| Land Use and Growth Management |
| Guidance for Land Use Impacts of Transportation |
| By Samuel N. Seskin, Portland, Oregon, 1-503-274-9554, seskin@pbworld.com
|
| PB prepared a guidebook
that provides state departments of transportation and metropolitan
planning organizations with practical suggestions about how to carry
out land use analyses in conjunction with transportation planning.
A summary of the guidebook's contents is presented in this article. |
|
Analysts usually have a basic understanding of transportation and
land use relationships, yet often find it difficult to predict the
outcomes of specific plans or policies. The main reason for this uncertainty
is the complex, dynamic nature of the urban development process. More
specifically, our ability to predict outcomes from a transportation
or land use policy change is affected by local conditions, the incremental
long-term nature of land use change, random events and the flexibility
of travelers' responses.
Despite these difficulties, long-range planning must take place, and
transportation/land use impacts must be evaluated within the planning
process to the extent possible. Tables 1 to 3 summarize the state
of knowledge about the impacts of transportation investments and policy
on land use and vice-versa.
Tables 1 and 2 indicate the relative elasticity of land use impacts
from various types of highway and transit investments and policies,
respectively. In other words, the tables provide a measure of the
degree to which land use impacts will occur. When an action is labeled
as having "high" land use elasticity, the implication is
that the results are high in relation to the other options, not that
the changes are necessarily large. Similarly, Table 3 indicates the
relative elasticity of transportation impacts from land use changes.
In reading Tables 1 and 2, it is important to remember that highway
and transit improvements may have different spatial impacts. Highway
impacts tend to be more diffused and, thus, may be harder to measure
than transit impacts. Highways are multimodal; they serve individual
travelers, public transit, and goods movement, therefore changes in
highway accessibility directly affect all aspects of economic activity.
Under favorable conditions, then, highways can have major impacts
on the distribution of development in metropolitan areas. Because
transit serves only passengers, its land use effects are likely to
more localized and, thus, more definable than highway impacts.
Tools and Techniques
Metropolitan planning organizations (MPOs) and state departments of
transportation (DOTs) can use a variety of tools for land use forecasts
and land use impact assessment depending upon the questions they have
been asked to answer, their size, and their interests in advancing
the practice. Eight basic types of analytical procedures or tools
currently available and in use are identified in the guidebook:
- Comprehensive plans and other land use regulations
- Qualitative methods that tap expert knowledge
- Allocation rules for assigning population
and jobs to zones
- Decision rules
- Statistical methods
- Geographic information systems
- Regional economic models
- Formal land use models.
Comprehensive Plans and Other Land Use Regulations. It is important
to understand the land use regulations that influence where and what
type of development can occur. Current practice tends to rely too
heavily on public policy as the primary shaper of urban form, however.
For political reasons, many regions produce "plancasts"
that assume development will occur where land use policies and regulations
direct that growth. When using comprehensive plans in forecasting
and impact assessment, it is important to evaluate realistically the
effectiveness of these tools in shaping growth and to consider how
the land market might produce different outcomes from those described
in policy.
Table 1: Summary of Land Use Impacts of Highway Investments
and Policies
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Table 2: Summary of Land Use Impacts of Transit Investments
and Policies
 |
Table 3: Summary of Impacts of Land Use Policies on Travel
Demand
 |
Qualitative Methods that Tap Expert Knowledge. MPOs and DOTs
use a variety of qualitative methods to understand the complexity
of urban development. These tools can be used as the primary method
of analysis or in conjunction with other tools. Panels of experts,
Delphi's, interviews, surveys, and case studies are qualitative techniques
that rely on the knowledge and skills of one or more experts to determine
where growth is likely to occur. These methods can combine understanding
of the theory of urban development, empirical knowledge of transportation
and land use interactions, and understanding of local situations.
[Ed note: See also "An
Application of the Delphi Technique for Highway Corridor Land Use
Impact Analysis" by Katherine Still and "Highway
99W Trip Budge Model" by Lawrence Conrad.]
Qualitative methods are not substitutes for data collection. They
should be based on a sound understanding of existing conditions and
trends, but this information is often analyzed by experts without
statistical techniques or models to estimate what the future will
hold. The results of qualitative approaches depend upon the breadth
and depth of knowledge of the experts involved in the process.
Allocation Rules for Assigning Population and Jobs to Zones.
Allocation rules use simple trend extrapolations (e.g., fast growing
areas will continue to grow rapidly) or simple measures of accessibility
and other attractiveness factors to allocate expected growth to different
zones. They are easy to use and do not require extensive data.
