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Is the EPA Overstating the Mileage of Plug-In Hybrid Electric Vehicles?

The purpose of this article is to provide some clarification, as there appears to be some confusion regarding the EPA MPG equivalents for plug-in hybrids and EVs. People, especially energy systems analysts, find it not credible to have a Chevy Volt achieve 37 EPA Combined in hybrid mode, but, according to the EPA, achieves an MPG-e of 98 MPG-e in EV mode.


Below are two methods to calculate the MPGs and CO2 emissions, grams per km, of plug-in hybrids and EVs. 


Method No. 1 is based on the energy input to the US power system in EV mode, and the energy of gasoline in hybrid mode.


Method No. 2 is based on an EPA method which results in EPA-invented “MPG equivalent” values, as determined by EPA standard tests that simulate different driving conditions.


Note: The US is the only major vehicle-producing nation using this method. If other nations sell imported vehicles in the US, their mileage labels must be in the EPA-mandated format.


Also provided is a description of the European approach, which is based on Method No. 1. 




In the below referenced article is was concluded: 


– replacing coal plants by up to 60% efficient, gas-fired CCGT plants would be the fastest, lowest-cost approach to significantly reduce CO2 emissions. It would have minimal need for electric grid modifications and, because of abundant, domestic, low-cost, low-CO2 mitting, gas, almost no effect on household and business electric rates.


– replacing low-mileage, light-duty vehicles with high-mileage vehicles would be a much less costly approach to moderately reduce CO2 emissions than replacing them with plug-in hybrids and all-electric vehicles. 


– A Chevy Volt in EV mode (energy from the US grid) has the same CO2 emissions, g/mile, as a 100% gas vehicle with an EPA Combined of 50 MPG.


This article concludes the EPA approach of using “MPG-equivalent” as a metric for guiding consumer purchases of light-duty vehicles is technically invalid, deceptive and confusing. It is out of step with other vehicle manufaturing nations, such as Europe, China and Japan, which use grams of CO2 per kilometer or per mile as metrics.


As the US, Europe, China and Japan manufacture most of the world’s light-duty vehicles and export to each other, it is essential to have an easy-to-understand, global CO2 emissions standard in grams per kilometer or per mile that promotes the end result, which is less CO2 emissions from tailpipes and chinmeys. 




The US has 3 grids that are interconnected: the Eastern and Western Interconnection and the Texas grid; all are in sync at 60 Hz. The US grid CO2 intensity varies very little from year to year. It will be slowly decreasing, as more CO2-free energy is added over the years. 


Energy travels on the grid as electromagnetic waves at nearly the speed of light, 1800 miles in 0.01 second, and the energy travels not through the copper wires, but in the air adjacent to the copper wires, and the copper surface electrons vibrate in place at 60 Hz. 


Energy, as electromagnetic waves, continuously fills in many millions of voltage “valleys” created by various demands. No energy fed into the grid from thousands of sources is “local”. That means the grid energy of the Midwest, East Coast and West Coast, etc., is the same.


As Chevy Volts will be driven all over the US, the CO2 emission, gram/mile, can be calculated by using the US grid CO2 intensity, lb CO2/kWh, as the calculation basis. 


CO2 Emissions: Upstream and Plant Self-Use and Grid Losses: For any proper comparison regarding CO2 emissions of high mileage vehicles vs plug-in hybrids and all-electric vehicles, the CO2 emissions of extracting, processing and transporting the fuel to the user, as well as the power plant self-use and grid losses should be counted.


Coal and Gas: CO2 emissions for extraction, processing, and transporting coal and gas to power plants are about 4.4% and 23.4%, respectively, a weighted average of 8.36%. See cleanskies URL, page 10 


Fuel Oil and Other: CO2 emissions for extracting, transporting to refinery, refining, and distribution to gas pumps are as shown below. Refining CO2 emissions are 2.5 lb CO2/gal. See cleanskies URL.


CO2 Emissions from well to pump: 

                                                               lb CO2/gal

Exploration/Production, 8%                         2.00   

Transport, 1%                                            0.25  

Refining, 10%                                             2.50

Distribution, 1%                                          0.25   

Total                                                          5.00 


CO2 adjustment factor for Fuel Oil and Other: (19.4 + 5)/19.4 lb CO2/gal = 1.2577

See accenture URL, page 3.


                                                                                    Btu           kWh         kWh/mile

Energy extracted                                                       424,740      124.47      1.2928

Extraction, processing, transportation losses, 8.36%      35,502 

Fuel energy to plant                                                   389,238      114.06      1.1847

Conversion loss, 67%                                                 259,492 

Electrical energy produced, 33%                                 129,746       38.02       0.3949

Plant self use, 5% of production                                      6,487 

Electrical energy to grid                                              123,259       36.12       0.3752                     

US grid T&D losses, 6.7% of grid feed in                          8,258 

Energy to vehicle, at user’s meter                               115,000       33.70       0.3500     


– Primary energy of 424,740 Btu, equivalent to about 3.63 gallons of gasoline, is required to deliver 33.7 kWh (same Btu as 1 gallon of gas) to the user’s meter. 

