| Land Use and Growth Management |
| An Application of the Delphi Technique for
Highway Corridor Land Use Impact Analysis |
| By Katherine Gray Still, Portland, Oregon 1-503-274-7219,
still@pbworld.com |
| Planners are continually
seeking better ways to determine the land use impacts of transportation
infrastructure projects. The Delphi is an excellent option in a variety
of situations. |
|
Over the last ten years, metropolitan planning organizations (MPOs)
and state Departments of Transportation (DOTs) have faced new federal
requirements regarding the land use impacts of transportation infrastructure
investments in the U.S. Most notably are those mandated by:
- The Clean Air Act Amendments (CAAA) introduced
in 1990
- The Intermodal Surface Transportation Efficiency Act (ISTEA)
introduced in 1991 and later reauthorized in 1998 as the Transportation
Equity Act for the 21st Century (TEA-21).
These policies have significantly increased the level of land use/
transportation interaction analysis that MPOs and DOTs must carry
out to complete major investments studies and environmental impact
statements.
This article describes a successful application of the Delphi technique
to assess the land use impacts of several proposed highway improvements,
including the construction of a new interchange, along Interstate
5 in Clark County, Washington, for Washington State Department of
Transportation (WSDOT).
Overview
of the Delphi Technique
Analysts usually have a basic understanding of land use and transportation
relationships, but the complex and dynamic nature of the interaction
challenges their efforts to create better methods of analysis. The
Delphi technique provides a more rigorous analysis than case studies
or interviews without the large time and data requirements of a formal
modeling process.
The highly structured Delphi is a technique in which selected experts
provide their assessment of likely future events or outcomes by responding
to several rounds of questions. First developed by the Rand Corporation
in the 1950s for use in defense applications, it has been used in
a wide variety of applications since the 1960s. For example, the city
of Longview, Texas, used a Delphi process to allocate future population
and employment growth as part of its two most recent metropolitan
transportation plan updates, both of which were prepared by PB.
For transportation-related projects, Delphi participants are generally
selected according to their expertise in the field being analyzed
and to represent a variety of disciplines (i.e., developers, planners,
public officials, academics, brokers and consultants). Rounds of questioning
are conducted by a moderator who tallies and summarizes the results
of each round, then provides these results to the participants for
the next iteration. The participants remain anonymous during the analysis
period so that no one can influence his or her peers and dominate
the analysis. The Delphi is considered complete when the responses
to a round of questioning no longer change markedly. Most Delphis
involve three to four rounds.
WSDOT
I-5/I-205 North Corridor Study
WSDOT's I-5/I-205 north corridor runs through northern Clark County
in the southwestern corner of Washington State. The county, where
the city of Vancouver is located just across the Columbia River from
Portland, Oregon, has had very high rates of population growth over
the last 20 years.
WSDOT elected to use a Delphi process when preparing its I-5/I-205
North Corridor Study in order to understand better the possible land
use and economic development impacts of several proposed highway projects
along the corridor. A key issue was a proposed new interchange on
I-5, just three miles north of Vancouver's urban growth area (UGA).
An interchange has long been sought by the growing community of Battle
Ground (1998 population of 8,460), six miles to the east of I-5. Others
have argued that the interchange could exert strong pressure to expand
the current UGAs of Battle Ground and/or Vancouver and, at a minimum,
induce development pressure on rural lands around the designated interchange
location, but such development is contrary to the requirements of
Washington's Growth Management Act (GMA), adopted in 1990.
The WSDOT Delphi had the following characteristics:
- It employed a small panel, whose six members were drawn from
both within and outside the state.
- It dealt entirely with a qualitative assessment
of land use and economic impacts to a relatively small geographic
area, unlike many previous applications, which involved a quantitative
forecast of population and employment growth.
- The process was capped off with a two-day
public forum, during which the panelists met one another, discussed
their findings and presented them to the public.
- In keeping with time and budget constraints the number of rounds
of question and response was limited to two, which was considered
sufficient to reap the benefits of an iterative process.
Preparation for the Delphi included development of a briefing book
with general policy, demographic and economic information in the form
of text, data and more than 35 maps. The panel relied on this information
when analyzing the issues.
The most challenging aspect of the process was carrying out an entirely
qualitative Delphi. Most Delphi applications use questions that yield
a quantifiable response, either:
- The result of a question that asks for a number in reply (e.g.,
"give the employment and population totals by traffic analysis
zone for City X")
- More qualitative-type questions that prompt the panelist to
give a ranked response (e.g., "X outcome is (1) very likely
to occur, (2) somewhat likely," and so on).
The WSDOT Delphi asked open-ended questions such as: "What type
of development is likely to occur over the next 20 years, with and
without the 'catalyst' highway projects?" Thus, the burden of
determining consensus rested upon the ability of the panelists to
respond directly to the point and, importantly, on the moderator to
be able to interpret the intent of their responses. As a safeguard,
the panelists were given the opportunity to verify the interpretation
of their replies.
Despite the challenges inherent to a qualitative Delphi, the open-ended
nature of the questions met WSDOT's desire to take full advantage
of the experts' knowledge rather than limiting responses to pre-determined
options (i.e., through rankings). This was particularly the case in
dealing with the complex issue of the proposed interchange's impacts.
Lessons Learned
Three themes illustrate the lessons learned from this application
of the Delphi process.
Special Challenge of Qualitative
Approach. The challenge in using qualitative questions is to focus
the panelists' responses on the specific points of interest so their
responses will be as clear and direct as possible for the moderators.
One way to gain greater clarity of responses would be to pre-test
the materials and questions with a sample group (peers, for example)
to ensure that the answers fall within an expected range of answers
regardless of participant.
Panel of Outsiders and Locals.
The project team felt that combining outside expertise with local
knowledge contributed substantially to the depth of the analysis.
Aiming for a panel of half local, half non-local members provided
an excellent balance and utilized the strengths of both groups. The
local panelists benefited from the perspective brought by outsiders,
who provided an additional benefit of decreasing the risk that the
panelists might bias the results due to local interests. The non-local
panelists were able to take advantage of the location-specific knowledge
provided by the local members.
Effect of the Public Forum.
While quite outside the normal workings of a Delphi process, the public
forum enhanced the public's awareness of transportation planning and
the consideration of land use impacts-two important steps in gaining
public consensus for transportation projects.
Using
Delphi Results
WSDOT's confidence in the credibility of its Delphi has led the agency
to circulate and publicize the results widely among the cities that
were the subject of the analysis, committee members, and others involved
in the decision-making process. The process has also been well received
by the community. The panelists found the process "refreshing"
and expressed enthusiasm for future applications of its kind. In other
words, all participants left the experience feeling that the process
and its results were credible and legitimate. This is a great benefit
for agencies that continue to seek ways to open up the process of
transportation planning, as well as to carry out rigorous and efficient
analyses of complex land use-transportation issues. |
|
| Katherine Gray Still has been with PB for just
over 2-1/2 years. Working in the Portland office, her experience includes
research and analysis of the impacts of transportation projects on
land use and economic development, including the full cost of transportation
and congestion pricing. She has a Master of Planning degree from the
Hubert H. Humphrey Institute of Public Affairs, University of Minnesota
and a B.A. in economics, magna cum laude, from the University of Colorado
at Boulder. |
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