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Plug-in hybrid cars produce nearly 5x more planet-heating emissions than official data show, according to a new analysis.

Widening Discrepancy In Lab and Actual CO2 Output

Data shows that PHEVs release only one-fifth less CO₂ than conventional gas and diesel vehicles, according to analysis conducted by a advocacy group. That differs significantly with laboratory estimates, which suggested a 75% decrease in pollution.

Analysts studied information from in-vehicle fuel consumption meters of 800,000 cars registered in the EU from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, up from 3.5 times in 2021.

“Actual emissions are increasing, while official emissions are falling,” stated a lead analyst participating in the study. “This gap is growing and creates a serious problem. As a result, PHEVs emit nearly as heavily as gasoline vehicles.”

Key Reasons Driving the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in electric mode relative to overall mileage. The team determined that only a quarter of driving was done in EV mode, while lab estimates suggested 84%.

Even, when operating in EV mode, pollution levels were significantly higher than official estimates. This happened because EV motors were not strong enough to function alone, leading to engines burning fossil fuels for almost one-third of the travel completed in electric mode.

Regulatory and Financial Consequences

Based on estimates, the underestimation of PHEV emissions enabled four large automaker companies to avoid more than €5bn in fines between 2021 and 2023, by falsely easing adherence with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs could pay about €500 extra annually in operating costs than would be assumed under lab tests.

“The strong claims that manufacturers often promote about their PHEV vehicles are clearly way off the truth,” commented a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are only slightly better than standard gas and diesel cars in terms of fuel use, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have recently been drawn again into political discussions as automakers have lobbied the European Union to relax CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced intense lobbying from the automotive sector and opposition from member states with significant car industries.

Several senior politicians have proposed PHEVs as a possible “flexibility” option to include in the regulation.

One independent energy policy expert, who was not involved with the research, described the report a “highly valuable contribution” after a long period in which parts of the automotive sector argued there was too little data to properly assess real-world emissions.

“These findings demonstrate, beyond any doubt, that the difference in official and real-world PHEV fuel consumption and CO₂ output is much, much greater than for petrol or conventional cars,” the expert stated. “Any policy changes regarding PHEVs should be made with extreme care and in the light of this data.”