New Study Says Plug-In Hybrids Are Almost As Dirty As Gas Cars

Plug-in hybrid electric vehicles (PHEVs) have long been promoted as a cleaner stepping stone toward full electric mobility. But a new study by Transport and Environment (T&E), “Europe’s leading advocates for clean transport and energy” suggests that reality doesn’t live up to the promise. According to T&E’s latest report, PHEVs are “nearly as dirty as gas cars”, emitting far more carbon dioxide (CO?) in real-world driving than official lab tests claim.

The findings cast serious doubt on the role of plug-in hybrids as a meaningful bridge to electric vehicle (EV) adoption and may reshape how policymakers and consumers view their environmental impact.

T&E’s analysis, based on data from the European Environment Agency (EEA), examined emissions readings from 127,000 plug-in hybrids registered in 2023 across the European Union. The results were eye-opening: “In the real world, plug-in hybrids emit 135g of CO? per kilometer on average,” T&E reported, “compared with 166g/km for petrol and diesel cars.”

That means PHEVs are producing just 19% fewer emissions than conventional vehicles not the 75% reduction originally indicated by laboratory testing. In other words, PHEVs are performing nearly five times worse in everyday conditions than automakers claim.

So, why do plug-in hybrids emit so much more CO? in practice? The study identifies several key reasons:

Many PHEVs designed for both European and U.S. markets are heavier than conventional cars due to their larger batteries. Ironically, the models with the longest electric-only ranges (over 75 km) were found to produce more CO? emissions than shorter-range models.

T&E explained: “PHEV emissions are also increasing because of the trend towards longer electric ranges as bigger batteries make the vehicles heavier and, therefore, burn more fuel in engine mode. These heavier vehicles also consume more energy than smaller cars when driven on the battery.”

The added weight means that once the electric charge is depleted or even during hybrid operation the gas engine must work harder, burning more fuel to compensate.

Another uncertainty lies in how often owners actually plug in their vehicles. A PHEV’s environmental advantage hinges on regular charging, but T&E notes that many drivers rely heavily on the gasoline engine, either out of convenience or lack of access to charging infrastructure.

This behavioral gap effectively turns many PHEVs into standard hybrid or gas cars, negating their theoretical emissions benefit.

The study also points out that most PHEV electric motors can’t handle all driving conditions particularly at high speeds or on steep inclines. In those scenarios, the gas engine kicks in, even when the car is supposedly in electric-only mode.

As a result, the vehicles can burn up to 3 liters of fuel per 100 kilometers (0.8 gallons per 62 miles), generating 68g of CO? per kilometer about 8.5 times higher than the official emissions predicted for electric operation.

This mismatch between lab testing and real-world conditions exposes a structural flaw in how PHEV performance is evaluated.