Fuel economy (or
mileage) is the average
distance a vehicle can travel on a
specific
volume of gasoline. Common units to express fuel economy are:
- Miles per Gallon (MPG) ; the number of miles a car can travel on
a gallon of gasoline. A high MPG indicates a more efficient
performance of the vehicle.
- Kilometers per Liter (km/L); Sometimes (confusingly)
expressed as 1 : x, where x is the number
of kilometers travelled. This rating is the metric
equivalent of the MPG quantization that is common in the U.S.
- Liters per 100 Kilometers (L/100 Km). Another popular
measure for fuel economy. In this case, a higher quantity indicates a
lower fuel economy.
Converting the various units is easy: 1 MPG = 0.425 Km/L, 1 Km/L =
2.35 MPG. See table below.
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MPG km/L L/100 km
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5.0 2.1 47.0
10.0 4.3 23.5
20.0 8.5 11.8
30.0 12.8 7.8
40.0 17.0 5.9
50.0 21.3 4.7
60.0 25.5 3.9
70.0 29.8 3.4
80.0 34.0 2.9
90.0 38.3 2.6
100.0 42.5 2.4
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Government agencies, such as the U.S. Environmental Protection
Agency (EPA), as well as several automobile manufacturers often test
vehicles for their fuel economy. These are standardized tests that allow
for a direct comparison between different brands and models of cars. The
vehicles are tested in a laboratory by professional drivers, using a
test setup similar to a treadmill.
The EPA annually reports fuel economy estimates for most cars sold
in the U.S.; This data consists of two different estimates of the fuel
economy; a city, and a highway estimate.
The test used to determine the city fuel economy estimate
simulates a 7.5-mile, stop-and-go trip with an average speed of 20 miles
per hour (mph). The trip takes 23 minutes and has 18 stops. About 18
percent of the time is spent idling, as in waiting at traffic lights or
in rush hour traffic. 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 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 test is run from a hot start and
has little idling time and no stops (except at the end of the test).
Since the fuel economy estimates reported by the EPA are obtained in a
laboratory, the results are generally adjusted for actual driving
conditions on the road; i.e. the city estimate is lowered by 10%,
and the highway estimate by 22%.
Go to
http://www.fueleconomy.gov for more info,
and to find fuel economy data of various automobiles.