Geographical Paradoxes behind Urban Transport Problems
Motorization leads to three major countervailing forces (paradoxes):
The above figure illustrates the negative impacts on three simplified
urban settings of specialization, agglomeration and road imprint:
- Spatial specialization. The differentiation between land
uses is a generator of movements as people and freight move from
several origins and destinations. Thus, the more complex and specialized
the land use patterns, the more complex their associated movements
will be. Also, efficient and affordable transportation will enhance
the segregation of land uses and favor a growth of traffic.
- Spatial agglomeration. Since cities benefit from agglomeration
economies, activities located nearby each-others benefit from increased
interactions, which also decrease transport costs. However, the
agglomeration of movements in a limited area creates congestion,
which increases the costs of movements. This can reach a point where
the advantages of agglomeration are overthrown by the costs of congestion.
- Spatial imprint. The main goal of transportation is obviously
to overcome the friction of distance by providing a level of mobility.
However, transportation, like any urban function, consumes space
and thus has a spatial imprint. While space is the rarest (and consequently
the most valuable) in urban areas, transportation requirements are
at their highest levels. A compromise is thus sought between the
availability of space devoted to transportation and the desired
level of mobility.
- A North American suburb tends to have a high level of
specialization as most land uses are monofunctional. The level of
agglomeration is low, which implies that many streets are underused
and that distances between activities are on average significant.
The spatial imprint of transportation is high, especially compared
to the level of density, implying a high level of automobile dependency.
- The residential section of an European city is fairly
multifunctional with different economic functions sharing the same
space. Typically, residential and locally oriented commercial functions
are closely integrated. This is linked with a good level of agglomeration,
enabling a significant share of movements to occur locally either
by walking or by public transit. This characteristic implies a lower
spatial imprint of transportation as movements occur on more spatially
efficient urban transportation modes.
- Residential areas in a Japanese city share several commonalities
with European cities in terms of the level of specialization. However,
higher levels of agglomeration tend to imply higher levels of congestion
which is reinforced by lower spatial imprint of urban transportation.