Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 42
42
CHAPTER 8
Case Studies
The model components, class of models, data, and other Objective and Purpose of the Model
statewide freight forecasting issues discussed elsewhere in this
What need will the forecasting model address? How will
Toolkit are not theoretical exercises. They are issues that trans-
the model be used?
portation planners have confronted and will continue to con-
front. So that users of the Toolkit may have the benefit of the
experiences of other planners and may see actual applications General Approach
of the techniques, 10 case studies have been prepared. Two case
studies have been chosen for each of the model classes defined Model class
in the Toolkit. The cases studies draw widely from the various Choose from one of the following:
model components, and represent a variety of data source
applications. To the extent possible, the results of the coeffi- · Flow Factoring;
cients, parameters, equations, validation, and other aspects of · O-D Factoring;
the case studies have been presented so that users of this Toolkit · Truck Model;
can compare their results with the results obtained by others. · Four-Step Commodity Model; and
The case studies have been presented using a common · Economic Activity Model.
template, presented in Section 8.1. This template not only
permits easy comparisons between case studies, but also
serves as a useful organizing principle for anyone undertak- Modes
ing a statewide freight forecasting project. Answering the
What freight modes will the model address?
questions in the template helps freight forecasters better un-
derstand the specific issues they must face and the choices
they can make given the available techniques. Markets
This Toolkit is intended to present useful information on
a variety of techniques in an accessible format. No single What is the nature of the market that the freight forecast-
approach can be considered the correct one, nor does the use ing model must cover (geographic, industries, etc.)?
of one approach preclude the possibility of using another in
the future. By answering the questions in the template, users Framework
should be able to develop an approach that best addresses
their specific needs. Will the freight model work within a larger process of
preparing transportation forecasts for nonfreight demand,
such as passenger travel? If it will be part of a larger process,
8.1 Development of a Forecasting how will the freight model be included?
Model Template
Background
Flow Units
Context
What flow units will the model be expected to report (an-
What is the nature of freight movement in the area for nual tons, daily trucks, daily trucks by truck type, etc.)? Will
which the forecast model will be developed? the flow units differ for the individual modal networks?
OCR for page 43
43
Data example, from annual to daily flows)? How will these conver-
sion factors be obtained? If the conversion factors will be de-
Forecasting Data veloped specially for this model, what data source will be used
BASE AND FORECAST YEAR SOCIOECONOMIC DATA to develop these conversion factors?
What base year data is available to support the model?
What geographic units are available? What is the industrial Validation Data
breakdown? Is forecast data available, and if so what level of Which of the model components will be validated using
geographic and industrial detail is available? Is the forecast data obtained independently of the model development?
data developed by a land use/economic model? Is such a What is the source of this data? How will it be used?
model to be integrated with the freight transportation model?
Model Development
EXTERNAL MARKETS
Software
What data is available for the geographic area outside of
the state or primary study area? Is base data available on the What software programs will be used in the development
amount of freight that travels to and from these external mar- of this model? What software programs will be used in the
kets and the state or other primary study area? Is base data operation of this model?
available on the amount of freight that travels between these
external markets passing though the state or other primary
Commodity Groups/Truck Types
study area? What level of geographic and industrial detail is
available? Is forecast data available, and if so at what level of Will the freight flow units of the model be distinguished by
industrial detail? purpose? For commodity models, what commodity groups
will be separately included? Are these aggregations of existing
Modal Networks commodity classification schemes? For truck models, what
truck types will be separately included?
FREIGHT MODAL NETWORKS
Are existing travel demand model networks for any of the Trip Generation
freight modes to be included in the model? Does sufficient
data exist to develop any missing modal networks? Are modal Will a trip generation component be included? If so, how
networks that cover any external zones to be included in the will the trip generation rates be developed? For production?
model? For attraction?
INTERMODAL TERMINAL DATA Trip Distribution
Is data available on intermodal terminals where freight Will a trip distribution component be included? If so, will
changes modes (ports, airports, and rail terminals, for exam- a gravity model or some other model form be used? How
ple) that might be included in the model as special genera- will the model parameters and equations be developed?
tors? Does this data include information on the location and
capacity of the terminals? Does this data include demand/ Commodity Trip Table
usage data for the terminals?
If neither a trip generation model nor a trip distribution
model will be included, will an existing origin-destination
Model Development Data
table of freight flows be obtained for inclusion in the model?
Will model coefficients and parameters be developed How will this table be updated for forecasts?
specifically for this model? If so, what data will be used to
develop these parameters and coefficients? Mode Split
Will a mode split model be included in the model? Will
Conversion Data
this component primarily rely on existing mode splits? If so,
Will the model need to convert flows from one unit to where will those existing mode splits be obtained? Will the
another (for example, from tons to vehicles)? Will the model existing mode splits be modified qualitatively based on
need to convert flows from one time unit to another (for expert opinion? Will the existing mode splits be modified
