ECONOMIC FORECASTING REVIEW - Parsons Brinckerhoff

Vol. 3 • Issue 2
Estimating Impacts of Transportation Capacity Expansion
Qualitative analysis
Through a rigorous process of data
collection regarding ancillary factors
that govern development (other than
transportation network improvements)
and through interviews with local
planning professionals and real estate
experts, a reasonable theory can be
formed regarding developmental
impacts of the project. Some of the key
questions to address would be:
Changes in network performance: What
does the transportation project do to
highway performance (accessibility,
travel-time, volume, mobility, and
safety) that is different from what that
performance would be without it?
Change in accessibility is one of the
key determinants of the magnitude of
development attributable to the project.
Expected growth: How do those changes
in travel performance influence factors
that help shape development patterns
such as population and employment
growth? Does the project have potential
to spur new development or would it
just redistribute expected growth?
Public policy: What policies exist on the
books to offer resistance to potential
land use change?
Answers to these and similar questions
can be sought through a process of
interviews, where various stakeholders
are asked to provide qualitative inputs
while also classifying outcomes in
ranges (such as low, medium, high for
travel time benefits, land supply, etc.)
These ranges can then be mapped to
probability of induced development
through use of experienced judgment.
For instance, if the project brings about
“high” or significant improvement
in the transportation network
performance, measured through
greater time savings and/or through a
better or faster connection to a poorly
connected rural or suburban area, the
potential for induced development
may be high. However, a project which
results in “low” or “moderate” travel
time savings may have lesser potential
to encourage induced development
as it may not give enough incentive
to deviate from planned development
patterns.
Quantitative analysis
As argued above, growth invariably
spurs travel. Hence one indicator of the
magnitude of induced development
is increment of travel. Cervero’s (2003)
Longer-Term Path Model captures the
relationship between transportation
supply, induced development, and
induced travel.
In order to understand induced travel
it is essential to look at transportation
through the “supply” and “demand”
lens of classical economics. In
transportation, typically the supplyside
comprises the transportation
infrastructure and the quantity of
supply is the available capacity on
the existing modes, such as the road
network capacity during peak periods
of travel. Travel demand on the other
hand is the demand (existing or latent)
for people to travel using a particular
mode during a specific time period.
The equilibrium-governing price is a
composite “generalized cost,” which
is a sum total of the time cost of travel
and the out-of-pocket expenses such
as fuel and vehicle maintenance
Land supply: What is the land supply
situation in the study region? The more
limited the supply, the more likely
that improved access will contribute
to pressure for zoning changes in the
study area.
SUPPLY:
Lane Mile
Growth
Share
Near-Term Path Model
BENEFIT: +
+
Roadway
Speed –
DEMAND:
VMT
Growth
Share
Other factors affecting development: What
other factors influence development
patterns? Access alone is not sufficient
to trigger development. Other key
public facilities like sewer and water
may need to be available to the study
area at a reasonable cost. If they are,
improvements in access are more likely
to support land use change.
Other market factors: Where has growth
been going? How does this trend
correspond with current plans and
zoning? Are access, travel time or
other factors limiting conditions on
development in the study area?
SUPPLY:
Lane Mile
Growth
Share
+
+
Cervero’s Longer-Term Path Model
–
Longer-Term Path Model
BENEFIT:
Roadway
Speed
+
DEVELOPMENT
ACTIVITY:
Building Growth
Share
+
–
+
+
DEMAND:
VMT
Growth
Share
Near term
Longer term
source: Robert Cervero
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