2012 Toyota Prius Plug-In: Parsing The EPA Efficiency Sticker

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We all understand what miles-per-gallon means for a gasoline car.

And we can readily grasp the range in miles of an electric car.

But when a car has both a gasoline engine and an electric motor, things can get complicated.

The standard 2012 Toyota Prius is rated at 50 miles per gallon, and at best it has 1 mile or so of all-electric range (under light acceleration up to, say, 30 mph).

But the new 2012 Toyota Prius Plug-In Hybrid has a larger lithium-ion battery pack that plugs into a wall socket to recharge (in about 3 hours), giving it a multiple of that electric range.

It doesn't necessarily run continuously on electric power until its pack is empty, however--unlike the Chevy Volt range-extended electric car.

Instead, the Prius Plug-In will run electric-only up to speeds of 62 mph, potentially for 10 miles or a bit more, if the driver accelerates carefully and not too hard.

But as we noted in our brief drive of the plug-in Prius production version,

As we found out during a couple of short test drives last month in San Diego, this means that--even if you have 10 miles of electric range remaining--an uphill freeway on-ramp will switch on the engine at full howl when you floor the accelerator to merge into fast-moving traffic.

So how exactly does a manufacturer explain that on the EPA-mandated window sticker showing fuel efficiency?

With input from Greg Thome, a communications manager at Toyota, and our readers John C. Briggs and Dennis Chin, here's how we parse some of the ratings on the 2012 Toyota Prius Plug-In Hybrid window sticker.

2012 Toyota Prius Plug-In Hybrid window sticker showing EPA fuel efficiency ratings

2012 Toyota Prius Plug-In Hybrid window sticker showing EPA fuel efficiency ratings

Enlarge Photo

(A) 95 MPGe:This is the car's efficiency while operating on a mix of gasoline and electricity--that is, on a mix of power from the charged battery pack, supplemented by engine torque under high power demand.

In short, using electricity to power an electric motor puts much more of the energy toward turning the wheels than does burning gasoline. The "MPGe" measure looks at the distance traveled on electricity with the energy content of 1 gallon of gasoline. The EPA says it will travel at this blended MPGe efficiency for 11 miles (see point D below).

(B) 50 MPG:This is the Prius Plug-In's gas mileage when it's operating in "gasoline" mode after the pack is depleted. Under those circumstances, the plug-in hybrid has the same gas mileage as a standard 2012 Prius liftback that doesn't plug in.

(C) $7,600: This is the amount the EPA says an owner will save in combined fuel costs over five years compared to a vehicle with the average of all fuel efficiencies of vehicles rated by the EPA--or more than $1,500 per year.

(D) 11 miles: This is the EPA's estimated driving range for "blended operation" on a combination of electricity (from a fully charged battery pack) and gasoline over a blend of city and highway driving. That is, it's how far you'll travel before the battery pack is depleted and the Prius Plug-In reverts to behaving like a standard Prius hybrid.

(E) 6 miles: But--and here's the kicker--in very, very small type, the EPA says the car's "All-Electric Range" is 6 miles. This is an "adjusted composite" based on their particular blend of city and highway test cycles, which includes a hill simulation at about 6 miles. You may get more all-electric range at lower speeds, or less if you drive fast or uphill.

(F) 540 miles: This is the EPA's estimate for the total range the Prius Plug-In will achieve until both its power sources are depleted. The comparable figure for a regular gasoline-only Prius is 536 miles.

One final note: The Prius Plug-In Hybrid requires the driver to select "EV" mode to use battery power when the car starts up.

If a driver doesn't do so, the car operates like a regular Prius right off the bat. This allows drivers to save their EV miles and use them in specific locations.

It would appear to us that the EPA tests assume the "EV" button is selected at the start, and the car is driven continuously until the pack is depleted.


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Comments (18)
  1. Thanks for the rundown.
    I have to say that this sticker still confuses me. On the Volt, EPA declined to say what the projected annual running costs are. I guess that is because you would have to assume a mix of electricity and gasoline usage.

    Somehow, the EPA had no such reservations for the blended mode hybrids and assigned a $1000/year fuel costs to the PiP versus $1150/year for the standard Prius. So I am guessing that owner of the PiP are not doing it for the $150/year savings, but then again that is probably true for many Prius owners.

    Still, perhaps this represents a reasonable why to transition into an all electric future.

  2. I believe the EPA did add the yearly fuel costs to the 2012 Volt sticker and it is somehow $1k, just like the PIP. I really don't see how the two could be the same. http://www.chevroletvoltage.com/index.php/volt-blog/18-volt/2501-2012-chevrolet-volt-epa-label-revision.html

  3. Interesting. Well my source was FuelEconomy.gov
    and they show $650/year electric only and $1650/year for gasoline only.

