply with lab estimates, which suggested a three-quarters reduction in emissions.

Researchers studied information from in-vehicle fuel consumption meters of 800,000 vehicles registered in Europe from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, up from three and a half times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” stated a lead analyst involved in the report. “That gap is widening and poses a significant issue. Consequently, PHEVs pollute almost as heavily as gasoline cars.”

Primary Factors Driving the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the ratio of kilometers travelled in battery power compared to total mileage. They found that just a quarter of travel was done in electric mode, whereas lab assumptions suggested 84%.

Additionally, when operating in electric mode, emission levels were well above lab estimates. This happened because EV motors were not strong sufficient to operate alone, resulting to combustion motors burning gasoline for nearly one-third of the distance completed in electric mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV emissions allowed four large automaker groups to escape more than €5bn in penalties from 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs could spend about €500 more per year in running expenses than is assumed under lab tests.

“The bold claims that manufacturers like to make about their plug-in hybrid cars are obviously way off the truth,” commented a transport expert. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the environment and saving costs. Actually, PHEVs are only slightly improved than standard gas and diesel vehicles in terms of energy consumption, CO₂ production, and running expenses.”

Policy Discussion and Industry Lobbying

Hybrid cars have recently been drawn back into political debates as carmakers have pressed the European Union to relax CO₂ targets. A planned ban on new internal combustion cars in 2035 has faced heavy pressure from the automotive industry and opposition from EU countries with significant car manufacturing.

Some senior politicians have suggested plug-in hybrids as a potential “compromise” option to introduce in the regulation.

One independent energy economics expert, who was not involved with the study, described the analysis a “highly valuable addition” after a long period in which parts of the car industry argued there was too little information to properly evaluate actual emissions.

“These findings show, without question, that the difference in lab and actual PHEV fuel consumption and CO₂ emissions is much, much larger than for gasoline or conventional vehicles,” the expert stated. “All regulatory adjustments concerning PHEVs should be made with utmost care and in the light of that evidence.”