James Hrynyshyn is a freelance science journalist and communications consultant based in western North Carolina, where he tries to put degrees in marine biology and journalism to good use.
I just don't understand where the EPA is coming from when it assigns fuel economy ratings. The latest rankings are out and they just don't jibe with my driving experience. I'm not the most aggressive driver out there, but neither am I an expert hypermiler who keep it down to the speed limit and catches tailwinds. Yet I consistently get better mileage whatever I'm driving than what the EPA says the car gets. I always get better mileage. Always.
I know that when the EPA says: "it is impossible for one set of estimates to predict fuel economy precisely for all drivers in all environments" they mean it. But really, what explains such a consistent discrepancy?
Driving a 2009 Toyota Corolla, which seems to be best value for the money in the non-hybrid market (and probably the entire market), I get between 37 and 38 miles per gallon on the highway. This I know thanks to the fuel economy readout that is now standard on Toyotas. And yet the EPA rates it at 35 mpg highway.
Driving a 1999 Honda Civic I get between 25 and 27 mpg highway. The EPA's figure is 23 mpg.
Driving a 2006 Toyota Prius, I get at least 50 and more like 52 mpg highway and 65 or 60 in the city, while the EPA gives it just 45 highway and 48 city.
I suppose the best conclusion is the EPA drivers drive much more aggressively than I do. Maybe they're all a lot younger than me. But one would think that they would employ a variety of driving approaches and average the result, no?
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I seem to recall reading somewhere that the EPA intentionally lowballs the mileage estimates. Whether that is under pressure from auto companies for some reason or to reduce people who complain that their specific car doesn't do as well as the EPA says it should I do not know.
Posted by: Rev Matt | October 22, 2008 3:20 PM
aston martin db9 is listed under the minicompact category?
as a side note, they're just about right on with the city mileage of the smart, but way below my experience on the highway. they say 41. I say 52.
Posted by: peter | October 22, 2008 4:01 PM
I think they have tried to replicate the average aggressive driver. They used to catch a lot of criticism because the EPA milage was unrealistically high. Now I suspect they may have gone too far the other way.
Some numbers, when I bought the 07 Prius it was rated at 50highway and 60 city. The 08, and 09 models are unchanged, so the adjustment downwards has been very substantial. I am told that the average driver gets something like 46, so it may well be that the adjustments are realistic. The driving habits of the bulk of the population really are that wasteful!
Posted by: bigTom | October 22, 2008 4:02 PM
You live in NC where the weather is very middling for mileage- no super hot and no super cold. The EPA now turns the Air Conditioner on and the Heater on as part of its trials. If you drove a Prius in Minnesota in Winter with the heater on I guarantee you wouldn't be getting the milage you said. That is what is affecting the new numbers also. I also second bigTom. Watch the accelerations and decelerations of a lot of drivers. You can find out exactly what EPA does if you dig around enough, or at least you used to be able to 20 years ago. You might have to pay for a report, but I am guessing it is on the web nowadays.
By the way - why do you trust the mileage meter in your car for an overall start to stop mileage? Have you measured miles and gallons in and compared? Just a thought.
Posted by: Markk | October 22, 2008 4:37 PM
Here is the driving schedule that they use for the ratings.
http://www.fueleconomy.gov/feg/fe_test_schedules.shtml
If you accelerate or drive slower than these values, you'll get better mileage.
Posted by: Wayland | October 22, 2008 5:37 PM
I protest the use of "art" to mean "not science" in this title!
But aside from that, you're quite right. These estimates never seem to be realistic. I guess they'd just rather err on the low side.
Posted by: bioephemera | October 22, 2008 9:26 PM
MANMADE GLOBAL WARMING. JOKE or FARCE or POLITCAL POWERPLAY for $$? -all of the above.
Posted by: James is a Goober | October 23, 2008 9:53 AM
The tests are run on a stationary dynamometer, not on the road.
I always used to get poorer mileage than the EPA tests got.
Posted by: Larry Fafarman | October 29, 2008 1:17 AM
Here is the test procedure:
http://www.fueleconomy.gov/feg/how_tested.shtml
Posted by: Larry Fafarman | October 29, 2008 1:19 AM
The highway figure published by the EPA is based on a correction factor applied to the test procedure. This has been applied for at least 2 decades and was the result of the previous estimates being far too optimistic.
Just for the record, I got around 35 on the highway in a 1990 Honda Civic EX, compared with an EPA estimate of 33. I get 40 - 42 on the highway with a 2004 Honda Civic EX, compared with an EPA estimate of 38.
It also depends on the ambient temperature. In cold weather, the mileage will be considerably lower then in the summer.
Another factor to consider is that 30 years ago, the most economical driving speed was in the mid forties. In todays cars which are designed to be more slippery relative to air resistance then the cars of 30 years ago and have far more efficient engines, the most economical driving speed is in the mid fifties.
A further element is that it is more economical on the highway to drive in the summer with the air conditioner on and the windows closed then with the air conditioner off and the windows open. This is because of the design of vehicles relative to air resistance.
Posted by: SLC | October 29, 2008 10:02 AM
I was a bit embarrased when merely by changing my driving style a bit, my daily commuting mpg went from ~37 to ~50.
That's quite handy when diesel costs the equivilent of $9 a gallon..
Oh, and I never use the aircon. Mostly because putting the aircon on makes the engine warning light come on, admittedly..
Posted by: Andrew Dodds | October 30, 2008 11:31 AM
I do not trust the mpg indicator. My old Dodge truck almost always indicated higher mpg than I actually got based on miles traveled and fuel added. But there are others who think the current procedures give better estimates of gasoline-powered vehicles but underestimate the mpg of diesel-powered vehicles. On my 2001 VW Golf diesel I always get slightly higher (by about 1 mpg or about 2%) than the EPA estimate of that time.
Posted by: Mark P | October 30, 2008 11:33 PM
The tests are run on a stationary dynamometer, not on the road.
I always used to get poorer mileage than the EPA tests got.
Posted by: film izle | May 29, 2009 9:54 AM