Not as restricted by charging infrastructure as electric vehicles, and less environmentally burdensome than gasoline cars—such has been the appeal of plug-in hybrid vehicles, or PHEVs, which have been gaining popularity as cars that combine the best of both worlds. However, these vehicles are now facing renewed scrutiny.

According to the latest analysis of approximately 920,000 PHEVs operating in Europe, the amount of carbon dioxide emitted on the road significantly exceeded the figures indicated in catalogs and type approvals. The issue is compounded by the fact that this gap is widening with newer vehicles.

For PHEVs registered in 2021, the actual CO₂ emissions were about 3.5 times the nominal values. By 2023, this discrepancy had grown to approximately 4.6 times.

At first glance, these results seem puzzling. Recent PHEVs have larger battery capacities and longer electric-only driving ranges. If technology is advancing, one would expect actual CO₂ emissions to decrease.

However, this is not necessarily the case on real roads.

What exactly is a PHEV?

In broad terms, a PHEV is a "chargeable hybrid vehicle."

Like conventional hybrid vehicles, they are equipped with internal combustion engines such as gasoline engines and electric motors, but they differ significantly in that they can be directly charged from household power sources or charging facilities.

For short commutes or shopping trips, they can run on electricity alone, while for long-distance travel, the engine is used. For users in areas with few charging facilities or those who frequently drive long distances, PHEVs offer more reassurance than fully electric vehicles.

If operated ideally, they can cover most daily driving on electricity, using the engine only when necessary, such as for travel.

There is nothing inherently wrong with this concept.

The problem lies in "how much they actually run on electricity."

Assumed "about 80% electric driving," reality is about 20%

A key focus of this analysis is the significant gap between the assumed proportion of electric driving under regulatory frameworks and the actual usage.

When calculating the official CO₂ emissions of PHEVs, it is necessary to assume how much the vehicle will run in electric mode.

In European certification systems, assumptions are made based on factors such as battery range, reflecting these assumptions in the CO₂ emissions calculations.

According to the ICCT analysis, assuming an electric driving ratio of about 21% in 2022, which is closer to reality, aligns better with actual driving, whereas the official calculation assumed a very high ratio of about 80%.

In other words, while the calculations treat the vehicle as if it runs mostly on electricity, in reality, electric driving may not be used as frequently.

This discrepancy leads to a significant divergence between the nominal CO₂ and actual CO₂ emissions.

Despite longer electric ranges, the proportion of electric driving decreases

Another intriguing point from this study is that improvements in battery performance do not necessarily lead to better environmental performance.

Normally, if the electric-only driving range extends from 30 km to 50 km, and further to 80 km, one would expect an increase in the distance covered without using the engine.

The official calculation methods are generally based on this assumption.

However, real-world driving data shows that while the electric range of PHEVs increased from 2021 to 2023, the actual proportion of driving done on electricity decreased.

According to the ICCT, the average actual CO₂ emissions increased from about 130 grams per kilometer in 2021 to about 134 grams in 2023.

Meanwhile, the official figures decreased from about 37 grams to about 29 grams.

Thus, while catalog figures suggest improved environmental performance, on the road, there is little improvement, and the trend is towards deterioration.

This combination of factors has rapidly widened the gap between nominal and actual figures from 3.5 times to 4.6 times.

"Chargeable cars" vs. "actually charged cars"

When considering PHEVs, it is crucial to understand that environmental performance cannot be judged solely by the vehicle's capabilities.

For instance, users who charge their vehicles at home every night and whose daily commute falls within the electric range can live almost without using the engine.

Conversely, if a user owns a PHEV without home charging facilities and rarely charges it elsewhere, the vehicle, equipped with a large battery and motor, will primarily run on the engine.

PHEVs carry both an engine, fuel tank, motor, and a large-capacity battery, which generally increases vehicle weight.

Driving primarily with the engine without charging can result in carrying "equipment installed for electrification" as dead weight.

The ICCT points out that not only low charging frequency but also scenarios where the engine and motor operate simultaneously, and the increased weight from having two powertrains, contribute to higher energy consumption.

Analyses indicate that the actual CO₂ emissions of PHEVs during real-world driving were only about 18% lower on average than those of internal combustion engine vehicles or conventional hybrids.

It is not a given that "because they are electric vehicles, they automatically result in significantly lower emissions."

Analysis of the "actual usage" of 920,000 vehicles

One reason this result is noteworthy is that it is based on large-scale real-world driving data, not just laboratory tests.

The study examined approximately 920,000 PHEVs registered in Europe between 2021 and 2023.

In Europe, data on actual fuel and energy usage is collected using onboard fuel and energy consumption monitoring systems installed in new cars.

This allows for observing real usage trends, including daily commutes, shopping, highways, and long-distance travel, beyond just test courses set under specific conditions.

Of course, not all 920,000 vehicles operate under the same conditions. However, aggregating such a large number of vehicles provides crucial insights into how PHEVs are used across society.

Is the problem solely with the users?

It's easy to blame "drivers who don't charge," but the reality may be more complex, with systems and corporate structures potentially influencing charging behavior.

PHEVs are often used as company cars or corporate fleets in Europe, and discussions on related social media frequently highlight cases where fuel cards are provided by companies, covering gasoline costs, while home charging costs fall on employees.

In such situations, it becomes more rational for drivers to refuel with company-covered gasoline rather than paying out of pocket for charging.

