Environmental Engineering Reference
In-Depth Information
Basic energy
components
Measures of energy use
Propulsion energy
per ton-mile
Terminal and
maintenance energy
Guideway
construction energy
Vehicle manufacture
energy
Energy used in
access
Circuity
Operating
energy
Line-haul
energy
Modal
energy
Figure 13.3
Energy components and measures of energy use utilized in the analysis of transportation
methods.
From Congressional Budget Office, 1982.
Transportation method and energy intensity
In transportation, energy intensity represents the energy spent to transport a specific mass of
cargo for a specific distance.
Energy used
[13.2]
Energy Intensity
=
Mass
×
Distance
The metric system (International System) measures the energy efficiency of freight in MJ/
tonne-km and the imperial system in Btu/ton-mile. The inverse of energy intensity is energy
efficiency, tonne
km/MJ, which is expressed usually as fuel efficiency in tonne-km/liter or
ton-miles/gallon. Calculation of energy intensity can be conducted in two ways:
⋅
1.
Energy intensity based on operating energy, by dividing only the propulsion energy used
by tonne of cargo and distance without including the weight of the vehicle.
2.
Energy intensity based on modal energy, by including all the energy used in propulsion,
maintenance, vehicle manufacturing, construction, the effect of circuity (unproductive
deviation of the vehicle to go from point A to point B from the theoretical straight line that
connects both points), access energy (amount of energy to move the cargo to and from the
transportation system), the guideway over which the vehicle moves (tracks and high-
ways), refinery losses and the energy used for empty movements, and for the noncargo
weight of vehicles (Fig. 13.3) (Congressional Budget Office, 1982).
Figure 13.4 present a comparison of energy intensity for different transportation methods
considering only operating energy. The lower part of the graph contains the transportation
methods with the lowest energy consumption, which are associated with the moving of bulky
and homogeneous materials at low to moderate speeds. The highest energy efficiency comes
with the cost of being slow and restrictive methods of transportation or serving only very
specialized functions as is the case of oil pipelines.
Cargo planes are the most energy-intensive transportation method, which is followed by
trucks. However, it is not unexpected becuse they both provide high levels of service. Planes
