Report: Plug-in hybrids emit nearly as much CO2 as petrol cars, real-world data shows

A new analysis of onboard fuel data from 800,000 plug-in hybrid electric vehicles (PHEVs) registered in Europe between 2021 and 2023 finds that real-world CO2 emissions are far higher than lab estimates. The study shows PHEVs emit about 4.9 times more CO2 in everyday use than official figures suggest, narrowing the emissions gap with conventional petrol cars to roughly 19% — not the 75% advantage reported by laboratory tests.

Researchers attribute the discrepancy mainly to an overly optimistic assumption about how often PHEVs run in electric mode. Official lab estimates assume an 84% share of electric driving; the real-world figure is just 27%. That means most PHEV miles are powered by combustion engines, and even when in electric mode many PHEVs still rely on the petrol engine for a significant share of power.

• Dataset: onboard fuel meters from ~800,000 PHEVs in Europe (2021–2023).
• Real-world electric-driving share: ~27% vs official 84%.
• Real-world CO2: 4.9× higher than lab-based expectations.
• Additional fuel cost to drivers: about $582 more than official estimates.
• Estimated extra CO2: ~52 million tonnes above reported figures; carmakers avoided an estimated $5.8 billion in fines (2021–2023) due to underestimated PHEV emissions.

Contributing factors include limited charging convenience (PHEVs often lack fast charging), electric motors that cannot handle all driving conditions on their own, and testing methodologies that overstate electric usage. Major manufacturers such as Volkswagen, Mercedes-Benz and BMW have been prominent sellers of PHEVs in Europe; the report suggests fleet emission targets were met in part because PHEV lab numbers were overly favorable.

For more details, see the full coverage: Engadget coverage of the report.

The findings raise important questions about the role of PHEVs in decarbonizing transport and whether policy and testing frameworks should be adjusted to reflect real-world usage.

Discussion: Do you think regulators should change testing rules or restrict PHEV credits for manufacturers — or should consumers be the ones to decide based on clearer labeling and incentives?