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Plug-in hybrid cars emit nearly 5x more planet-heating emissions than lab-reported data indicate, according to a recent report.

Widening Gap In Lab and Real-World Emissions

Data reveals that PHEVs release just 19% lower CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a non-profit group. That contrasts significantly with lab estimates, which suggested a three-quarters reduction in emissions.

Researchers examined data from in-vehicle energy use meters of eight hundred thousand cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, increased from three and a half times in 2021.

“Actual emissions are rising, while official figures are decreasing,” said a lead analyst participating in the study. “This gap is widening and creates a serious problem. Consequently, PHEVs pollute nearly as heavily as petrol vehicles.”

Primary Reasons Driving the Emissions Gap

Analysts linked most of the gap to overestimates of the “electric driving share” – the ratio of kilometers travelled in electric mode compared to total mileage. They found that just a quarter of driving was done in EV mode, while lab estimates suggested over four-fifths.

Additionally, when operating in EV mode, emission amounts were significantly higher than lab estimates. That occurred because electric motors were insufficiently powerful enough to operate independently, resulting to engines using fossil fuels for almost one-third of the distance completed in EV mode.

Regulatory and Economic Implications

Based on calculations, the lowballing of PHEV emissions enabled four large carmaker companies to avoid over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs would spend approximately €500 more annually in running costs than is assumed under lab tests.

“The bold claims that automakers often promote about their plug-in hybrid cars are clearly far from the truth,” commented a transport analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and operating costs.”

Policy Discussion and Automotive Pressure

Plug-in hybrid cars have recently been drawn back into political debates as carmakers have pressed the EU to weaken CO₂ standards. A planned prohibition on sales of new internal combustion vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from EU countries with large car manufacturing.

Several high-level politicians have proposed PHEVs as a potential “flexibility” solution to include in the legislation.

One external energy economics specialist, who was not involved with the research, described the analysis a “very useful addition” after years in which segments of the automotive industry argued there was too little data to properly evaluate real-world emissions.

“These findings demonstrate, without question, that the gap in lab and actual PHEV energy use and CO₂ output is significantly larger than for gasoline or diesel vehicles,” they said. “All policy changes regarding PHEVs should be made with extreme caution and in the light of that evidence.”