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CAPABILITIES
FOR MODELING URBAN GROWTH AND ITS IMPACTS SUSTAINABLE COMMUNITIES CONSORTIUM UNIVERSITY OF CALIFORNIA, DAVIS December 15, 1997
The
Role of Models The following models may be used for: 1. Analysis of past and present spatial patterns of
phenomena (with maps and descriptive statistics),
2. Prediction of the most likely future patterns of these
conditions, and Analysis and prediction can
help to identify common ground among user groups, as they come to
understand and accept current problems and future likely problems.
Regarding prescription, we believe our role to not be one of advocacy of
particular viewpoints, but rather to be one of clarifying value choices,
especially the values that are traded off when one selects any particular
policy set. In order for models to help us to understand these tradeoffs,
the models must be complex enough to represent a great variety of social,
economic, and environmental phenomena.
In addition to being
"truth-telling" devices, models also help us ask the right
questions. In this heuristic role, models allow us to learn together about
the urban region and to test prescriptive concepts. Models can greatly
facilitate bargaining, by bringing all interest groups into the planning
process and allowing the quick testing of the ideas of all participants.
Models that run in a few minutes or less on PCs,
can be used in real-time analyses in meetings, creating a detailed
real-time discourse. Models can be useful in all
these roles, because they are systematic assemblages of our assumptions
about how the world works. They provide a consistent framework for our
discussions and analyses. Models do not provide answers, they just
illustrate various points of view. Since they employ graphical outputs,
models can greatly help get interest groups to meet together and bargain,
because of the evocative methods of analysis and portrayal used. Models generally contain errors of at least 1% per year of projection, much of this caused by input error (aggregate population forecasts input to start the model). In long-range forecasting, we ignore the input error (we assume under- or over-projection of population just means we are projecting for a nearer or farther year), and concentrate on the differences across alternative futures (their rankings). Typical planning is for 20-year time horizons. We will perform 50-year scenarios, to project growth impacts more clearly. |
TOP | 1. TRANUS, a state-of-the-art integrated urban model. Tranus is a spatial interaction model that represents
land markets and travel markets with supply and demand functions (of the
discrete choice, random utility type). It represents several classes of
households, employment, land uses, and trips. It equilibrates a land use
model with a travel model, to represent the interactions of these systems,
over time. We have calibrated Tranus on Sacramento region data (four
counties) and have run it on four policy scenarios (Trend scenario, New
HOV lanes, HOV lanes plus two outer beltways, and Transit expansion with
parking charges in the downtown). Tranus is difficult to calibrate and
requires considerable data for calibration.Tranus, however, is quite
complex. For example, it represents the bid-rent density function, where
demand for land in central locations drives building density and land
prices up. It can represent demolition and rebuilding. Tranus gives a
consumer welfare measure, traveler surplus (net economic benefits to
travelers, by household income class). Because of its statistical
complexity, this model only operates on large zones, 58 in our application
to the Sacramento region. So, we use our version of the Landis GIS model
as a second-stage land use allocator (see 2., below). Tranus could be
applied to any other large metropolitan region in the state, at
substantial cost ($100,000-200,000). It could also be applied at the state
level, as it can represent inter-regional flows of goods and people.
Tranus is currently being applied to the State of Oregon. Outputs include:
trips by mode, vehicle-miles of travel, vehicle speeds, acres of each land
use by zone, wages, land rents, travel costs by household income class,
and traveler net benefits. The travel outputs from Tranus can be fed into
DTIM2 or BURDEN with EMFAC7F, the official California models, to get
vehicular emissions. We have developed a crude floorspace consumption
model from Tranus land consumption data. From the floorspace and travel
consumption projections, we can calculate energy use and greenhouse gas
emissions from vehicles and buildings.