– The 33.70 is the kWh equivalent of one gallon of gas.

– The 0.3500 is the kWh/mile, as measured at the user’s meter, per EPA.




In May 2012, the US finalized new standards to increase the corporate average fuel economy, CAFE, of light-duty vehicles (cars, SUVs, minivans, and 1/4-ton trucks) from the current 27.5 MPG, to 35.5 MPG by 2016, to 54.5 MPG by 2025.


Below is a comparison of 2 cases of travel. See URL.


                                      Travel          Mileage        Energy               Emissions  

                                                            MPG                           lb CO2/yr   g CO2/km                 


Present CAFE                    12,000          27.5          436 gal       10,647      250.36          

2025 CAFE                       12,000          54.5          220 gal         5,372      126.33


Below are the calculations for each of the values in the above table.


454 g = lb; 1 m = 1.609 km

Travel = 12,000 miles/yr


Present CAFE 

Energy = 12,000 m/yr x 1 gal/27.5 m = 436 gal/yr 


CO2 emission = 436 gal/yr x 24.4 lb CO2/gal = 10,647 lb/yr 


CO2 emission = 24.4 lb CO2/gal x 1 gal/27.5 m x 454 g/lb x 1 m/1.609 km = 250.36 g/km 


2025 CAFE

Energy = 12,000 m/yr x 1 gal/54.5 m = 220 gal/yr 


CO2 emission = 220 gal/yr x 24.4 lb CO2/gal = 5,372 lb/yr


CO2 emission = 24.4 lb CO2/gal  x 1 gal/54.5 m x 454 g/lb x 1 m/1.609 km = 126.33 g/km


Below are additional calculations of CO2 emissions, g/km.


Chevy Volt, EV mode: 35 kWh/100 m, as measured at user’s meter, or 38.78 kWh/100 m, as produced by power plant. CO2 emissions/m = 0.3878 kWh/m x 1.154 lb CO2/kWh, US grid CO2 intensity x 1.0836, upstream factor = 0.4848 lb/m, or 0.4848 lb/m x 1 m/1.609 km x 454 g/lb = 136.8 g/km, referred to coal mine and gas well.


Chevy Volt, hybrid mode, (combined city/highway, not counting any EV miles): When the battery is depleted, the car operates as a standard hybrid and consumes 6.36 l/100 km (EPA Combined 37 MPG) with CO2 emissions of 19.4 lb CO2/gal x 1 gal/37 m x 1 m/1.609 km x 454 g/lb = 147.9 g/km, as measured at the tailpipe, or 147.9 x 1.2577 = 186.1 g/km, referred to the oil well.


For comparison:

Toyota plug-in hybrid, EV mode: 32.2 kWh/100 m, as measured at user’s meter, or 35.68 kWh/100 m, as produced by power plant. CO2 emissions/m = 0.3568 kWh/m x 1.154 lb CO2/kWh, US grid CO2 intensity x 1.0836, upstream factor = 0.4461 lb/m, or 0.4461 lb/m x 1 m/1.609 km x 454 g/lb = 125.9 g/km, referred to coal mine and gas well.


Toyota plug-in hybrid, hybrid mode, (combined city/highway, i.e., not counting any EV miles): When the battery is depleted, the car operates as a standard hybrid and consumes 4.7 l/100 km (EPA Combined 50 MPG) with CO2 emissions of 19.4 lb CO2/gal x 1 gal/50 m x 1 m/1.609 km x 454 g/lb = 109.5 g/km, as measured at the tail pipe, or 109.5 x 1.2577 = 137.7 g/km, referred to the oil well.


                                       Energy            Energy      Energy by Plant           CO2 Emission

                                 kWh/100 m         l/100 km       kWh/100 m               g/km      g/km

Chevy Volt, EV                 35.0                                     38.78                                 136.8+

Chevy Volt, hybrid                                   6.36                                          147.9*    186.1**

Toyota Prius, EV               32.1                                      35.68                                125.9+

Toyota Prius, hybrid                                 4.70                                          109.5*    137.7**


*Tail pipie

+Coal mine, gas well

** Oil well


Gas Mileage and Curb Weights: As curb weight decreases, gas mileage increases exponentially, according to the equation: mileage = a x curb weight to the power b + c.  


Using the equation, the calculated Toyota Prius EPA combined MPG = (3,781 squared/3,042 squared) x 37 MPG Chevy Volt = 57 MPG; the actual is 50 MPG. Eventhough the Chevy Volt is heavy, it still gets good mileage in hybrid mode, compared to a Toyota Prius. 



