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Plug-in hybrid electric vehicles produce nearly five times greater planet-heating pollution than lab-reported figures show, according to a new report.

Widening Gap Between Official and Actual Emissions

Data shows that PHEVs release just 19% less CO₂ than conventional petrol and diesel cars, based on research conducted by a non-profit organization. That differs sharply with lab tests, which assumed a 75% reduction in pollution.

Analysts studied information from onboard energy use meters of 800,000 cars sold in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, up from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are decreasing,” stated a senior researcher involved in the report. “This gap is widening and creates a serious problem. As a result, PHEVs pollute almost as much as gasoline vehicles.”

Primary Factors Behind the Discrepancy

Researchers linked most of the gap to overestimates of the “utility factor” – the percentage of kilometers driven in electric mode compared to overall mileage. They determined that only a quarter of driving was completed in electric mode, whereas lab estimates assumed 84%.

Additionally, when operating in electric mode, pollution levels were well above official projections. This happened because electric motors were not strong sufficient to function alone, resulting to combustion motors using fossil fuels for almost a third of the travel covered in electric mode.

Regulatory and Economic Implications

Based on calculations, the underestimation of PHEV emissions enabled four large carmaker companies to escape over €5bn in fines from 2021 and 2023, by falsely simplifying adherence with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs could spend approximately €500 extra annually in running costs than is estimated under lab conditions.

“The bold statements that automakers often promote about their PHEV cars are clearly far from the mark,” commented a transport analyst. “Buyers are being misled into thinking that by buying a PHEV, they are helping the environment and cutting money. Actually, PHEVs are little better than regular gas and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Political Debate and Automotive Lobbying

Hybrid cars have lately been drawn again into political debates as carmakers have pressed the European Union to weaken CO₂ targets. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from EU countries with large car industries.

Some senior officials have proposed plug-in hybrids as a possible “compromise” solution to introduce in the regulation.

One independent energy economics expert, who was not involved with the study, called the report a “very useful addition” after a long period in which segments of the car sector claimed there was too little information to properly evaluate actual CO2 output.

“These findings demonstrate, without question, that the difference between official and real-world PHEV fuel consumption and CO₂ output is significantly greater than for gasoline or conventional vehicles,” they said. “All policy changes concerning PHEVs should be implemented with utmost care and considering that data.”