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Plug-in hybrid electric vehicles release almost 5x greater planet-heating emissions than official data indicate, according to a recent report.

Widening Gap In Lab and Real-World Emissions

Data reveals that PHEVs release only one-fifth less CO₂ than traditional gas and diesel cars, according to research carried out by a advocacy organization. This differs significantly with laboratory tests, which assumed a three-quarters reduction in emissions.

Analysts studied data from in-vehicle fuel consumption monitors of 800,000 cars registered in Europe between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than lab figures, increased from three and a half times in 2021.

“Actual CO2 output are rising, while lab-reported emissions are falling,” stated a senior analyst participating in the report. “This discrepancy is widening and poses a significant issue. Consequently, PHEVs emit almost as heavily as petrol vehicles.”

Primary Reasons Driving the Discrepancy

Researchers attributed most of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in battery mode compared to overall mileage. They found that just a quarter of travel was done in EV mode, whereas lab assumptions suggested over four-fifths.

Additionally, when running in electric mode, emission amounts were well above lab estimates. That occurred because electric motors were insufficiently powerful sufficient to function alone, leading to engines using gasoline for almost a third of the travel completed in EV mode.

Policy and Economic Consequences

Based on estimates, the underestimation of PHEV emissions allowed four large automaker groups to avoid over €5bn in fines from 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ standards.

Additionally, drivers of PHEVs could spend about €500 more per year in operating expenses than is assumed under lab conditions.

“The strong claims that manufacturers like to make about their PHEV cars are clearly far from the mark,” stated a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of energy consumption, CO₂ production, and operating costs.”

Policy Debate and Automotive Pressure

Plug-in hybrid vehicles have lately been brought back into policy discussions as carmakers have lobbied the EU to relax CO₂ standards. A planned ban on new internal combustion cars in 2035 has faced intense lobbying from the automotive sector and resistance from member states with large car industries.

Several high-level politicians have suggested plug-in hybrids as a possible “compromise” option to introduce in the regulation.

An independent energy economics expert, who was unaffiliated with the study, described the analysis a “very useful contribution” after a long period in which segments of the car sector claimed there was insufficient data to accurately assess real-world CO2 output.

“These findings show, beyond any doubt, that the gap in official and real-world PHEV energy use and CO₂ emissions is significantly larger than for petrol or diesel vehicles,” the expert said. “All policy changes regarding PHEVs should be made with extreme caution and in the light of this evidence.”