Green

How the EPA’s bogus mileage ratings are hurting electric car sales

Above: A Prius Plug-In Hybrid, recharging in the author's driveway.

Image Credit: Dylan Tweney/VentureBeat
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Sometimes, the advantages of a new technology are unclear because people are evaluating it with an outdated metric.

Case in point: miles-per-gallon-equivalent (MPGe) ratings for alternative-power cars, including hybrids, plug-in hybrids, and electric cars.

This has become clear to me over the past few months since my family started driving a plug-in hybrid. We’re saving an enormous amount of money by driving on electricity instead of gas, but none of that savings was obvious before we bought the car.

Traditional miles-per-gallon ratings have been a key part of automobile marketing for decades. Indeed, it’s one of the things that dealers are required to put on the window stickers for new cars.

But how do you handle a car that consumes fuel by the kilowatt, not the gallon?

The misguided MPGe

The Environmental Protection Agency and Department of Transportation addressed this with the MPGe figure, which has been mandatory on window stickers since 2011. But this rating is artificial, and it doesn’t actually help buyers estimate the true impact of buying an electric or plug-in hybrid car.

What does it mean that an electric car like the Nissan Leaf has an MPGe of 126 city/101 highway or that the Tesla Model S gets 95? These cars never consume gasoline at all, so those figures are purely imaginary. It’s hard to translate these numbers into a measure of what the economics of the cars really are.

Sample car window sticker with MPGe rating.

Above: Sample car window sticker with MPGe rating.

Image Credit: Green Car Congress

More helpful are the figures in smaller print next to the MPG ratings: kilowatt-hours (kWh) per 100 miles on electricity and gallons of gas per 100 miles on gas. But few consumers know this data exists, let alone where to look for it or how to use it. (Complicating things: The fact that this is stated in amounts per 100 miles instead of per mile.)

In my case, my family’s new car is a 2014 Toyota Prius Plug-In. In the past few months, we’ve seen an average fuel economy of about 45 mpg, a little off the official efficiency of 50 mpg in hybrid mode. Our driving includes a combination of around-town trips (taking the kids to school, shopping, errands, and so forth) and one long-distance jaunt for a total of about 3,500 miles.

In its plug-in, electric vehicle mode, the Prius has an official MPGe rating of 95. Sounds pretty good, right? But what that actually means depends on your use case.

Its range on purely plug-in electric power is small: just 10 or 11 miles. That’s not much for most American consumers, but it’s plenty for us most weeks. I commute via bike and train, and my wife works at home, so the car’s main uses are for taking the kids to school and running errands.

The upshot: Many days we burn no gas at all, or almost none. We plug in the car overnight, using a standard 110-volt outlet on the porch (as with most electric cars, the Prius charges just fine on household current). Using the Prius’s capability to schedule its recharge for specific hours, we have it recharge in the early-morning hours, before 6 a.m., when the rates are the lowest.

What driving on electricity actually costs

It takes about 3 kWh to recharge the Prius. At PG&E’s early-morning rates on our tiered plan, that’s about 20 cents to 25 cents’ worth of electricity. (Hint for northern California readers: PG&E offers a special plan for electric car owners, but the rates aren’t actually that good. Its best rates are available through its Time of Use plan, which charges higher rates during the day but very low rates overnight.)

As a result, the economic impact is substantial. Ten miles in our old car, a 6-cylinder Mazda minivan that gets 20 mpg at best, takes about half a gallon of gas, which at California’s current gas rates costs us about $2.10, or 21 cents a mile.

In the Prius, burning gas, 10 miles costs us about $1.05, or a little more than 10 cents a mile.

But on electricity, that 10-mile all-electric range costs no more than 25 cents, or under 2.5 cents a mile.

In other words, on a cost-per-mile basis, electricity is roughly one-tenth the cost of gasoline.

Clearly, this gives us an enormous incentive to run the car on electricity instead of gas. We’ve been able to save about $60 per month this way. Add in the savings from the increased efficiency on gas-powered driving (compared to our old car) and our savings are over $100 per month, or almost half the cost of the car’s lease.

The savings would be less if our daily driving range was longer, as it is for most American families, because the cost of electricity would become a smaller proportion of our overall driving cost.

As a result, enhancing the plug-in range will be critical for Toyota if it really wants to sell more plug-in hybrids.

Regardless, none of these economic advantages are obvious to most car buyers, since the MPGe rating obscures them.

Complexity and opacity rule

Adding to the complexity are fluctuating gas prices, introducing uncertainty into the cost-per-mile calculation for internal-combustion driving. And electricity prices are not only variable, they are not at all transparent. You can’t look them up on PG&E’s website. So it is almost impossible to make this calculation until you actually drive the car home and try it out for a while and then look at your utility bill.

No wonder electric cars and plug-in hybrids are not taking over. As long as outdated means of measurement obscure their true economic impact, and as long as the market for electricity remains so opaque, few people will be able to figure out whether they’re worth it.