Allocation rules work best in typical situations and for widespread
activities like retailing and residential development. They must be
supplemented with other methods, such as qualitative analysis, to
decide how to handle issues including location of large employers,
changes in household, business locational preferences, and other factors
that might cause future development to differ from past patterns.
All assumptions must be explicit.
Decision Rules.
Many land use forecasting or impact assessments require some simple
decision rules that quantify certain relationships between transportation
and land use. These rules are based on empirical evidence from the
region or from other locations with similar projects. Decision rules
are often needed because the process of urban development is too complex
to analyze in its full detail. They are typically used in conjunction
with another process, such as geographic information systems (GIS)
analysis of developable land. Especially when using decision rules
from another location, the context in where they were developed must
be carefully compared with the study area to determine whether there
are any critical differences in these places that might invalidate
the use of the rule.
Statistical Methods. Multiple
linear regression and discrete choice models are two statistical methods
for evaluating the relative roles of multiple factors in shaping land
use patterns. Because they consider the effects of multiple variables,
they can represent more of the complexity of urban systems than simple
allocation or decision rules, provided the appropriate variables are
included in the analysis. These methods require considerable technical
skills and large data sets to provide accurate results. Like other
methods that rely on recent local data, they assume that past trends
will continue into the future. These models provide information about
what happens "on average."
Geographic Information
Systems. Increasingly, MPOs and DOTs are using GIS to manage,
analyze, and map geographic relationships. GIS can be used in conjunction
with any of the other tools to help understand trends and development
opportunities and to sort out the complex behavior and interactions
in the land market. While the cost and difficulties of using GIS have
been declining as new PC-based systems have been developed, considerable
staff time is required to set up and maintain the databases for an
effective GIS.
Regional Economic Models. Regional
economic models simulate an area's economy and are useful for estimating
regional population and employment growth totals that are needed as
input to other forecasting processes. They can also be used in inter-metropolitan
impact assessments to assign growth to individual counties for large
geographic scale projects. Some models predict only job growth; others
include both job and population growth. A number of models are commercially
available and others have been developed for particular regions by
MPOs, DOTs and other state agencies. It is important to understand
the assumptions of the regional economic model when interpreting the
output.
Formal Land Use Models. The principal formal
model systems in use or available today include DRAM/EMPAL, MEPLAN,
TRANUS, METROSIM, HLFM II+, LUTRIM, CUF. While this class of analytic
techniques is suited to large scale analyses for which few other tools
exist, users of formal land use models are concerned about how difficult
they are to use; their high costs in time, data and consulting needs;
the accuracy of the results; the lack of integration with transportation
models; and insufficient documentation.
DRAM/EMPAL and HLFM II+ are based on Lowry gravity models that assume
that accessibility is the key concept in location choice. They do
not adequately represent other factors that influence the location
choices of households and firms.
Some of the models, such as CUF and TRANUS, have been designed for
ease of policy analysis. The experience with these models is limited,
however, with the first full-scale applications of these models in
the U.S. currently underway.
A Framework
for Understanding the Land Market
People seek housing that satisfies their needs and preferences and
fits within their budgets. Accessibility is only one of many factors
that are considered when these choices regarding housing are being
made. Because the majority of trips are made for non-work reasons,
people consider access to stores, services, friends, and other destinations
besides work when choosing housing. Many are more concerned about
affordability than with access to jobs, provided they are not too
distant from the current jobs of household members. For those who
have a large set of affordable choices, other factors such as school
quality, neighborhood amenities, and the type of people living in
the community can play a decisive role in their final choices.
Firms seek locations where they can make a profit. Different types
of firms place different emphasis on access to workers, customers,
suppliers, and others. Like households, firms must consider multiple
factors including accessibility and affordability in making location
decisions. The final site selection may hinge on factors such as differences
in local tax rates, the cost and availability of services, and the
prestige of the location.
Developers balance the needs and preferences of potential customers
with the costs of developing in different locations when deciding
where and what to build. They consider both the factors that influence
household and locational choices, such as preferred locations and
site characteristics, and the costs and land supply limitations, if
any, due to governmental policies.
Government policies influence the supply of land available for development
and affect the cost of development. The supply of land available for
different types of development is constrained by zoning, environmental
regulations, and the provision of water, sewer, and other infrastructure.
The cost of development can be lowered with economic development incentives,
or it can increase with the cost or uncertainty of obtaining permits,
of infrastructure extensions, or of meeting requirements for parking
or design standards.
