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OCR for page 96
Directions for Coordinated Improvement
of Travel Surveys and Models
Eric Petersen, RAND Europe
Peter Vovsha, PB Consult, Parsons Brinckerhoff Inc.
A
number of recent studies have pointed out the gap deficiencies of such models was the matrix structure of
between academic interest in activity-based models the trip distribution and modal-split submodels that
and the relative scarcity of activity-based models severely limited the model segmentation and the number
implemented for regional and statewide planning agencies. of explanatory variables that could be used. The surveys
The issues that hinder the adoption of activity-based mod- were actually much richer than the models, and it was
els range from the difficulty in obtaining both resources to not clear why travel surveys should be made even more
reestimate existing models and staff to run more compli- complicated (and more expensive to collect). Shifting to
cated models to theoretical concerns over the variability the microsimulation modeling paradigm has lifted this
involved in microsimulation. This paper focuses on the data technical limitation from model segmentation, allowing
requirements to support the estimation of an activity-based for richer, more-complex models, and, in turn, fueling
model and will present the minimum requirements and the the desire for better data.
desirable features to be included in future household sur- There are several directions in which travel demand
veys. The underlying message of this paper should reassure models and corresponding surveys can be significantly
planning directors that the basic surveys required to build improved:
an activity-based modeling application are similar to those
required to update and revalidate a conventional model, 1. Widening the range of explanatory variables used
although certain extensions are desirable. A focus on more in models and collected in surveys,
limited improvements to conventional surveys does not rep- 2. Improving the understanding and modeling of
resent a digression from a move toward activity-based causal linkages across various dimensions of travel
models but rather offers a useful intermediate stop on the behavior, and
way and takes practical advantage of what can be already 3. Adding attitudinal and SP extensions to conven-
done today or in near future. For modelers wishing to tional revealed-preference (RP) surveys.
explore the cutting edge of activity-based modeling, the
paper also examines two promising areas of research: atti- Each of these points is described below in detail.
tudinal and stated-preference (SP) extensions to conven- These three directions are not independent and actually
tional surveys. The paper concludes with a survey of are closely intertwined. Furthermore, model improve-
existing household surveys from large metropolitan regions ment can proceed in incremental steps rather than
in North America and Europe and examines their suitabil- requiring dramatic improvements in all three areas
ity for supporting activity-based models. simultaneously. In a resource-constrained environment,
For a long time, the structure of travel surveys was the most practical approach may be to conduct a survey
limited by the considerations of supporting the develop- for a convention model, but the authors strongly recom-
ment of conventional four-step models. One of the major mend that the standard surveys be enhanced with some
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