Plug-In Hybrid Real-World Emissions Reveal Steep Fuel Cost Gaps
Plug-in hybrid electric vehicles emit an average of 146 grams of CO2 per kilometer in everyday driving, missing official laboratory homologation promises by a wide margin, according to transport and environment data detailed by automotive publication Gocar.be. While official ratings suggest these vehicles produce just 24 g/km—representing an 83% reduction compared to standard combustion engines—actual measurements show a reduction of barely 14% over standard petrol, diesel, and traditional hybrid models.
The European Environment Agency collected the data for the study titled ‘Still smoking,’ which analyzed real-world fuel consumption for vehicles registered in 2024. The findings highlight a deep chasm between official laboratory testing and how motorists actually operate dual-fuel vehicles on public roads.
Regulatory Changes and Discrepancies in Fuel Consumption Calculations
Official emissions figures rely on a utility factor that estimates the proportion of kilometers driven on battery power alone. Regulators are adjusting these formulas because drivers charge their batteries far less frequently than laboratory models assume. For example, vehicles with a 100-kilometer electric range were previously calculated at 90% electric operation, a figure that dropped to roughly two-thirds and is scheduled to fall to 44% by November 29, 2026.
Transport & Environment calculates that plug-in hybrids cover only 40% of their distance using the battery, with just 27% driven in pure electric mode. Even when fully charged, the combustion engine engages during roughly one-third of a standard trip. Under older calculation methods, real-world emissions ran 6.1 times higher than official ratings, a ratio that drops to 2.3 under current rules and is projected to hit 1.5 for newly homologated models by November 27, 2026.
Automakers responded to initial rule changes by installing larger battery packs, such as the Volkswagen Tiguan PHEV increasing its electric range from 55 to 119 kilometers while maintaining an official rating of 36 g/km. However, larger hardware yields minimal environmental benefit if owners fail to plug the vehicle in regularly.
Financial Impact on Vehicle Owners
Electric driving generally costs less than running on petrol, but frequent reliance on the combustion engine drives up expenses at the fuel pump. Transport & Environment estimates that the average owner of a plug-in hybrid sold in 2024 spends 680 euros more annually on fuel than official homologation figures suggest. Even when factoring in current calculation methods, the annual shortfall remains 515 euros. These figures assume an annual distance of 12,730 kilometers and incorporate energy prices recorded following the conflict in Iran.
Franco-German Agreement and Proposed Charging Mandates
A recent Franco-German agreement aimed at softening the transition to full electrification proposes freezing the utility factor until January 1, 2030, for plug-in hybrids offering a minimum electric range of 80 kilometers. Policymakers also weighed a proposal to mandate regular charging, potentially requiring drivers to plug in at least once every 750 kilometers. Vehicles failing to meet this threshold would face automated electronic limitations on motor power.
Critics note that a 750-kilometer interval with an 80-kilometer or 100-kilometer electric range requires an electric driving share of roughly 10% to 13%, well below the 27% pure electric usage already documented by environmental monitors.
Declining Market Share Across Belgian Showrooms
The Belgian new car market shows a sharp contraction in plug-in hybrid sales following the tightening of fiscal deductibility rules at the end of 2023. These models accounted for 21.1% of all new vehicle registrations in 2023, but that share dropped to 14.9% in 2024, 9.3% in 2025, and down to 5.6% in the first half of 2026.
Absolute sales volumes fell from 66,640 new units in 2024 to 38,755 units in 2025, marking a 41.8% decline in a single year. Sector federation Traxio reports an opposite trend on the secondhand market, where the combined market share of traditional hybrids and plug-in hybrids rose from 10.6% in 2024 to 15.2% in the first half of 2026, though federation statistics do not separate the two powertrain types.
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