2. California Urban Futures Model. John Landis (UC Berkeley) has developed a rule-based land allocation model that runs in a GIS (geographic information system). This model is less sophisticated than Tranus, but access to services and roads is represented, statically. We have altered the model considerably, to take account of vacant land, new urban areas, and other complexities. In our version, several categories of urban land use are represented and densities can be changed. It is appropriate to use on simple (monocentric) urban regions. We have used our version of this model for two years now with reasonable results for the four-county Sacramento region. We use it as a second-stage land allocation model, to disaggregate the land use projections from the Tranus model, in each of the 58 zones. We are currently rewriting the programs in ArcView3.0 (with Spatial Analyst and Avenue), so it will run easily on PCs. We have recently acquired a detailed urban coverage for 1992 and will soon receive the SACOG digital generalized general plan coverage, both for the six-county region. We are moving the model over to 25m grid cells, which will allow much greater spatial realism. The existing urban layer will permit much more accurate allocations than we have done to date. By itself, this model allows the testing of general plan controls, environmental constraints, new roads, and changes in service districts. This model can be applied to any urban county or group of counties, for which we have GIS coverages. Outputs include: acres of each land use, acres of prime ag land urbanized, acres of each habitat type urbanized, and other GIS combinations. Application to a county with all necessary data layers will be very inexpensive ($10,000), involving only the customization of some user screens and Avenue commands. |
TOP | We cooperate with the
Information Center on the Environment (ICE), which is located at UC Davis.
ICE is a repository for natural resources datasets for California and has
the most complete set of GIS data available. For example, ICE makes
available the GAP vegetation
layer, which represents plant and animal communities. ICE also has a
detailed dataset for riparian habitats in the state.
Other datasets include the Natural Heritage database (NDDB), the
Holland classes, CalFlora, and the WHR models. In addition, this group has
basic datasets, such as the TIGER line files, digital elevation data
(DEM), surface water bodies, and county and watershed boundaries. ICE
staff have strong capabilities in GIS, including theme draping on 3-D
shaded relief maps, jpeg animations of land cover type changes over time,
and AML and Avenue programming. ICE also has developed an interactive habitat rating model, CARES. This model has interactive (user) screens that permit the user to change the variable weights in the additive function for habitat quality. One can also change the functional form of the equation. ICE recently improved their webpage to include click and zoom capabilities on map images for the whole state. This page is linked to LUPIN and CERES. |
TOP | Community design research
integrates quality of place and livability criteria with other SCC
research. Movement within
communities; relationships between working, living, and leisure
environments; managing growth; enhancing the quality of community life and
increasing sense of place; maintaining productive agricultural land and
healthy ecosystems, improving air and water quality; offering a full range
of employment opportunities as well as providing a variety of affordable
housing types, are a few of the issues that design affects.
Design is a cognitive, problem solving activity that integrates
these issues, creating the relationships, structure, and forms that can
have significant social, economic, and environmental impacts.
Implementing polices and creating real, functional, sustainable
systems and places is the role of community design.
Two major movements,
livable communities and sustainable development, are influencing
contemporary urban design. While definitions are often inclusive,
livability can be thought of as a qualitative goal of making urban places
as humanistic and rewarding as possible.
Principles include pedestrian-scaled environments, safe private and
public places, cultural and
historic preservation, diversity in community living at all economic
scales, adequate housing, and others.
Sustainability can be more functional and quantitative than the
qualitative aspects of livability. Sustainable
communities seek a balance between inputs and outputs.
They are designed to be resource efficient.
They enhance living systems; have strong economies that do not
degrade the environment; promote clean air and habitat protection; and
seek lower life-cycle costs. And
most importantly, they plan for current and long-term successful
operations. Our Sacramento study is
investigating the realm where livability and sustainability are mutually
supportive. Multiple urban
conditions are being investigated, including revitalization and
intensification of underutilized parcels, commercial strips, older
shopping malls, and central districts.
Development of single-family housing alternatives that increase
density and affordability are being explored.
Guidelines to increase urban livability through the design of
effective public and private open spaces are being studied.
The city in the context of permanently protected elements of the
Central Valley landscape, including agriculture, habitats, and other open
spaces are being explored. Current design theories,
research, and experiences are informing the community design studies.
The Consortium is affiliated with Community Design & Planning
Services, an applied research and community design unit at UC Davis.
In the past 3 years the unit has conducted 22 research and
participatory studies in communities and has developed planning and design
recommendations for 60 community development projects.
The work of the New Urbanists, such as Peter Calthorpe, Andres
Duany, Elizabeth Plater-Zyberk, and others are particlulary valuable for
defining issues and suggesting design patterns.
Experiences in other regions and countries is also factored into
the work. What distinguishes the SCC community design studies from previous efforts is the degree to which quantitative and qualitative data will inform design. The regional modeling assessments will test alternatives and quantify the effects of sustainable planning and design strategies. Sacramento Valley residents will also review and inform the studies, providing information that will make the design research recommendations appropriate to and sought after by those who live in the region. | TOP | |