These players interact in a market where the price for land acts as
a sorting mechanism to determine the type and location of development.
People, businesses, and developers are willing to pay for land up
to the amount they anticipate they will receive in future benefits.
Some stand to benefit from certain locations more than others and
will outbid all others for these desirable sites.
Conducting
Land Use Analysis
Table 4: Comparison of Steps in Base Case Forecasts and
Impact or Policy Assessments
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Table 5: Summary of Analytical Tools and Their Relationship
to the Behavioral Framework
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The steps that analysts should follow when seeking to conduct base
case land use forecasts and land use impact or policy impact assessments
are outlined in Table 4. Both tasks require:
- Understanding the existing transportation
and land development patterns
- Making assumptions about the policy framework
that will guide the process
- Estimating the amount of growth expected
during the planning period in the study area
- Inventorying land that might be developed
and any physical and regulatory constraints on that development
- Assigning the expected growth in households and jobs to specific
locations.
The key difference between the processes is that an impact or policy
assessment requires estimates of the ways that accessibility and travel
behavior will change because of the investments or policy changes.
In addition, an impact or policy assessment requires a comparison
not only with existing conditions, but with the quantity, type, and
location of future growth that would occur without the projects or
policies.
The behavioral framework can be incorporated into these steps using
the land use analysis tools in Table 5. Impact or policy assessments
also require the use of travel demand models in Step 3 to provide
estimates of the changes in transportation demand that transportation
investments or policies will produce.
Major
Lessons From the Guidebook
Experience in the application of the above tools and techniques for
land use forecasting and impact analysis suggests the following lessons
for analysts.
Think through the process of development.
How do developers decide what and where to build? Where do people
of various types want to live? Where do firms want to locate? How
do public policies restrict or expand the choices available?
Improve understanding of both the general process of development
and the particular players in your region. General patterns can
tell a lot. People base their location choices on the same factors
in most parts of the country. Developers of national franchises consider
a standard set of criteria. Regions do differ, however, in the types
of developers who work there, the nature of households and firms,
and the role of public policies. It is equally important to improve
understanding of these differences from general patterns.
Incrementally improve the land use forecasting and impact assessment
process. Develop a plan to acquire over time the data and skills
needed to better understand and analyze the process of development.
Develop measures of accessibility that reflect the complex
decision-making of households and firms. Household members may
be considering both the current and future job locations, access to
services such as daycare facilities, the convenience of shopping,
the location of cultural and recreational opportunities, and the homes
of their friends and relatives when deciding where to locate. Likewise,
consider the different accessibility needs of retailing, offices and
industry.
Recognize that other factors may be just as
important as, or even more important than, accessibility. Most
households and firms have budgets that limit their choices. If there
is a wide variety of choices within their budgets, households and
firms consider a wide variety of factors before making final locational
choices.
Understand the potential and limitations of public
policies for shaping the pattern of development. Zoning land for
a particular type of development does not guarantee that that type
of development will occur; neither do economic development incentives.
When these polices work in concert with market forces, however, they
can shape development.
Realistically evaluate local governments' approaches to public policies.
Does development follow the designations in zoning or are changes
readily made? Do local governments make it easy or difficult for development
to occur through their permitting process, costs charged for fees
and permits, and incentives offered?
Recognize that infill
and redevelopment can accommodate a significant share of growth. Forecasts
that assume all development occurs on vacant land will overestimate
the demand for vacant land.
Involve both technical and
policy people in the process. Every land use forecast and impact
assessment includes making assumptions about the policies that will
affect land uses. Every process uses analytical tools with inherent
assumptions. Both policy makers and technical professionals should
be involved in making these assumptions explicit. Agreement on the
assumptions should produce forecasts that are more credible.
Choose analytic techniques and tools that suit the situation. For
example, formal land use models require the most data and time, and
they generally suit analyses at a larger geographic scale. Qualitative
methods suit smaller sites and projects, though they may also be applied
to larger area. |
|
| Sam Seskin, a Principal Professional Associate
in PB's Portland, Oregon, office, is co-author of the two volume report,
"Transit and Urban Form" (1995, National Academy Press)
and of "The Costs of Sprawl, Revisited" (1999, National
Academy Press) He has written a guidebook on the land use impacts
of transportation investments, and is working on two others for the
National Academy, "Benefits and Costs of Transit" and "Benefits
and Costs of Highways." Sam was the Consultant Project Manager
for the award winning LUTRAQ Project ("Making the Land Use/Transportation/Air
quality Connection) for 1000 Friends of Oregon. |
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