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variables. This also provides a better indication of how efficiently energy is used to
provide personal mobility and distribution of goods. For example, from this
perspective, a bus carrying 20 passengers for 10 km (200 passenger-km) is less energy
intensive (more efficient) than the same bus carrying 5 passengers for the same
distance (50 passenger-km). Similarly, a fully loaded truck is less energy intensive
than the same truck carrying a partial load.
Vehicle Intensities: Energy use per vehicle-km by vehicle and fuel type is an
important indicator, as many standards for air pollution (and more recently, goals for
CO
2
emissions reductions) are expressed in terms of vehicle characteristics, that is,
emissions per vehicle-km.
Modal Intensities: Energy use per passenger-km or tonne-km should be disaggregated
by vehicle type, namely, two-wheel vehicle, automobile/van, bus, airplane, local and
long-distance train, metro (also known as ‘subway’ or ‘underground’), tram, ship or
ferry for passengers, and truck, train, ship or airplane for freight.
Note: Aggregate energy intensities for travel or freight are a meaningful summary
indicator whose value depends on both the mix of vehicles and the energy intensities
of particular types of vehicles. The energy intensities of public train and bus transport
per passenger-km are significantly lower than the energy intensities for automobiles
or air transport. Freight, rail and ship transport are commonly less energy intensive
than is trucking per tonne-km. It should also be noted that fuel consumption per
vehicle-km also depends on traffic conditions as well as vehicle characteristics.
The energy intensity of a vehicle depends on both capacity and capacity utilization. A
large vehicle that is fully loaded generally has lower energy intensity per tonne-km
than a fully loaded smaller vehicle, but a small vehicle fully loaded will have a lower
energy intensity than a large vehicle with the same load.
For some developed countries, typical load factors for private automobiles are 1.5
persons per automobile. For rail and bus, load factors vary from well below 10% (e.g.
United States city buses on average) to over 100% of nominal capacity at peak times
(in many developing countries during most of the day). Typical load factors for
trucking might be 60–80% of weight capacity when loaded, but trucks commonly run
20–45% of their kilometres empty, yielding a relatively low overall load factor.
Underutilized transport capacity means more pollution and road damage per unit of
transport service delivered; hence capacity utilization itself is an important indicator
of sustainable transport.
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