The energy consumption of a vehicle is determined by the EPA’s five standard drive cycle tests simulating varying driving conditions. All new cars and light-duty trucks sold in the U.S. are required to have a label showing the EPA’s estimate of fuel economy of the vehicle. 


The “MPG equivalent” metric for plug-in hybrids and EVs, introduced in November 2010 by the EPA, is based on equating 33.7 kWh of electrical energy with the thermal energy of one gallon of gasoline. The method produces high MPG-e values for plug-in hybrids.


Per EPA, Chevy Volt in EV mode = 100 m/35 kWh x 33.7 kWh/gal = 96.3 MPG-e. (the below website states 98 MPG-e.)


Per EPA, Chevy Volt in hybrid mode: City 35, Highway 40, Combined 37 MPG; based on 45% highway, 55% city driving, and 15,000 annual miles.


EPA’s Political MPG-e Creation: The EPA MPG-e is an artificial creation which is not used by any other nation in the world. It has no physical reality regarding actual energy consumption/mile and CO2 emissions/mile, because it erroneously equates the thermal energy in a gallon of gas with 33.7 kWh of electrical energy.


But, the EPA method does serve a political purpose, as it allows manufacturers to use the high MPG-e values for calculating their CAFE values, which would make it much easier to comply with the 2025 CAFE standard.



The federal government is providing a subsidy of $7,500 per Chevy Volt to achieve a CO2 emission reduction of a few gram/km. 


Instead of spending ($40,000 – $7,500, subsidy) on a Chevy Volt and having to charge it every day, etc., one can just as “green” by driving a much less costly gasoline or non-plug-in hybrid car that achieves 37 MPG EPA Combined or better. Here are a few, unsubsidized, high mileage and non-plug-in hybrids:


Honda Civic; City 29, Highway 41, Combined 33

Volkswagon Jetta; C 30, H 42

Chevy Cruze Eco; C 28, H 42, Combined 33 

Volkswagon Passat; C 31, H 43

Honda Civic Hybrid: C 44, H 44

Ford Fusion Hybrid; C 47, H 47

Toyota Prius Hybrid; C 51, H 48, Combined 50




A more rational approach would be for the EPA to follow the European method based on grams/kilometer. It is more realistic, less deceptive, and less confusing.


For a European car sold in the US, the EV mode would be based on the US grid CO2 emissions intensity of 1.154 lb CO2/kWh, which would be slowly decreasing as more CO2-free energy is added to the grid.


The gasoline mode would be based on the energy in a gallon of fuel, such as gasoline, a blend of ethanol and gasoline, diesel fuel, etc.


Each light duty vehicle would have its CO2 emissions stated in grams/mile and grams/km. 


In Europe, road transport contributes about one-fifth of the EU’s total emissions of CO2. Emissions of CO2 from road transport increased by nearly 23% between 1990 and 2010; without the economic downturn, the increase would have been greater. Transport is the only major sector in the EU where CO2 emissions are still increasing.




Light-duty vehicles are a major source of greenhouse gas emissions, producing about 15% of the EU’s emissions of CO2.


Following up on a European Commission strategy adopted in 2007, the EU has put in place a comprehensive legal framework to reduce CO2 emissions from new light duty vehicles as part of efforts to ensure it meets its greenhouse gas emission reduction targets under the Kyoto Protocol and beyond.


The legislation sets binding emission targets for light-duty vehicles. As the automotive industry works towards meeting these targets, average emissions, gram/km, have decreased each year.


In July 2012, the Commission proposed legislation setting out the modalities for implementing the 2020 targets.

The Commission plans to issue a communication at the end of 2012 seeking stakeholders’ views on post-2020 emission targets for new light-duty vehicles. The intention is to ensure that CO2 emissions from light-duty vehicles continue to be reduced while giving the automotive industry the certainty it needs to carry out long-term investments and develop innovative technologies. Any proposal of future targets will be based on a thorough assessment of their economic, social and environmental impacts.




In 2008, after dire predictions of factory closures and mass job losses, the European Union agreed to a limit of 130 g of CO2/km to be phased in between 2012 and 2015, and to 95 g/km by 2020. This compares with an EU average of 160 g/km in 2007 and 135.7 g/km in 2011.


The 2015 target equates to 5.6 l/100 km of gas, or 4.9 l/100 km of diesel. 

The 2020 target equates to 4.1 l/100 km of gas, or 3.6 l/100 km of diesel.


Germany is objecting, because its lower-mileage luxury vehicles are a major percentage of its production.




For vans the target is 175 g CO2/km by 2017 and 147 g/km by 2020. This compares with an average of 203 g/km in 2007 and 181.4 g/km in 2010.


The 2017 target equates to 7.5 l/100 km of gas, or 6.6 l/100 km of diesel. 

