- Plug-in hybrids emit nearly five times more CO2 than officially claimed.
- T&E tested 800,000 cars and found emissions figures highly inaccurate.
- Many owners rarely charge their plug-ins, relying on gasoline instead.
The green halo around plug-in hybrid vehicles is starting to crack, and a new study from Transport & Environment (T&E) has turned up the pressure. What was once seen as the ideal bridge between combustion and full electrification now appears less virtuous under real-world scrutiny.
According to the organization’s testing of 800,000 cars, PHEVs in everyday European use are pumping out nearly five times more CO2 than the official test figures suggest.
The Everyday Reality
For years PHEVs have been promoted as the perfect compromise between fully electric vehicles and traditional petrol cars. You plug in when you can, drive in electric mode for short trips and rely on petrol when longer excursions call.
Newer PHEVs can travel more than twice as far on electric power as older ones – up to 70 claimed miles (113 km), in some cases – and they may even be allowed to live on after Europe’s 2035 combustion ban has come into force.
But in the real world, many owners forget or don’t bother to plug them in and instead drive them mostly on petrol. And even when charged, the study found that PHEVs quickly switched to their combustion engines under moderate acceleration, on hills, or in colder weather.
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That meant their electric systems were doing less of the heavy lifting than regulators assumed when certifying them.
Numbers That Don’t Add Up
That gap, it turns out, is only widening. Back in 2021, T&E recorded real-world emissions of 134 g/km for plug-in hybrids, roughly 3.5 times higher than the official 38 g/km figure. In its latest study, the difference has ballooned: manufacturers now claim an average of 28 g/km, yet testing shows a far heavier 139 g/km.
For consumers who bought a PHEV on the promise of low emissions and lower running costs the reality may be higher fuel bills and a larger carbon footprint.
T&E suggested to The Guardian that families might be paying €500 ($580/£435) more per years than they would if their car achieved the mpg numbers claimed. And for governments and regulators relying on PHEVs to hit fleet emissions targets the risk is that the tool is far less effective than assumed.
According to T&E, carmakers may have sidestepped billions in potential fines by leaning on optimistic PHEV emissions accounting.
Lawmakers have been made aware of this situation through previous studies and are phasing in tougher rules that reduce the “utility factor,” the time a PHEV is presumed to spend in EV mode, when calculating CO2 figures.
Under current rules, a PHEV with a 60 km (37 miles) range is expected to drive in electric mode over 80 percent of the time, though that drops to 54 percent for 2025/26 and 34 percent for 2027/28.
But T&E says there would still be an 18 percent gap between claimed and achieved CO2 output even after applying the ’27/28 framework.