    If you are skeptical of exactly $1000/year for the PiP and the Volt, I am equally skeptical of $650 for electric and exactly $1000 more ($1650) for gasoline. Is someone "guessing."

  4. This issue is going to be extremely confusing for the average buyer and the EPA clearly isn't helping. I think orgs like Consumer Reports need to step up with some comprehensive, real-world testing of plugin vehicles in various scenarios to give people a better idea of the cost/gas savings they can expect.

  5. I have to say that even providing a "gasoline only" yearly cost for the Volt seems misguided. Who buys a Volt and then drives it exclusively on gasoline?

  6. Here's another way to look at the numbers. If you drove the PIP everyday for a year and averaged 11k miles/year, you are, at best, displacing about 20% of your miles (2190 miles) from gas to electricity. Better than nothing, but definitely a different animal than the Volt, where drivers are getting 90%+ electric driving.

  7. That is the problem with all these calculations, there is always a "what if."
    What if I charge up both at home and at work. Maybe then I can displace 40% of my gasoline miles. But I think your once a day charging scenario is probably more likely.

  8. I really hope someone is able to create something similar to voltstats.net for the PIP. That will be the best source of info. Though, somehow I suspect that Toyota will keep that info locked down.

  9. All-Electric Range" is 6 miles.
    Six miles? Is it even worth plugging it in? In a Leaf, I could plug in once every two or three days.

  10. Think of it like a training bra. Sure the young lady doesn't really need it, but it gets her in the habit. The Plug-in Prius can get us in the habit of plugging in. :)

  11. All this shows is how superior the Volt is, in comparison. Once you've adjusted for the difference in tax, the price difference between a loaded Prius plug-in and a Volt is also only $2,000. The Volt is so good that BMW is now copying it: http://www.thestreet.com/story/11451833/1/how-the-chevy-volt-became-a-bmw.html

  12. Can we wait a few month to see the initial PiP sales numbers before declaring the Volt a winner?

  13. A few comments:

    AER 6 miles - This is the number of miles before the gas engine started, not when the battery charge ran out.

    95 MPGe with 11 miles range - That's when the battery charge depleted with 0.2 gallons consumed. Note, when it is "depleted", it still has a few EV miles (with 8 full bars) like in the standard Prius.

    50 MPG - The breakdown of city/highway is 51/49. Highway MPG is 1 higher.

    With the realworld data from the owners, many are getting about 13 miles per charge. Those 13 miles may not be continuous as they use EV miles that best fit their commute -- from home to highway and then the exist to work.

    Owners are also able to charge multiple times a day, raising the total EV to HV ratio (displayed onscreen real-time).

  14. The default is EV mode.

    Everyday when I pull my new Prius PHV out of the garage, it's automatically in EV mode until I accelerate onto the 70 mph highway nearby. And when I have switched to HV mode to retain EV capacity for later, the range value actually climbs up a little as I drive... something most people never considered would happen, since they tend to forget how persistent the hybrid system is even while still delivering 50 MPG.

    Yesterday's commute and running around afterward came to 58 miles. With only a single charge the evening before, the result was 71 MPG.

    On the day when I only drove the commute and recharged at work too, the result of those 36.8 miles driven was 144 MPG.

  15. Here's a thought. Why do we need over inflated government organizations' like the EPA and DOT to regulate vehicles that are not high pollution emitters'. These bureaucratic mechanisms stand in the way of progress, and cost new car consumers more money.Let's get the clock watchers' and office holders out of our lives, once and for all.

  16. 1. The EPA Rule says “The new labels require overall metrics for 5-year fuel savings, annual fuel cost, CO2 emissions, and the fuel economy and greenhouse gas rating. EPA has chosen to use the UF approach to calculate the overall values for these metrics.”

    What number did you assume for UF (Utility factor) in this case for the Prius PHV?

    2. The EPA’s sample label for “Plug-in Hybrid Electric Vehicle Label, Blended PHEV” shows “All Electric Range = 0 miles”. There should be no “All Electric Range” in the blended PHEV.

    3. From the “95 MPGe” value in the “electricity + gasoline” range, it seems that the Prius PHV travels abut 82% of 11 miles distance by electricity and the rest (about 18%) by gasoline. How did you get the "6 miles"?

  17. @Masao: To your Qs 2 + 3: Look at the photo of the label in the article above. The EPA quite clearly designates, "All electric range = 6 miles"--as the article discusses.

  18. Thanks John, I understand now. Dennsi Chin already wrote about this.

    The EPA §600.311-12 describes "for the vehicle that use combined power from the battery and the engine before the battery is fully discharged," "establish an all electric range by determining the distance the vehicle drives before the engine starts, rounded to the nearest mile."

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