Environmental Engineering Reference
In-Depth Information
when considering only operating energy. There is one exception though; truck transportation
has similar values for both modal and operating energy, which is likely to be due to different
assumptions made to estimate energy intensities.
In general, for all transportation methods, propulsion and circuity account for more than 70
percent of the energy during the life cycle of the transportation vehicle. For rail and barges
propulsion energy varies between 35 and 50 percent of the total modal energy used. Intercity
trucks and planes consume 60 and 90 percent, respectively, of the total modal energy on pro-
pulsion. Circuity is an important component of the total energy consumed by barges, rails, and
intercity trucks with 45, 35, and 20 percent, respectively. On the other hand, circuity accounts
just for 10 percent in planes and pipelines. In most cases, vehicle manufacture, guideway
construction, and maintenance accounts just for 10 percent of modal energy (Congressional
Budget Office, 1982).
There are other factors that affect energy intensity of transportation:
Planes spend large amounts of fuel during take off and until reaching cruising altitude, so
short hauls are going to be affected by this factor to a larger extent than long hauls.
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Fuel consumption in planes is influenced by the age of the equipment, engines, height,
weather, and weight of the cargo.
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Trucks burn more fuel going uphill than on a flat surface.
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Barges' fuel efficiency is affected when running upstream or downstream. As shown in
Table 13.3, a barge consumes double of energy when going upstream than when running
downstream.
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All vehicles are affected by running with a load or unloaded. In unloaded trucks, fuel con-
sumption is reduced by a factor of 0.7 (Dalzell, 2000).
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Bulk density of the transported material is important in energy intensity. Light materials,
or goods that do not pack well because of their geometry (like many food products), leave
empty spaces that affect the energy intensity significantly.
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Excessive packaging material, or heavy packaging, steals weight from the transported
product.
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Use of refrigeration increases the amount of energy needed to transport a product.
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Transportation vehicles are not 100 percent full all the time. Energy intensity depends on
the “vehicle capacity utilization.” Empty space increase the energy consumed per unit of
product.
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Transportation from grocery store to consumer's home
Transportation of food products from the retailer to the consumer's home when done in the
consumer's vehicle (in contrast to using public transportation) has much higher energy inten-
sity than the commercial massive transportation methods. Because there are variable dis-
tances from supermarkets to consumers, variable weights of groceries per trip, and different
fuel efficiencies for different vehicles, it is difficult to estimate how much energy is invested
in transporting food products. But by making some assumptions, the operating energy inten-
sity can be calculated. Assume that 10 kg (22 lb) of food products are transported per trip and
three types of vehicles: a sport utility vehicle (SUV) with a combined fuel efficiency of
15 miles/gal (6.3 km/L), a midsize sedan with a combined fuel efficiency of 24 miles/gal
(10.1 km/L), and a compact car with a fuel efficiency of 30 miles/gal (12.6 km/L). All the
vehicles use gasoline, which has an energy content of 115,000 Btu/gallon that is equivalent
to 121 MJ/gallon.
