Some automakers aim to use plug-in hybrids as a bridge to all-electric cars, but tougher European regulations might put an end to that sooner than expected, according to a Reuters report.

Draft regulations would prevent automakers from labeling plug-in hybrids as "sustainable investments" beyond 2025, potentially discouraging investors, while stricter emissions rules could force automakers to transition to all-electric cars earlier, according to the report.

It's worth noting that variation in timing appears to only be a few years. The CEOs of Bentley and Volvo told Reuters that European regulators were moving to phase out plug-in hybrids too quickly, but also noted that they are aiming to make their brands' lineups all-electric by 2030.

Plug-in hybrids initially seemed like a reasonable compromise before substantial public infrastructure was built up, when many drivers were unfamiliar with EVs and more susceptible to range anxiety. But now many Europe countries have large networks of charging stations, and research indicates plug-in hybrids may not be as green as originally thought.

Some real-world tests have suggested they’re polluting much more than claimed, possibly more than non-hybrids in some cases where they’re not regularly charged, or when charge-restoring modes are used. And some plug-in hybrids—from luxury brands especially—have has embarrassingly short electric ranges.

2021 Bentley Bentayga Hybrid

2021 Bentley Bentayga Hybrid

That’s far from the intent of the Chevrolet Volt, which ushered in plug-in hybrids as a viable possibility—and quicker path toward more EVs, potentially, a decade ago.

However, by giving owners the option to drive without charging, plug-in hybrids have never offered as definite an environmental benefit as all-electric cars. Even General Motors has phased out the Volt in favor of the Chevy Bolt EV and other planned all-electric models.

Whether to include plug-in hybrids in an emissions-reduction strategy is more a matter of anticipated consumer behavior than overall environmental impact. Studies have hinted at a ceiling for EV growth in Europe, which outperformed expectations last year. The concern, however, is that Europe is moving at two speeds on EV adoption, with robust sales of fully electric vehicles in wealthy countries, and fewer sales in poorer countries.

Which leads to a question: Will the United States take the lead from Europe with its own EV policy, seeing plug-in hybrids as a transitional technology? Or will it leave that up to automakers?