Urban Growth Modeling
Approaches
Discussion 1
Overview
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Planning Theory Meets Modeling
UrbanSim as an example of complex
landuse/transportation modeling
Theory Revisited: which capabilities under
which circumstances?
Assumptions & Forecasts
The core assumptions that underlie a forecast … play a much
larger role in determining the forecast outcomes than the
sophistication of the tools used to prepare them
Planning models should explicitly state their underlying assumptions
concerning future trends and alternative policy choices.
These assumptions should be easily modified and the effects of
alternative assumptions and policy choices should be easily
identified
Accuracy as a criterion
…(A)ccuracy cannot be the proper criterion for evaluating
forecasts.
Instead, planning forecasts should be evaluated with respect
to their ability to inform the policymaking process, facilitate
community understanding, and prepare the public to deal with
an uncertain future
Complicatedness
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Klosterman
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“(M)odels will only be useful in a policy
context if policy makers and the public
understand and trust them.”
“As a result, planners should attempt to
develop models that are as simple—rather
than as complex—as possible.”
Waddell / UrbanSim
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Motivation
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“Metropolitan areas have come under intense
pressure to respond to federal mandates to link
planning of land use, transportation, and
environmental quality”
“Requirements for improved and better integrated
land use and transportation models have emerged not
only in response to this federal legislation, but also
from state growth management programs that
promote closer linkage of land use and transportation
planning”
UrbanSim Data Organization
UrbanSim Model Structure
UrbanSim Interface Example
Concluding Discussion Points
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Is Simplicity in the eye of the beholder?
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If it is important, shouldn’t it be measured and tested, not simply
asserted?
To what degree can or should planning model complexity be
“hidden” from users
How important is it that transportation modeling be integrated with
land use?
How can planning processes be organized to take advantage of
models?
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Who provides modeling assumptions? (what if not supported by
empirical evidence?)
Must modeling be supported by a technical team, or is “hand’s on”
modeling beneficial in and of itself?
If technical modeling support is required close contact with end users?