CAFE Fleet Requirements
| |
19751 |
20012 |
Increase |
| Vehicle miles traveled |
1.328 billion |
2.781 billion |
109% |
| Registered vehicles 3 |
126,153,000 |
230,428,326 |
83% |
| Licensed drivers |
129,791,000 |
191,275,719 |
47% |
| Vehicles per licensed driver |
0.97 |
1.20 |
24% |
| Barrels of oil imported/day |
6,056,000 |
11,619,000* |
92% |
| Gallons of motor fuel consumed |
113.549 billion |
167.105 billion |
47% |
1 - When CAFE law was passed
2 - Most
recent figures available, except as noted
3 - Excludes
motorcycles
* - Preliminary government
number
CAFE Math
You might think that calculating CAFE would be a
straightforward task. After all, consumers can calculate their
own fuel economy by keeping track of the miles they drive
between fill-ups and dividing that number by the amount of
gasoline they purchase. But CAFE calculations are much more
complex.
Every configuration of each vehicle is rated on two
different test cycles representing highway and city driving.
Those different configurations of vehicles are called model
types. The tests precisely measure the amount of fuel
used. Engineers measure the emissions of hydrocarbons,
carbon
dioxide and carbon
monoxide during the test cycles and apply those numbers to
a complicated formula that calculates the amount of fuel
used.
A manufacturer's CAFE numbers for light trucks, domestic
cars and non-domestic cars are calculated through a
mathematical process called harmonic
averaging. The complex formula makes it difficult for
automobile manufacturers to compensate for lower-mileage
vehicles that are nevertheless popular with consumers.
Automobile manufacturers are responsible for meeting CAFE
standards for three separate
fleets — domestic cars,
non-domestic cars and light trucks. In other words, there is a
corporate average for each fleet, derived using harmonic
averaging.
Here's how it's done:
- The total number of each model type in a fleet purchased
by consumers is divided by the model's composite
fuel economy rating. (For example: 120,000 sales,
divided by 27.3 mpg, equals 4395.6). This calculation is
done separately for each model type in a fleet.
- The resulting numbers from those calculations are added
together.
- That total number is divided into the total overall
number of vehicles purchased within the fleet.
- The result is the corporate average fleet economy
number.
In essence, harmonic averaging doesn't really measure fuel
economy, but rather fuel consumption. It doesn't measure miles
per gallon, but gallons per mile. This is an important
distinction. Rather than having only one 40-mpg vehicle
averaged with one 20-mpg vehicle to equal a 30-mpg fleet
average, the harmonic averaging of the CAFE program requires
two 40-mpg vehicles to be averaged with one 20-mpg vehicle to
reach a 30-mpg fleet average.
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