Tuesday, October 7, 2014

Calculating fleet average fuel efficiency

Calculating fleet average fuel efficiency  

Question:   Below are the sales numbers and my rough estimate of the fuel efficiency for the top twenty selling vehicles in August 2014.   What is the fleet fuel efficiency for vehicles sold in August 2014?


Sales estimates and fuel efficiency estimates August 2014
Aug-14
Fuel Efficiency
Ford F - Series PU
59,863
22
Chevrolet Silverado PU
50,176
22
Dodge Ram PU
36,612
22
Honda Accord
32,956
34
Toyota Camry
28,507
35
Honda CR-V
23,722
31
Toyota RAV4
22,724
29
Honda Civic
22,263
36
Ford Escape
21,718
30
Ford Fusion
21,693
36
Nissan Altima
21,675
33
Toyota Corolla / Matrix
20,530
30
Hyundai Elantra
18,848
38
Chevrolet Cruze
18,415
38
Chevrolet Equinox
17,266
24
Nissan Rogue
17,229
30
GMC Sierra PU
16,763
22
Ford Explorer
15,795
23
Ford Focus
15,397
36
Chevrolet Malibu
15,186
34



Answer:   The fleet fuel efficiency is calculated with a harmonic average.   It is the ratio of the sum of total sales to the sum of the sales to fuel efficiency ratio of each vehicle. 

From the table below observe that total sales in the month of August 2014 is 497,388 vehicles.   The value of the vehicle sales to fuel efficiency ratio for the 20 vehicles is presented in the far right column of the table below.   The sum of these ratios is 17,882. 


The fleet fuel efficiency is 497,338/17,882 or 27.8.


Calculation of Fleet Fuel Efficiency for August 2014 Sales
Aug-14
Fuel Efficiency
Ford F - Series PU
59,863
22
2,721
Chevrolet Silverado PU
50,176
22
2,281
Dodge Ram PU
36,612
22
1,664
Honda Accord
32,956
34
969
Toyota Camry
28,507
35
814
Honda CR-V
23,722
31
765
Toyota RAV4
22,724
29
784
Honda Civic
22,263
36
618
Ford Escape
21,718
30
724
Ford Fusion
21,693
36
603
Nissan Altima
21,675
33
657
Toyota Corolla / Matrix
20,530
30
684
Hyundai Elantra
18,848
38
496
Chevrolet Cruze
18,415
38
485
Chevrolet Equinox
17,266
24
719
Nissan Rogue
17,229
30
574
GMC Sierra PU
16,763
22
762
Ford Explorer
15,795
23
687
Ford Focus
15,397
36
428
Chevrolet Malibu
15,186
34
447
Total
497,338
17,882

Caveats:  This estimate may be off, possibly far so.    There are many types of each model and each version of each model has its own fuel efficiency number.  The fuel efficiency estimates used above are quick estimates of the median for each model.

The EPA has reported recent improvements in fuel efficiency. 



This is good news but it is my understanding that corporate average fuel efficiency numbers are based on sales projections.

In the best of worlds I would be able to crunch statistics to confirm the EPA result.   But the EPA’s job is really data intensive and I don’t have access to this type of detailed information. 

Also, the EPA gives vehicle fuel efficiency of 100 mpg for any car that can use alternative fuel.    I do not know the impact of this rule on reported numbers.   I do know that this rule allows firms to produce more low fuel efficiency cars than they otherwise would be allowed to.  





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