Similar issues exist with rental cars.

Travelers renting PHEVs may not always seek out charging spots, pay fees, and wait for charging just to gain a few dozen kilometers of electric range.

As a result, PHEVs, designed to be frequently charged, may end up being used as "heavy hybrids that are hardly ever charged."

This is a problem that cannot be solved by vehicle technology alone.

On social media, "PHEV unnecessary" vs. "depends on usage"

The topic of PHEV's real-world emissions has long sparked significant debate on social media and online communities.

In automotive and EV-related communities abroad, discussions around the same ICCT data have led to criticisms such as "many corporate vehicles are introduced to benefit from tax incentives for PHEVs but are not actually charged" and "without mechanisms to encourage charging, incentives for PHEVs are meaningless."

Some even argue strongly that "incentives for PHEVs should be reduced and redirected to fully support EVs."

On the other hand, there are also many rebuttals against dismissing PHEVs entirely.

Actual owners have shared experiences like "I charge at home every night and can mostly drive on electricity in daily life" and "I only use the gasoline engine for long-distance travel, which suits my usage perfectly."

Additionally, some point out that in cold winter environments or during long-distance travel, engine usage rates increase, making it insufficient to judge solely by the number of charges.

Organizing the reactions on social media reveals that the issue is not a binary choice of whether PHEV technology is good or bad.

The key point, on which both proponents and critics surprisingly agree, is that the conditions of use—"who charges, in what environment, and how frequently"—are crucial.

It is important to view these social media posts not as representative of overall public opinion but as indicative of key discussion points visible in publicly available threads.

Official CO₂ values also affect manufacturers' regulatory compliance

This issue is not merely about the difference between catalog fuel efficiency and actual fuel efficiency; it is also related to automakers' CO₂ regulations.

In the EU, targets are set for the CO₂ emissions of all new cars sold by manufacturers.

If PHEVs are assigned very low official CO₂ values, selling many of them can lower the overall average for the manufacturer.

However, if these PHEVs emit far more CO₂ on the road than their nominal values suggest, a situation arises where "regulatory compliance appears to contribute to emission reductions, but in reality, it does not reduce as much."

The ICCT points out the possibility that PHEVs could be excessively favored in regulations compared to conventional engine vehicles.

The EU is already aware of this issue and is working to revise the "utility factor" used in PHEV CO₂ calculations.

The first phase of revisions will begin in 2025, with stricter adjustments scheduled to apply from November 2026, known as the 2027 phase.

This change aims to align official CO₂ emissions more closely with real-world usage.

Will the PHEV market disappear?

That doesn't necessarily mean PHEVs will disappear from the market immediately.

In the first half of 2026, while battery EVs accounted for over 20% of the EU new car market, PHEVs maintained about a 10% market share.

For consumers hesitant about transitioning to fully electric vehicles, PHEVs remain an attractive option.

Especially for those who can charge at home but occasionally travel long distances, frequently drive in areas with insufficient charging infrastructure, or still have reservations about fully transitioning to EVs, the use of "EV for daily life, gasoline for long distances" is rational.

However, if future official CO₂ calculation methods become more aligned with reality, the regulatory benefits of selling PHEVs for manufacturers may diminish.

In that case, automakers might further shift towards increasing the sales ratio of fully battery EVs rather than expanding PHEV offerings.

PHEVs have been valued as "bridges to EVs."

Going forward, it will be necessary to prove with real-world driving data whether this bridge truly leads to CO₂ reduction.

The real issue lies in "assumptions" rather than "technology"

The most important point highlighted by this study is not that PHEVs themselves cannot be established as environmental technology.

The problem is the significant gap between the assumption that "if the battery range is long, users will drive more on electricity" and actual usage behavior.

People who can charge daily at home or work can fully utilize the environmental performance of PHEVs.

However, the situation differs for those without charging facilities, corporate car users who bear charging costs themselves, those mainly using the vehicle for long distances, or rental car users.

Even the same model can have vastly different CO₂ emissions depending on usage.

Therefore, in the future, the focus should be not only on "how far a car can theoretically run on electricity" but also on "how much it is actually driven electrically in society."

The real-world data from 920,000 vehicles highlights the reality that the name "eco-car" alone cannot determine environmental performance.

In the automotive market, where electrification is becoming mainstream, the question is not about the numbers on a spec sheet.

It is about whether the technology is truly integrated into real-life usage.

Source

BUSINESS Panorama

An AFP article reports that the actual CO₂ emissions of PHEVs during real-world driving were about 3.5 times the nominal values for 2021 registered vehicles and expanded to about 4.6 times for 2023 registered vehicles, based on an analysis of data from approximately 920,000 vehicles. URL:

https://business-panorama.de/news.php?newsid=6710030

International Council on Clean Transportation (ICCT) Press Release

The official announcement of the study released in September 2026. It explains the real-world driving data of approximately 920,000 PHEVs, the gap with nominal CO₂ values, the electric driving ratio, and the EU's 2027 system revision. URL:

https://theicct.org/pr-plug-in-hybrid-emissions-gap-widens-despite-longer-electric-ranges-icct-study-shows/

ICCT Working Paper "Fair game: Restoring technology neutrality through plug-in hybrid utility factor adjustment"

Detailed documentation of the study covered in this article. It analyzes onboard fuel and energy consumption data