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DOE proposes revising procedures for calculating petroleum-equivalent fuel economy of EVs for use in CAFE calculations

The US Department of Energy (DOE) is proposing a significant revision in its procedures for calculating a value for the petroleum-equivalent fuel economy of EVs for use in the Corporate Average Fuel Economy (CAFE) program administered by the Department of Transportation (DOT). The change, petitioned for by the Natural Resources Defense Council and Sierra Club in 2021, would decrease the EV fuel economy values used in calculating CAFE compliance, thereby forcing automakers to either sell more EVs or to improve their other models to remain in regulatory compliance.

Background. In May 1980, as required by the Motor Vehicle Act, DOE proposed a method of calculating the petroleum-equivalent fuel economy of electric vehicles utilizing a “petroleum equivalency factor” (PEF). The rule was finalized in April 1981, and effective 21 May 1981. The seven-year evaluation program was completed in 1987, and the calculation of the annual petroleum equivalency factors was not extended past 1987.

DOE subsequently published a proposed rule for a permanent PEF for use in calculating petroleum-equivalent fuel economy values of EVs in February 1994 and obtained oral and written comments from interested parties. Based on the responses and other factors, DOE decided to modify the PEF calculation approach proposed in 1994; withdrew the 1994 proposed rule; and proposed a modified approach in a 14 July 1999, notice of proposed rulemaking.

DOE published a final rule on 12 June 2000. The PEF adopted by DOE in the 2000 Final Rule is based, in part, on the existing regulatory approach which provides procedures determining the petroleum-equivalent fuel economy of non-EV alternative fueled vehicles. The calculation procedure converts the measured electrical energy consumption of an electric vehicle into a raw gasoline-equivalent fuel economy value, and then divides this value by 0.15 to arrive at a final petroleum-equivalent fuel economy value which may then be included in the calculation of the manufacturer's corporate average fuel economy.

DOE has not updated this since the June 2000 Final Rule.

On 22 October 2021, DOE received a petition for rulemaking from the Natural Resources Defense Council (NRDC) and Sierra Club requesting that DOE update its regulations for calculating the PEF for electric vehicles. The petitioners asserted that the data underlying the current regulation are outdated, resulting in higher imputed values of fuel economy for electric vehicles.

The petitioners asserted that with this higher imputed value, a smaller number of EVs enable fleetwide compliance at lower real-world average fuel economy across an automaker's overall fleet.

Proposed PEF. In reviewing the PEF value, DOE must consider four factors:

  1. Energy efficiency of the electric vehicle,

  2. National average electricity generation and transmission efficiency,

  3. The need of the United States to conserve all forms of energy and the relative scarcity and value to the United States of all fuel used to generate electricity, and,

  4. Driving patterns of electric vehicles compared to those of gasoline vehicles.

DOE reviewed the methodology used to develop the current PEF value and its approach in light of these factors and concluded that some inputs should be updated to reflect more recent data, and that some components of the derived PEF value are not relevant to today's vehicles.

As a result, the proposed new PEF for the period of 2027-2031 is 23,160 Wh/gal. The current PEF is 80,049 Wh/gal. As examples of the impact:

Model Current CAFE MPGe
(PEF= 80,049 Wh/gal)
Proposed CAFE MPGe
(PEF=23,160 Wh/gal)
Volkswagen ID.4 380.6 107.4
Ford F-150 Lightning 237.1 67.1
Chrysler Pacifica PHEV 88.2 59.5

(Tesla, not surprisingly, supports granting the petition to update the PEF for electric vehicles. Tesla supports stringent CAFE standards for light-duty vehicles for efficiency gains.)

DOE will accept comments regarding this proposal on or before 12 June 2023.



The ACEEE, the American Council for an Energy Efficient Economy, an advocacy organisition, is pointing out that attention should be paid to how energy efficient electric cars are, as there is wide variance leading to very different demands for resources:

' The Environmental Protection Agency’s upcoming proposal for new greenhouse gas standards for cars and light-duty trucks starting in model year 2027 needs to address electric vehicle efficiency not only to reduce emissions, but also to lessen the impact EVs have on the electricity grid. With 300 million vehicles expected to be on the road in 2050, fully transitioning to EVs will have a significant impact on the grid. At today’s average EV efficiency of 3.4 miles per kilowatt (mi/kWh) hour,[1] 300 million EVs would add 1.2 million gigawatt-hours of electricity annually, a 31% increase from current electricity consumption.[2] That’s enough electricity to power almost 113 million homes and is consistent with other studies that show a considerable growth in electricity consumption from full or near-full electrification of light-duty vehicles. But if average efficiency was upped to the highest efficiency achieved today of 4.2 mi/kWh, full electrification of the country's light-duty vehicles would add 970,000 gigawatt-hours, 230,000 gigawatt-hours less – enough electricity to power 21 million homes U.S. homes today. '


' Model year 2023 EVs have significantly varying efficiencies, ranging from 1.9 to 4.2 mi/kWh, even among vehicles of similar weight and class. '


@Dave, absolutely.
People are driving huge EVs and giving themselves pats on the back for being green.
Also nice that they are considering the source of the electricity - Evs are not so green in West Virginia.
No-one seems to have exceeded the Tesla model 3 in terms of efficiency and (relative) affordability (OK, the Hyundai Ioniq 6 has), but the Tesla record held for quite a few years....
What we are not seeing are small, affordable efficient EVs.
The sweet spot seems to be in the middle of the range.


"The sweet spot seems to be in the middle of the range."
I suppose the problem is the weight and volume of the battery.
If you try to fit a 50 kWh battery into a Ford Fiesta, you don't have much space left, or you have to make it 80 mm taller, and there goes the aerodynamic efficiency.
Also, you have to add a considerable amount of weight for a decent battery.
So EVs don't scale down very well, unless you can tolerate quite short range.


Hi Jim

My take on aerodynamic efficiency differs a bit from consensus and practice.

That is because it is so dependent on usage.

If you are trundling up and down the motorway all the time, then it is very important.

If it is overwhelmingly a city car, mostly doing 20 or 30mph, then it is pretty irrelevant.

I have no idea how that should be weighted in efficiency ratings, but I suspect that smallish BEVs with 50KWh batteries or so are not going to spend much of their time going fast.

The bottom line is that for me the ideal city BEV is something along the lines of the original Citroen 2CV, which legend has it was designed so that a French farmer could drive it without removing his high hat over ploughed fields!;-0

Light is important for city cars, aerogoddamits no so much.....


This is a bad idea because it is energy grid BACKWARD looking and vehicles average life is 17 years and the grid will have vastly lower carbon emissions every decade moving forward.


Hi GdB

I'm not sure I follow you.

' The change, petitioned for by the Natural Resources Defense Council and Sierra Club in 2021, would decrease the EV fuel economy values used in calculating CAFE compliance, thereby forcing automakers to either sell more EVs or to improve their other models to remain in regulatory compliance. '

I don't see how that is hurt by the grid becoming less carbon intensive?

Probably me being dim, but perhaps you could explain your thinking in a bit more detail?



Take natural gas burn it in a power plant charge an electric car,
take the same amount of natural gas put it in an engine not much difference.



OK you are correct on that point but consider that with a future 100% clean grid and decarbonized heavy industry, (fast approaching in some states), MPGe is irreverent, with zero emissions.

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