The 2020 target equates to 6.3 l/100 km of gas, or 5.5 l/100 km of diesel.


Penalty Payments for Non-Compliance; applies to cars and vans


If the average CO2 emissions of a manufacturer’s fleet exceeds its limit value in any year from 2012, the manufacturer has to pay an excess emissions premium for each car registered. This premium amounts to 5 euro for the first g/km of exceedance, 15 euro for the second g/km, 25 euro for the third g/km, and 95 euro for each subsequent g/km. From 2019, the cost will be 95 euro from the first gram of exceedance onwards.


CO2 Emission Labelling of Cars and Vans


To help drivers choose new cars with low fuel consumption, EU legislation requires Member States to ensure that relevant information is provided to consumers, including a label showing a vehicle’s fuel efficiency and CO2 emissions.


Heavy-duty Vehicles


Heavy-duty vehicles (HDV) – trucks and buses – are responsible for about 25% of CO2 emissions from road transport in the EU and for about 6% of total EU emissions. Despite some improvements in fuel consumption efficiency in recent years, HDV emissions are still rising, mainly due to increasing road freight traffic.


The Commission is currently working on a comprehensive strategy to reduce CO2 emissions from HDVs in both freight and passenger transport.


Fuel Quality


Fuel quality is an important element in reducing greenhouse gas emissions from transport. EU legislation requires the greenhouse gas intensity of vehicle fuels to be cut by up to 10% by 2020.









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Bobbi O's picture
Bobbi O on Feb 13, 2013 2:07 pm GMT

  This is rear view thinking  at the worst! Using existing lbs. of CO2 per Kwh is assuming no serious reduction in CO2 from the grid is in the future. Likely improvements in technology not yet incorporated in utility scale electricity production makes your calculations worthless.Critics have few creative talents and generally make a living by finding reasons to say no.

Thomas Garven's picture
Thomas Garven on Feb 13, 2013 4:13 pm GMT

I am not sure how much this would effect things but doesn't each section of the country have a different CO2 content or component in their grid and isn't the time of day also important?

For example, the ISO CA grid I believe is less carbon intensive than say the Southeastern grid servicing say Kentucky.  Isn't the electrical grid in TX with its wind component [when it blows] cleaner than say the OH grid which may be more coal intensive.  Wouldn't the calculations also be different based on the time of day?  For example, when coal power is reduced or when hydro power becomes available and replaces that source.  I am just thinking that using one value is only a snapshot in time and the time the snapshot is taken can make a significant difference in the outcome.  For example, when the sun comes up and 3,000 MW of solar comes on line feeding CA from AZ and the Central Valley.     

Very Interesting and well written piece but I am not sure as a consumer how any of this would be of value to me when I go shopping for a new vehicle.  I think I will stick with the old MPG or MPGe number[s] until someone can prove to me there is something better.      

Bobbi O's picture
Bobbi O on Feb 13, 2013 5:08 pm GMT

  Your 40 years of experience was  during a period of relatively low motivation for change; in fact , a large part of that period was regressive. New Imperatives of climate change , high oil prices, national security, and  technology reaching critical mass will change the math from linear to exponential.

Rick Engebretson's picture
Rick Engebretson on Apr 7, 2013 2:38 pm GMT

Willem, you show rare modesty elaborating the improvements in US utility (and other energy) services during “your time.”

We value critics with better ideas we can understand. We are right to fear those that want to tear down our life support system and somehow rebuild something we have never seen work.

It wasn’t perfect and forever. But it was best in the world for your time.

Thomas Garven's picture
Thomas Garven on Apr 7, 2013 3:04 pm GMT

I will be closing my postings on this story by taking some liberty with the work of J. Leno and his man on the street segment or whatever it is called.  With the vast majority of the populace not able to identify who the Vice President is when shown his picture, asking them to understand the concept of grams/mile is well, really a reach.

While Willem’s posting is technically correct in many areas it lack one thing.  Some approach or technique to get the attention and support of the American people to accept the reasoning.  When people go to purchase a vehicle they are probably more interested in style, performance, luxury and miles per gallon and not necessarily in that order.  Some people will say; oh man that car looks hot and I want it.  Others may say and argue that they really do need 400 h.p. to move their behinds from point “A” to point “B”.  Still others, like a Prius owner for example probably buy the vehicle because it gets 50+ mpg.  

Willem’s posting here is certainly o.k. since most individuals on this form have at least some concept of the points he is trying to make.  It might however be better placed with officials and representatives from the EPA and automotive industry.  In that venue his posting might get the discussion it deserves.    

Thank you for reading my posting and have a great day.

Volt Owner's picture
Volt Owner on Jul 26, 2014 12:44 am GMT

For those interested in the energy mix of their area:


I belive this is based on 2012 data, so not completely up to date with recent coal to gas conversions.

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