One major issue with how the EPA conducts its fuel economy testing is that the tests are conducted in a way that doesn't imitate real-world driving. Vehicles are run on a dyno at a certain speed for a specific amount of time and viola, you get official EPA fuel economy figures. To match the EPA’s fuel economy figures for plug-in hybrid vehicles (PHEV), the cars have to be fully topped up on both electricity, but that’s not happening in the real world, which could translate to worse fuel economy for owners and higher emissions.
According to a new study from the International Council on Clean Transportation (ICCT) that Green Car Reports found, the number of miles that PHEV travel solely on electricity may be down 25%-65% compared to figures regulators assumed they would be. This results in fuel economy that’s 42%-67% higher than official EPA figures found on a vehicle window sticker. The study came to these figures based on self-reported fuel economy figures from Fuelly.com and data for engine-off miles traveled by the California Bureau of Automotive Repair (BAR).
To get the best fuel economy from their PHEVs, owners should be charging their vehicles as frequently as possible to keep the battery pack topped up. But unlike all-electric vehicles where charging is mandatory, it isn’t with PHEVs. Since PHEVs can run on gasoline, drivers don’t have to charge as regularly as they have to with a pure EV. While driving on gasoline is more convenient for owners, it’s not as efficient. There’s no main explanation for why PHEV owners are choosing not to charge their vehicles, but a lack of available chargers could be one explanation.
The ICCT has a few recommendations on how the EPA can obtain real-world fuel economy figures for PHEVs. The organization believes that regulators should be looking at the actual number of miles PHEV owners drive in all-electric mode. The EPA can apparently do this by gathering data “through on-board diagnostic reporting requirements.”
Additionally, the organization recommends setting minimum electric range requirements for PHEVs. As Green Car Reports points out, California has range requirements for zero-emissions vehicle credits under its Advanced Clean Cars II standard. In the future, California will require PHEVs to have a range of 50 miles based on specific test cycles, like a momentary top speed of 80 mph and several bursts of acceleration. At the moment, the Toyota RAV4 Prime has one of the longest ranges of any PHEV on the market with an all-electric range of 42 miles.
Analysts have a few suggestions that would make PHEVs more like EVs to help require owners to charge their vehicles more. Some of the suggestions include having a maximum gas tank size, requiring PHEVs to come with fast-charging capability, and having a minimum amount of power that comes from the all-electric portion of the powertrain.
While most consumers would prefer to purchase a PHEV over a pure EV, studies like this one show that they’re not necessarily the most efficient options on the market. In 2020, a report from the environmental group called Transport & Environment found that the real-world emissions from PHEVs in Europe were much higher than their official ratings, claims Green Car Reports.
Source: Green Car Reports
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