If the EPA wanted to make a meaningful difference, it would force some transparency into electricity pricing and mandate estimated cost-per-mile calculations on window stickers instead of MPGe.

Better yet, it could create an app that people could use to perform their own calculations based on their location, utility company, and the current price of gas in their area.

Or, even better, car manufacturers like Toyota, Nissan, and Tesla could make their own apps to simplify these calculations easier for would-be purchasers.

The good news is that electricity-powered driving is very much worth it — if you can buy a car whose range fits your needs.

More information:

A Japanese multinational automaker headquartered in Toyota, Aichi, Japan. In 2010, Toyota employed 300,734 people worldwide, and was the third-largest automobile manufacturer in 2011 by production behind General Motors and Volkswagen G... read more »

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18 comments
Tom Biegala
Tom Biegala

EPA's MPG ratings are NOT bogus. In fact they're completely accurate and the best apples to apples metric one can use given the constant fluctuations in both gasoline and electricity prices. It's not the EPA's job to run a cost-benefit analysis for the consumer. That's the consumer's job (or the automakers' job if they were smart marketers).


It all comes down to how much energy (in kilo-Joules) it takes to travel a certain distance. In the case you outline, it takes 3 kWh (10,800 kJ) to travel 10 miles in the Prius and 0.5 gallons (65,880 kJ) to travel the same distance in the Mazda minivan. The minivan requires about 6x more energy to travel the same distance so the Prius' MPG should be 6x greater, which matches the estimates you gave above (126 mpg versus 20 mpg).

Aaron J Bates
Aaron J Bates

Curious what the motivation for a plugin car was. Economic, sustainability or both.

Thomas K
Thomas K

Mileage has become one of the most important considerations for people buying/leasing new cars. I chose my last car based on EPA mileage estimates of 50 MPG. In reality, the mileage has never been higher than 35 MPG, on a good day. The difference in fuel costs between expected and actual mileage adds up to $thousands more per year.

So, if EPA wants to lie about MPG, maybe they can reimburse all of us the difference? But beyond the EPA, car manufacturers had better understand that consumers have been getting burned by false MPG estimates long enough now, that they'll likely avoid those manufacturers when they go to purchase their next vehicle. They tried getting more sales by lying, and now they'll get less. Brilliant example of short-sighted corporate economics.

joe blough
joe blough

you can't really blame the EPA for trying - your article shows that understanding the power consumption of EVs and PHEVs is pretty complex.


also in my case (leaf + plug in prius) the time-of-use plans would end up costing me a fortune, since the "always on" power consumption of my house is pretty high. yes, i know PG&E will let me install a 2nd meter for the cars, but for that $2k-$3k cost i can buy a lot of electricity.


bottom line then for those of us that can't go on ToU is that electricity costs $0.36/kwh and so now the cost per mile of the leaf is closer to a regular prius getting 48MPG when gasoline costs about $4/gal. there are of course other external costs involved in the gas car, so the EV comes out ahead, but not necessarily as far as my wallet goes.


ironically northern california is not really the best place to own an EV. in the midwest where the electricity is practically free and the terrain is flat, things would be much better.

Curtis Murphy
Curtis Murphy

"Add in the savings from the increased efficiency on gas-powered driving (compared to our old car) and our savings are over $100 per month, or almost half the cost of the car’s lease."

I'd love to know where you can lease a Prius plugin for $200 a month. I can't even find a bi-weeky payment that low in my area. Please link us all to the dealers website or post the address.... Or correct the article.

Bryan Seigneur
Bryan Seigneur

I like to tell my friends that I pay 6.8 cents per kwhr on my utility's nighttime EV rate, and I drive 5 miles per kwhr*.  6.8 cents, 5 miles.  


Suck it, BP, Exxon, Chevron, all of you, suck it.

*(Driving in town reasonably.  In a 2014 LEAF.  Hot dogging a lot (I love to show off and beat sports cars off the line to 45mph) it goes down to 4.5, and taking a trip at 75mph it approaches 4 miles per kwhr.)

SFCitizen
SFCitizen

@dylan20 So sales would have "taken off" but for mpge? Sounds absurd.

teds027
teds027

@dylan20 Noticed the same @ Tesla this week... completely unclear how they arrived at $900 a year cost or the 'premium' fuel savings

Dylan Tweney
Dylan Tweney moderator VB Staff

@Jason King Jason, thanks for taking time to reply! And for the link to your rates (I had difficulty finding it myself).

dylan20
dylan20

@SFCitizen maybe not. But how can you sell something whose main benefit is completely obscured?

SFCitizen
SFCitizen

@dylan20 3. ...people already know that what they pay for electricity will be dramatically lower than what they pay for gas. IMO

SFCitizen
SFCitizen

@dylan20 2. ...but consumers preferred the MPG equivalent option. Plus, they needed a way to give EVs credit for CAFE. In any event, I think

SFCitizen
SFCitizen

@dylan20 I think people know what they're getting into. The govmint actually is promoting EVs and plug-in hybrids. They focus grouped kwh...