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Plug-in hybrid electric vehicles emit nearly five times more planet-heating pollution than lab-reported data show, as per a new analysis.

Widening Gap Between Lab and Actual CO2 Output

Data shows that PHEVs emit only one-fifth less CO₂ than traditional gas and diesel vehicles, based on analysis conducted by a advocacy group. This contrasts significantly with laboratory tests, which assumed a three-quarters decrease in pollution.

Researchers studied data from onboard fuel consumption monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, up from 3.5 times in 2021.

“Actual CO2 output are rising, while lab-reported emissions are decreasing,” said a senior analyst participating in the report. “That discrepancy is widening and creates a serious issue. Consequently, PHEVs pollute nearly as heavily as petrol cars.”

Key Factors Driving the Emissions Gap

Researchers attributed most of the gap to overestimates of the “utility factor” – the ratio of miles travelled in battery power compared to overall mileage. They found that just a quarter of driving was completed in electric mode, whereas lab estimates suggested over four-fifths.

Even, when running in EV mode, emission levels were well above lab estimates. That happened because EV motors were insufficiently powerful enough to operate independently, leading to engines burning gasoline for nearly a third of the distance covered in electric mode.

Policy and Financial Consequences

Based on estimates, the underestimation of PHEV emissions enabled several large automaker companies to escape over €5bn in penalties between 2021 and 2023, by falsely easing adherence with European Union average fleet CO₂ targets.

Furthermore, owners of PHEVs could pay approximately €500 more annually in running costs than would be estimated under laboratory tests.

“The strong statements that automakers often promote about their PHEV vehicles are clearly way off the truth,” commented a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting money. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been brought back into policy debates as automakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on sales of new internal combustion cars in 2035 has faced heavy pressure from the car industry and opposition from member states with large automotive industries.

Some high-level politicians have suggested plug-in hybrids as a possible “flexibility” solution to include in the regulation.

One external energy policy specialist, who was unaffiliated with the research, called the report a “highly valuable contribution” after years in which parts of the automotive industry argued there was insufficient data to properly assess actual emissions.

“The results demonstrate, beyond any doubt, that the gap between lab and actual PHEV fuel consumption and CO₂ output is significantly larger than for petrol or conventional cars,” they stated. “Any regulatory changes regarding PHEVs should be made with utmost care and considering that evidence.”