Environmental Engineering Reference
In-Depth Information
Table 13.7
Energy efficiency in ton-mile/gal (tonne-km/L) for different conventional and long combina-
tion vehicle configurations in North America.*
Type
Gross vehicle
weight (kg [lb])
a
Payload weight
(Kg [lb])
b
Ton-mile/gal
Tonne-km/L
5-Axle tractor-semitrailer
27,273 (60,000)
12,273 (27,000)
85
32.3
5-Axle twin double
10,909 (24,000)
74
28.1
Rocky Mountain double
45,454 (100,000)
25,909 (57,000)
130
49.4
Triple trailer combination
23,864 (52,500)
125
47.5
Turnpike double
22,500 (49,500)
117
44.5
Rocky Mountain double
54,545 (120,000)
34,769 (76,769)
161
61.2
Triple trailer combination
32,727 (72,000)
157
59.7
Turnpike double
32,329 (71,125)
151
57.4
Turnpike double
63,636 (140,000)
40,909 (90,000)
173
65.7
*
See Figure 13.5 for vehicle configurations.
a
Gross vehicle weight (GVW) is the maximum allowable weight including the vehicle, cargo, and fuel.
b
Payload weight is the maximum load a vehicle can carry without exceeding the GVW.
Data from Tunnell, 2008.
in most cases. Therefore, the reader should consult regulations that apply in a particular case
and geographic area.
A study conducted by the American Transportation Research Institute in collaboration with
Cummins
®
simulated fuel consumption and emissions resulting from the operation of conven-
tional and long combinations typically found in North America. Results of this study pre-
sented in Table 13.7 demonstrate that as the length of the vehicles increases the cargo can
more likely be transported in one trip increases as well, which makes the fuel efficiency
(expressed in ton-mile/gal) to improve significantly. The 5-axle-twin configuration capable of
a payload of 24,000 lb (10,900 kg) has the lowest fuel efficiency in Table 13.7 with around 74
ton-miles/gal (28 tonne-km/L) and the highest efficiency corresponds to the turnpike double
with a payload of approximately 90,000 lb (41,000 kg) and an efficiency of 173 ton-miles/gal
(65.7 tonne-km/L) that correspond to an improvement in fuel efficiency of about 2.4 times.
The improvement in fuel efficiency when using long combination trucks is because when
most trucks are loaded their volume capacity is reached well before their maximum weight is
attained, so additional trailers permit the transportation of more freight with just a slight
increase in fuel consumption. On the downside, long combination vehicles have some disad-
vantages: they are not allowed in all places and special permits are required in most cases; the
higher than normal weight and length limit their circulation to main highways only; and other
restrictions such as suspension of operation during bad weather and rush hours.
Weight reduction and increased volumetric capacity
Weight reduction and increased volumetric capacity translate into better energy efficiency.
Lighter vehicles have lower rolling resistance, thus requiring less energy to operate the vehi-
cle. This saved energy can be used instead to push more cargo when volumetric space is avail-
able. The maximum gross weight of vehicles and volumetric dimensions are regulated. So any
actions that can be taken to reduce the weight of the vehicle and to increase the volumetric
capacity within those limits will contribute to improve the fuel efficiency.
A tractor trailer at a typical highway speed of 65 mph uses around 55 percent of the power
to overcome aerodynamic drag, 33 percent to defeat rolling resistance, and the remaining to
power auxiliary equipment and other losses. Below 50 mph, tires are the main factor in fuel
