2005 September 13 Tuesday
Fuel Efficiency Of Hybrid Vehicles Overstated by EPA Tests

Consumer Reports claims that in their own testing they found that US Environmental Protection Agency measures of car fuel efficiency overestimate efficiency for most cars and especially for hybrids.

Automakers conduct the government fuel-economy tests on a laboratory dynamometer. They can use hand-built prototype vehicles, within the EPA rules, to maximize miles per gallon in simulated city and highway driving. “Anybody taking a test, you’re going to figure out what the rules are and figure how to optimize your chances of passing that test,” says Reg Modlin, director of environmental affairs for Daimler-Chrysler. “So in that sense, yes, everyone attempts to put their best face on for the test.”

By contrast, Consumer Reports testers check fuel economy on roads and on our test track. We buy models anonymously from dealers, as consumers do.

We gauge overall fuel economy from our city, highway, and mixed-driving tests. Overall, the gas-powered vehicles we studied delivered 9 percent fewer mpg on average than their EPA stickers claimed; diesels and hybrids, 18 percent fewer mpg than claimed. The numbers ranged from 21 percent better than the EPA sticker to 28 percent worse.

The discrepancy between our numbers and the EPA’s is increasing. For gas-powered vehicles, the shortfall was 6 percent for 2000-model-year cars that we tested, but about 12 percent for 2005- and 2006-model-year cars.

Big differences between claimed and actual city mpg were the main reason for the discrepancy in overall mpg. Our city mpg figures ranged from 13 percent better than the EPA sticker to 50 percent worse. On average, our highway mpg more closely reflected the EPA rating.

Ironically, six fuel-thrifty hybrids we tested had some of the largest discrepancies, mostly on city mpg, where real fuel economy ranged from 11 to 25 mpg below EPA ratings. City traffic is supposed to be the hybrids’ strong suit, but their shortfall amounted to a 40 percent deficit, on average. Still, hybrids won three of the best five spots in our tests for overall mpg, along with the diesel Volkswagen Golf and the all-gas Toyota Echo.

The Honda Civic hybrid has an EPA city rating of 48 miles per gallon but Consumer Reports found it achieved only 26 mpg on their tests. People who think they are going to save money overall by buying a hybrid are probably wrong even with today's gasoline prices.

Check out the Consumer Reports top 10 most fuel efficient cars tested. Also see their most and least fuel efficient cars by category. Note that the Volkwagen Passat GLS TDI (i.e. turbo diesel) beats the Honda Accord Hybrid. Also see their discussion on why their test results differ from EPA results.

Update: These results also make federal tax subsidies for hybrid purchases look more questionable. For the same number of dollars of federal expenditures I bet a far better way to spend money to reduce energy usage would be to make buildings better insulated.

Share |      By Randall Parker at 2005 September 13 12:04 AM  Economics Energy

Engineer-Poet said at September 13, 2005 8:35 AM:

Fuel savings depend not on differences in miles per gallon, but gallons per mile; differences become far more significant as the economy numbers fall.

Achieving a number as low as 26 MPG with a Civic hybrid probably requires perverse conditions or severely sub-optimal driving habits.  A CU tester would not live with the car and would not develop such habits.  This can make a serious difference; I achieved 40.7 MPG average over the last tank in my Passat TDI (rated 38 MPG highway, 26 MPG city).

A driver with a well-tuned foot in a HCH might achieve 35 MPG city.  If a conventional vehicle rated at 30 MPG city actually achieves 24, the difference is .0131 gallons/mile, which costs 3.93¢/mile at $3.00/gallon.  Over 50,000 miles this pays $1964, and in 200,000 miles (easily done in 3 years of taxi service) it would pay $7857.

I predicted that $2.50 fuel would be fodder for nostalgia.  Gasoline may get back down to that price, but it probably won't stay there; anyone who buys a hybrid as a bet that fuel will be upwards of $3.00 for most of its lifetime is unlikely to regret the decision.

Jody said at September 14, 2005 11:46 PM:

Partially defending the subsidy decision, it's my understanding that while hybrid's fuel economy isn't that much better, their emissions are much better. Lower emissions is a public good and needs incentives while fuel savings is mostly a private good and is appropriately handled by the market.

Randall Parker said at September 15, 2005 10:05 AM:


The emissions estimates are based on the fuel economy estimates. If the engines burn more fuel than EPA figures lead you to expect then the pollute more than the EPA estimates as well. They have no more advanced catalytic converters than other cars.


How you drive is obviously not typical. I suspect the Consumers Union folks tried to make their test drive more representative of how people really drive.

Engineer-Poet said at September 16, 2005 11:12 AM:

Oh, I know that most people don't drive as I do; the question is, how many of them will look at how much money they're spending at the pump and decide that it's time to learn?  The beauty of this is that it takes no investment in vehicles or roads at all.

Rich said at September 20, 2005 12:18 PM:

WRT hybrids, I tend to take a wait and see attitude. They don't have
a track record yet and their strengths and weakneses are not clear.

I do have a few reservations however.

Like, how well do they perform in cold weather states, in the winter?

On the freeway, it's just a regular car. I see no advantage if you're
mostly doing freeway driving.

It's a very complex system, and it's long-term dependability is an
unknown. Also I question the cost of repairs. How much is the first
major service gonna cost? What if one battery dies? What when they
all get weak? How much to have them replaced? How much does the voltage
regulator cost, it's gonna have to be bigger and handle more current
than a regular car.

Overall, the city numbers rather seem to disprove the concept, as this
is where it's supposed to shine. Why does it not do 60MPG in the city?

It's important to look to the cost of ownership, not just the cost at
the pump. While the cost of ownership may only be slightly higher initially,
I wonder if after one major service if it won't be much higher.

BTW, on my first drive, my 1994 Honda Accord got 39.5 MPG. The state of
CA has since added MBTE to the gas and now the mileage sucks. I don't
expect that hybrids do any better in this regard. But getting rid of
the additives to the gas would greatly reduce fuel useage.

Rich said at September 20, 2005 3:16 PM:

One more thing I forgot.

What will happen in an accident?

Gasoline is pretty neat in that only it's vapors burn.
Fires are not impossible in accidents, but they are
rare indeed.

Now hybrids have gasoline, but they also have many lead-acid
batteries. I'm not worried about the lead, but the acid.

There will clearly be lots more of it than in a normal car.
It has the potential to harm those involved in an accident,
rescue teams, the roads, and unless properly cleaned up,
residents of the area.

How much of a hazard is it? I don't know. But potentially
this could be a significant problem.

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