Monday, September 22, 2014

Recent Improvements in Fuel Efficiency


Recent Improvements in Fuel Efficiency

The EPA provides annual updates of fuel economy of newly manufactured cars and light trucks.   This post discusses the implications of data released in the latest report on Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 through 2013.




Problem:  The fuel efficiency trends report has the following data on manufactured adjusted fuel economy in 2011 and 2013. 


2011
2012
Difference
Mazda
25.0
27.1
2.1
Honda
24.1
26.6
2.5
Toyota
24.1
25.6
1.5
VW
26.0
25.8
-0.2
Subaru
23.9
25.2
1.3
Nissan
23.3
24.1
0.8
BMW
22.7
23.7
1.0
Ford
21.1
22.8
1.7
GM
20.7
21.7
1.0
Daimler
19.1
21.1
2.0
Chrysler
19.4
24.1
4.7


What is the average, median standard deviation, range and inter-quartile range of fuel efficiency improvement for each manufacturer?  

Assuming an average vehicle miles driven of 14,000 miles per year what is the reduction in first-year gas consumption for each manufacturer?

The EPA also reported that overall mpg (for all cars on the market) went from 22.4 to 23.6.   What is the reduction in total-first-year gas consumed for all new cars sold assuming an average miles driven of 14,000 and 12,000,000 new vehicles?

Answer:  Below are the statistics (median, mean, standard deviation,   ….) asked for in part 1.


Fuel Efficiency Improvements 2011-2012
2011
2012
Difference
Mean
22.7
24.3
1.7
Median
23.3
24.1
1.5
STD
2.3
1.9
1.2
Q1
20.7
22.8
1.0
Q3
24.1
25.8
2.1
Min
19.1
21.1
-0.2
Max
26.0
27.1
4.7
Inter-quartile Range
3.4
3.0
1.1
Range
6.9
6.0
4.9



Some Highlights:

All but one of the car manufacturers realized improved fuel efficiency between 2011 and 2012.  VW, the one exception, already had fairly high fleet fuel efficiency.

50% of the firms realized a fuel efficiency improvement of 1.0 mpg at Q1 to 2.1 at Q3.


The reduction in gas consumed:

In order to get the reduction in gas consumed at 14,000 miles divide 14,000 by mpg in each year and the subtract 2012 number from 2011 number.



Reduction in Gas Consumed at 14,000 miles
2011
2012
Difference
Mazda
560.0
516.6
-43.4
Honda
580.9
526.3
-54.6
Toyota
580.9
546.9
-34.0
VW
538.5
542.6
4.2
Subaru
585.8
555.6
-30.2
Nissan
600.9
580.9
-19.9
BMW
616.7
590.7
-26.0
Ford
663.5
614.0
-49.5
GM
676.3
645.2
-31.2
Daimler
733.0
663.5
-69.5
Chrysler
721.6
580.9
-140.7


Highlights:

The simple first-year average reduction in gas consumed for the 11 firms was 45 gallons  (negative sign is reduced use.)  

Cars at VW consumed 4.2 gallons more.

The largest gallon reduction occurred at Chrysler 140.7.   Note that Chrysler had a fairly low base and a large improvement.   (I suspect that the breakup between Chryslers and Daimler was motivated in part by some side effects of fuel efficiency regulations.  Perhaps we shall talk about this in a future post.)

Overall Effects

The overall first-year effect on gas consumption is laid out in a table below.

Basically we calculated miles driven and divided by miles per gallon in 2011 versus 2012.


First-Year Reduction in Gas Consumed From New Vehicles
Miles Driven
14000
Annual Vehicle Sales
12,000,000
Total Miles Driven
1.68E+11
2011 mpg
22.4
2012 mpg
23.6
2011 Gas Consumed
7,500,000,000
2012 Gas Consumed
7,118,644,068
Reduction in Gas Consumed
381,355,932
% Reduction
5.1%
Gallons Per New Vehicle
31.8


The first-year reduction in gas consumption stemming from the 2012 reduction in fuel efficiency appears to have reduced gas consumption of around 381 million gallons in the first year of vehicle use. 

These calculations assume that adjusted EPA mpg figures accurately reflect on-road fuel use.  

Economists tend to be very skeptical about fuel efficiency regulations.   Progress under the regulations had been uneven over time.    But these reductions in fuel consumption appear to be good news for those who care about the environment.



The report also has some preliminary data for 2013.   Interested readers should analyze the 2013 data. 


















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