. "2 Vehicle Fundamentals, Fuel Consumption, and Emissions." Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press, 2010.
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Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles
The CAFE for light-duty vehicles is calculated from fuel consumption data using a “harmonic average.”2 The harmonic average in the CAFE standards is determined as the sales weighted average of the fuel consumption for the Urban and Highway schedules, converted into fuel economy. The average is calculated using the fuel consumption of individual vehicles times the number of vehicles sold of each model, summed over the whole fleet and divided by the total fleet.
TABLE 2-8 Engines Manufactured for Class 2b Through Class 8 Trucks, 2004-2008
2004
2005
2006
2007
2008
Engines Manufactured for Heavy-Duty Trucks
Cummins
64,630
79,100
91,317
65,228
75,307
Detroit Diesel
48,060
61,074
63,809
29,506
35,174
Caterpillar
74,224
86,806
97,544
33,232
20,099
Mack
25,158
36,211
36,198
18,544
16,794
Mercedes Benz
17,178
24,414
24,584
17,048
10,925
Volvo
12,567
19,298
23,455
9,850
8,822
Navistar
0
0
0
4
927
PACCAR
0
0
0
52
20
Total
241,817
306,913
336,907
173,464
168,068
Engines Manufactured for Medium-Duty Trucks
Navistar
373,842
382,143
357,470
335,046
264,317
GM
74,328
77,056
83,355
87,749
72,729
Cummins
14,900
15,162
16,400
20,615
27,664
Mercedes Benz
16,075
20,038
27,155
19,330
9,066
Caterpillar
42,535
42,350
45,069
14,693
6,269
PACCAR
0
0
0
9,020
5,694
Hino
671
5,001
7,489
6,230
3,062
Detroit Diesel
0
958
8
0
0
Total
522,351
542,708
536,946
492,683
388,801
Engines Manufactured for Medium- and Heavy-Duty Trucks
Navistar
373,842
382,143
357,470
335,050
265,244
Cummins
79,530
94,262
107,717
85,843
102,971
GM
74,328
77,056
83,355
87,749
72,729
Detroit Diesel
48,060
62,032
63,817
29,506
35,174
Caterpillar
116,759
129,156
142,613
47,295
26,368
Mercedes Benz
33,253
44,452
51,739
36,378
19,991
Mack
25,158
36,221
36,198
18,544
16,794
Volvo
12,567
19,298
23,455
9,850
8,822
PACCAR
0
0
0
9,072
5,714
Hino
671
5,001
7,489
6,230
3,062
Total
764,168
849,621
873,853
666,147
556,869
Because fuel economy and fuel consumption are reciprocal, each of the two metrics can be computed in a straightforward manner if the other is known. In mathematical terms, if fuel economy is X and fuel consumption is Y, their relationship is expressed by XY = 1. This relationship is not linear, as illustrated by Figure 2-2. In this figure, fuel consumption is shown in units of gallons/100 miles, and fuel economy is shown in units of miles/gallon. The figure also shows that a given percentage improvement in fuel economy saves less and less fuel as the baseline fuel economy increases. Each bar represents an increase in fuel economy by 100 percent, which corresponds to a decrease in fuel consumption by 50 percent. The data on the graph show the resulting decrease in fuel consumption per 100 miles and the total fuel saved in driving 10,000 miles. The dramatic decrease in the impact of increasing fuel economy by 100 percent for a high fuel economy vehicle is most visible in the case of increasing the fuel economy from 40 to 80 mpg, where the total fuel saved in driving 10,000 miles is only 125 gallons, compared to
2
Harmonic average weighted where Nn = number of vehicles in class n, FEn = fuel economy of class n vehicles and n = number of separate classes of vehicles.
where Nn = number of vehicles in class n, FEn = fuel economy of class n vehicles and n = number of separate classes of vehicles.