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PHEVs emit nearly five times greater planet-heating pollution than official figures indicate, according to a new analysis.

Widening Gap Between Official and Real-World Emissions

Statistics reveals that PHEVs emit only 19% lower CO₂ than traditional petrol and diesel vehicles, based on analysis carried out by a non-profit group. This differs sharply with laboratory tests, which suggested a three-quarters reduction in pollution.

Analysts examined information from onboard energy use monitors of 800,000 cars registered in the EU from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are falling,” said a senior analyst involved in the report. “That discrepancy is widening and creates a significant issue. Consequently, PHEVs pollute nearly as heavily as petrol vehicles.”

Key Reasons Behind the Emissions Gap

Analysts attributed the majority of the gap to inflated estimates of the “utility factor” – the percentage of miles travelled in electric mode compared to overall distance. The team determined that just a quarter of travel was completed in electric mode, whereas official assumptions suggested over four-fifths.

Additionally, when operating in EV mode, emission amounts were significantly higher than official estimates. This happened because EV motors were insufficiently powerful sufficient to operate alone, resulting to engines burning gasoline for almost one-third of the distance completed in EV mode.

Regulatory and Economic Consequences

According to calculations, the lowballing of PHEV CO2 output allowed several large carmaker groups to escape over €5bn in penalties between 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ standards.

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

“The bold claims that manufacturers often promote about their plug-in hybrid vehicles are obviously far from the mark,” commented a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are little better than standard petrol and diesel vehicles in terms of energy use, CO₂ emissions, and running costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been brought back into policy discussions as automakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on sales of new combustion engine cars in 2035 has faced intense lobbying from the automotive sector and resistance from EU countries with large automotive manufacturing.

Some senior politicians have proposed PHEVs as a possible “compromise” option to introduce in the legislation.

An external energy policy expert, who was unaffiliated with the research, described the report a “highly valuable contribution” after years in which segments of the car industry claimed there was too little data to accurately evaluate actual emissions.

“The results demonstrate, without question, that the difference in lab and actual PHEV energy use and CO₂ output is much, much larger than for petrol or conventional cars,” the expert said. “All policy changes concerning PHEVs should be implemented with utmost caution and in the light of this data.”