Re: EPA Mileage "estimates"
Panjandrum said:
Well, one thing to remember is that the advertised mpg ratings of vehicles are totally inaccurate. I don't know how they come up with these things, but nobody ever seems to get anywhere close to the mileage estimates in any vehicle. I suppose somebody somewhere makes a few financial "donations" to the good folks doing the tests, and *poof*, the tests somehow return ridiculously inflated mileage estimates. I don't see how these estimates could be so far off "accidently", if you see what I mean; It's just hard believe that the consistently incorrect estimates, which always favor the automobile manufacturers instead of the consumers, are "accidental" in any way.
When I look at the blatantly fraudulent claims, oops, I mean "mileage estimates" on the window stickers, I multiply by approx .75 (in other words, I assume I'll only get 75% of what they claim I'll get) and I've found that this is surprisingly accurate).
Just placed an order for a new Prius today, I expect to get in the mid 40s.
A brief description of the EPA test cycles is here:
http://www.fueleconomy.gov/feg/info.shtml#estimates
<blockquote>
How are fuel economy estimates obtained?
The fuel economy estimates are based on results of tests required by
the U.S. Environmental Protection Agency (EPA). These tests are used
to certify that vehicles meet the Federal emissions and fuel economy
standards. Manufacturers test pre-production prototypes of the new
vehicle models and submit the test results to EPA. EPA re-tests about
10% of vehicle models to confirm manufacturer's results. The vehicles
are driven by a professional driver under controlled laboratory
conditions, on an instrument similar to a treadmill. These procedures
ensure that each vehicle is tested under identical conditions;
therefore, the results can be compared with confidence.
There are two different fuel economy estimates for each vehicle in the
Fuel Economy Guide, one for city driving and one for highway driving.
To generate these two estimates, separate tests are used to represent
typical everyday driving in a city and in a rural setting. Two kinds
of engine starts are used: the cold start, which is similar to
starting a car in the morning after it has been parked all night; and
the hot start, similar to restarting a vehicle after it has been
warmed up, driven, and stopped for a short time.
The test used to determine the city fuel economy estimate simulates an
11-mile, stop-and-go trip with an average speed of 20 miles per hour
(mph). The trip takes 31 minutes and has 23 stops. About 18 percent of
the time is spent idling, as in waiting at traffic lights or in rush
hour traffic. The maximum speed is 56 mph. The engine is initially
started after being parked overnight. Vehicles are tested at 68 F to
86 F ambient temperature.
The test to determine the highway fuel economy estimate represents a
mixture of "non-city" driving. Segments corresponding to different
kinds of rural roads and interstate highways are included. The test
simulates a 10-mile trip and averages 48 mph. The maximum speed is 60
mph. The test is run with the engine warmed up and has little idling
time and no stops (except at the end of the test).
</blockquote>
I also suggest reading the following article (with plenty of citations
for source data):
http://www.bluewaternetwork.org/reports ... ehood2.pdf
"FUEL ECONOMY FALSEHOODS: How government misrepresentation of fuel
economy hinders efforts to reduce global warming and US dependence on
foreign oil" by the Bluewater Network, 2002
note that the tests were developed
in the 70s, with a ratio fudge-factor
set in the 80s... driving patterns
have changed a lot since the last
time the tests were updated.