| The
Authority's Travel Demand Models |
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| Both
the Measure C Growth Management Program
and the State congestion management
legislation require the Authority
to develop and maintain travel demand
models. These models use information
on current and future population and
employment, expected roadways and
transit systems, and observed travel
behavior. From these inputs, the models
forecast traffic on the regional transportation
system. The first models were developed
in the early 90s, one for each of
the four sub-areas of Contra Costa.
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| The
travel demand models are useful in
several ways. Local jurisdictions
use them to analyze the effects of
new developments and changes in their
general plans. The Authority and other
agencies use them to analyze the effects
on new transportation improvements.
And the Authority uses the Central/CMP
model to analyze the effects of its
plans and programs, including the
Countywide Comprehensive Transportation
Plan and the Congestion Management
Program. |
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Park
& Ride Patch for the CCTA Countywide
Model
Recently an error was observed in
the Park & Ride algorithm for
the CCTA Countywide Model. In some
cases, the model may double count
trip assignments destined for Park
& Ride facilities. A technical
bulletin and the corresponding files
(compressed) to correct the problem
are listed below:
Technical
bulletin
CCTA_PnRfix.zip
Whether
the error exists in your model version
or not, this patch may be safely
implemented.
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| The
Decennial Model Update |
| A
considerable amount has changed since
the Authority began preparing its
first models. Computing power has
increased at an exponential rate,
and we have seen significant improvements
in modeling software and closely related
tools of the trade, such as Geographic
Information Systems (GIS). To take
advantage of these improvements and
to reflect the substantial changes
in the population, jobs and transportation
networks since the early 1990s, the
Authority undertook a decennial update
of its model. This effort began with
data collection in 1999, and was completed
when the new countywide model became
operational in 2003. |
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| The
updated model significantly restructures
the Authority’s modeling approach.
The update combined the four detailed
subarea models into a single fine-grained
countywide model. This updated model
contains approximately 1,700 zones
in Contra Costa and the Tri-Valley,
and it retains the 1,099 zone-structure
of MTC’s model for the remainder of
the Bay Area, resulting in a model
with approximately 2,700 zones in
total. The decennial update also involved
software conversion from the previous
EMME/2 platform to the GIS-based TransCAD®
system. |
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Model
Documentation
A
compendium of the modeling documentation
is available and downloadable from
the Growth
Management publications page
in the Technical Documents section.
The modeling documentation includes
a user's guide, the land use data
dictionary and the highway link
data dictionary.
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Special
Generator Patch for the CCTA Countywide
Model
Recently it was
observed that the 4 digit TCID tag
was not updating correctly.
As a result, the TAZ correspondence
table may include an incorrect TCID. A
technical bulletin and the corresponding
files to correct the problem are
listed below:
Technical
bulletin
SP
Gen List
SP
Gen List 25
SP
Gen List 30
Whether the
error exists in your model version
or not, this patch may be safely
implemented.
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| Seeing
the Model on the Web |
| The
volume plots from the current model
may be viewed by clicking on the link
below:
Click
on the below links to access November
2006 model output plots for the
number of lanes in the network and
the traffic volumes for various
time periods
A separate
Modeling Web Site has also been
established for use by qualified
model users who have familiarity
with the TransCAD software and who
are involved in reviewing draft
model input assumptions used to
update the model outputs. Visitors
to the modeling web site can view
the various components of the model,
including the traffic analysis zones,
the transportation network, and
much of the detailed input and output
information used in the model. This
information includes the household
and employment information for each
TAZ, and the lane, speed, type and
other data associated with the different
parts of the network. Furthermore,
aerial photographs of the modeling
study area (Contra Costa only) are
displayed on this modeling website,
which requires a user name and password
to access.
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| The
Land Use Information System |
| The
Authority also maintains the information
necessary to run these models. The
land use, demographic and economic
information is contained in the Land
Use Information System (LUIS). |
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| The
Comprehensive Transportation Project
List |
| To support
the modeling tools, as well as various
planning and programming efforts,
the Authority maintains a database
of current and proposed transportation
projects, the Comprehensive Transportation
Project List. We ask local agencies
to provide us with information on
important local projects so that we
this important database up-to-date. |
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