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PHEVs emit almost 5x more planet-heating emissions than official data show, according to a new report.

Widening Gap Between Lab and Real-World CO2 Output

Data shows that PHEVs release just one-fifth less CO₂ than traditional petrol and diesel cars, according to analysis conducted by a advocacy organization. This differs significantly with lab tests, which suggested a three-quarters decrease in pollution.

Researchers studied information from in-vehicle energy use monitors of eight hundred thousand vehicles registered in the EU from 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” stated a lead researcher participating in the report. “This gap is growing and creates a serious issue. Consequently, PHEVs pollute nearly as heavily as gasoline cars.”

Key Reasons Driving the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “utility factor” – the ratio of kilometers driven in battery power relative to overall distance. The team determined that only 27% of driving was completed in EV mode, whereas lab assumptions assumed over four-fifths.

Even, when operating in electric mode, pollution amounts were well above lab estimates. This happened because EV motors were insufficiently powerful sufficient to function alone, leading to combustion motors using gasoline for nearly one-third of the travel covered in EV mode.

Regulatory and Financial Consequences

Based on calculations, the underestimation of PHEV CO2 output enabled four large automaker groups to avoid over €5bn in fines between 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs would pay about €500 extra annually in operating costs than is estimated under lab conditions.

“The strong statements that automakers like to make about their plug-in hybrid cars are obviously way off the truth,” stated a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the planet and saving money. In reality, PHEVs are only slightly better than regular petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and running expenses.”

Political Debate and Automotive Lobbying

Hybrid vehicles have lately been drawn back into policy discussions as carmakers have pressed the European Union to relax CO₂ standards. A proposed ban on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive sector and opposition from EU countries with large automotive manufacturing.

Several high-level officials have suggested plug-in hybrids as a possible “flexibility” solution to include in the legislation.

An external energy economics expert, who was not involved with the study, described the analysis a “highly valuable addition” after years in which parts of the car industry claimed there was too little data to properly assess real-world emissions.

“The results show, without question, that the gap between official and actual PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel vehicles,” they stated. “Any policy changes regarding PHEVs should be implemented with utmost caution and in the light of this data.”