Urban Growth Modeling Urban Growth Modeling ApproachesApproaches

Discussion 1Discussion 1

OverviewOverview

Planning Theory Meets ModelingPlanning Theory Meets Modeling

UrbanSim as an example of complex UrbanSim as an example of complex landuse/transportation modelinglanduse/transportation modeling

Theory Revisited: which capabilities Theory Revisited: which capabilities under which circumstances?under which circumstances?

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

Assumptions & ForecastsAssumptions & Forecasts

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 criterionAccuracy 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

ComplicatednessComplicatedness

KlostermanKlosterman ““(M)odels will only be useful in a policy (M)odels will only be useful in a policy

context if policy makers and the public context if policy makers and the public understand and trust them.” understand and trust them.”

““As a result, planners should attempt to As a result, planners should attempt to develop models that are as simple—develop models that are as simple—rather than as complex—as possible.”rather than as complex—as possible.”

Waddell / UrbanSimWaddell / UrbanSim

MotivationMotivation ““Metropolitan areas have come under intense Metropolitan areas have come under intense

pressure to respond to federal mandates to link pressure to respond to federal mandates to link planning of land use, transportation, and planning of land use, transportation, and environmental quality”environmental quality”

““Requirements for improved and better Requirements for improved and better integrated land use and transportation models integrated land use and transportation models have emerged not only in response to this have emerged not only in response to this federal legislation, but also from state growth federal legislation, but also from state growth management programs that promote closer management programs that promote closer linkage of land use and transportation linkage of land use and transportation planning”planning”

UrbanSim Data OrganizationUrbanSim Data Organization

UrbanSim Model StructureUrbanSim Model Structure

UrbanSim Interface ExampleUrbanSim Interface Example

Concluding Discussion Concluding Discussion PointsPoints

Is Simplicity in the eye of the beholder?Is Simplicity in the eye of the beholder? If it is important, shouldn’t it be measured and tested, not If it is important, shouldn’t it be measured and tested, not

simply asserted?simply asserted? To what degree can or should planning model complexity To what degree can or should planning model complexity

be “hidden” from usersbe “hidden” from users How important is it that transportation modeling be How important is it that transportation modeling be

integrated with land use?integrated with land use? How can planning processes be organized to take How can planning processes be organized to take

advantage of models? advantage of models? Who provides modeling assumptions? (what if not supported Who provides modeling assumptions? (what if not supported

by empirical evidence?)by empirical evidence?) Must modeling be supported by a technical team, or is “hand’s Must modeling be supported by a technical team, or is “hand’s

on” modeling beneficial in and of itself? on” modeling beneficial in and of itself? If technical modeling support is required close contact with end If technical modeling support is required close contact with end

users? users?