92 ■ CITIES AND CLIMATE CHANGE
suffi cient and that many slum dwellers are able just to walk to work. Some have
argued that slum dwellers’ lack of motorized mobility and inclination toward
walking would constitute an advantage in terms of GHG emissions and should
be emulated by higher-income groups. Th is argument is a cruel joke on the
poor because their lack of mobility condemns them to live in large cities with
all its costs but none of its benefi ts. Th e lack of mobility in many slums and
in some badly located government housing projects constitutes a poverty trap
rather than an advantage to be emulated in the future (Gauteng in South Africa
being a case in point).
Although walking and cycling do constitute an indispensable transport
mode in large cities, people using these modes should do it by choice, not
because they are forced to do so by lack of access or aff ordability of other means
of transport. Because mobility is a necessity for economic survival in large cit-
ies, a reduction of GHGs should not be made by reducing mobility and cer-
tainly not by preventing an increase in mobility for the poor. Th e reduction of
the number of passenger kilometers traveled (PKmT) should not be targeted
for reduction to reduce GHG emissions. To the contrary, because of the lack of
mobility of a large number of poor people living in large cities, PKmT should
increase in the future. Various alternative solutions to decrease GHG emissions
while increasing PKmT are discussed.
Identifying Key Parameters in Urban Transport GHG Emission
Sources
GHG emissions from transport are produced by trips that can be divided into
three broad categories:
- Commuting trips
- Noncommuting trips
- Freight
Commuting trips are the trips taken to go from residence to work and back. In
most low-income cities, commuting trips constitute the majority of trips using
a motorized vehicle (with exceptions in some East Asian cities where nonmo-
torized trips still constitute a large number of commuting trips). Noncommut-
ing trips are trips whose purpose is other than going to work, for instance, trips
to schools, to shops, or to visit family or other personal reasons.
In high-income countries, commuting trips constitute only a fraction of total
trips. For instance, in the United States, commuting trips represented 40 percent
of all motorized trips in 1956; in 2005, they represented only slightly less than
20 percent of all motorized trips (Pisarski 2006). In low-income cities, most of