Transport & Environment (T&E) bases its analysis on data from the European Environment Agency. According to this, real-world CO2 emissions from plug-in hybrids registered in 2024 were, on average, around six times higher than official figures. In 2023, T&E reported that this factor was still around five.
For drivers, this discrepancy also has financial consequences. T&E estimates that the additional fuel costs, compared to official consumption figures, for a PHEV sold in 2024 amount to an average of 680 euros per year. Even compared to conventional internal combustion engine vehicles and non-plug-in hybrids, the real-world advantage is smaller than the official figures suggest. According to T&E’s analysis, actual emissions from plug-in hybrids were only 14 percent lower than those from these vehicles. By contrast, official test values suggested an 83 percent reduction.
According to T&E, one of the reasons is that the internal combustion engine also runs regularly during supposedly electric operation. The analysis found this to be the case for about a third of the kilometers driven in battery mode.
The gap between testbed and real-world conditions is not a new problem, as the International Council on Clean Transportation (ICCT) demonstrated this summer. In an evaluation of around eight million vehicles, researchers found that in 2023, real-world PHEV emissions were, on average, about five times higher than official test values. The ICCT cited causes such as lower-than-anticipated electric driving performance, frequent use of the internal combustion engine, and the additional weight of the dual propulsion system.
Disputing the ‘utility factor’ in CO2 reduction
At the center of the current regulations is the so-called utility factor. This determines what proportion of a plug-in hybrid’s mileage is assumed to be electric when calculating official CO2 emissions. The EU has already adjusted this factor to bring approval values closer to real-world use.
The car industry is also exploring how to technically impose a greater proportion of electric driving. In 2025, the VDA proposed designing future plug-in hybrids that must be charged periodically. If charging does not occur within a yet-to-be-defined driving distance, powertrain power could be reduced. The proposal aimed to address criticism that it has so far been difficult to ensure the proportion of electric driving of PHEVs in the real world.
T&E already sees a technical effect in the first correction. The organization analyzed 20 of the best-selling PHEV models, which together accounted for 51 percent of sales in 2025. According to the analysis, manufacturers responded, among other things, with larger batteries and longer electric ranges.
According to T&E, the adjustment was especially pronounced in Volkswagen Group models. For the VW Tiguan, the electric range increased from 55 to 119 km. As a result, official emissions remained at 36g CO2/km despite stricter calculations, compared to 32g/km previously. In five VW models examined, around 90 percent of the increase in official emissions caused by the utility factor correction was compensated in this way.
According to T&E’s assessment, manufacturers could also absorb the upcoming adjustment through new technical improvements. For example, increasing electric range, improving the efficiency of internal combustion engines, reducing weight, improving aerodynamics and optimizing recovery. The organization believes it is possible to keep PHEVs below the 50g CO2/km threshold.
However, the upcoming fix is politically controversial. T&E warns against freezing the profit factor at the 2025/26 level. According to the organization’s calculations, real-world PHEV emissions would still be underestimated by 56 percent.
This would not only affect the consumption figures provided to customers. The estimated low PHEV emissions also affect the CO2 balance of the manufacturers’ fleet and may therefore influence the number of pure electric cars that must be sold to meet European fleet targets.
The ICCT had already noted that the latest correction is insufficient to fully reflect real-world PHEV emissions. Therefore, both analyzes reach a similar conclusion despite the different databases. After all, the climate balance of plug-in hybrids depends not only on their technical design but, above all, on the frequency with which they are driven and electrically charged.
transportenvironment.org
