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4 I N N O VAT I O N S I N T R AV E L D E M A N D M O D E L I N G , V O L U M E 1
aggregate analysis has been resolved, with general agree- expect from the modeling community. I would like you
ment on the use of disaggregate analysis. Advances in dis- to write down four items to remember: (a) what you do
crete choice modeling include the use of multinomial and is very important; (b) things are changing very rapidly;
nested logit models, generalized extreme value models, (c) things are changing faster than our ability to respond;
and mixed logit models. These models better represent and (d) under certain circumstances, we need to change
complex choices and substitutions among those choices. the foundation of the way we do our jobs.
Addressing computation-related issues has been Figure 4 highlights the role of MPOs in the trans-
helped by the development of enhanced algorithms for portation decision-making process. I think Keith Lawton
many aspects of transportation analysis. The adoption and others in the Portland area deserve a great deal of
of microsimulation in travel prediction and in transport credit and thanks for the work they have done on testing
systems operations has also been a major improvement. activity-based models and other applications. I think all
Enhanced data collection and processing has enhanced MPOs have an obligation to the modeling community--
analysis techniques for control purposes. not just as users of models, but also as developers and
There have been significant advancements in land use testers of models.
modeling. We have also seen improvements in our abil- MPOs receive guidance from the U.S. Department of
ity to represent spatial detail and realistic land market Transportation, citizens, local jurisdictions, and policy
representation. There has been increased application of makers. Many MPOs are involved in sharing experiences
geographic information systems (GIS) in transport sys- with different models and applications. Within Texas,
tem components, trans-shipment terminals, and land use we have partnerships to help integrate models across the
components. state. I think MPOs should be more involved in collabo-
Dynamic assignment is one of the most central issues rative research and we should be encouraging more part-
related to transportation service representation. How- nerships with the private sector and with universities. We
ever, to be effective, such analysis must be informed by a all have an obligation to increase communication, and
good time-of-day representation of demand. Other issues by increasing communication we can help advance the
include spatial detail, consistency across levels of detail, state of the practice, the state of the art, and the decision-
refinement of travel supply functions, and enhanced making process.
operational control. Models are not an end to themselves. Travel models
Despite the tremendous progress that has been made, are a tool to help in the decision-making process. I think
we continue to need an increased understanding of behav- we are on the verge of a new foundation in travel mod-
ioral responses. Both modelers and policy makers need to els. Too often in the past, the information system and the
understand why we sometimes get unintended conse- model system have been the same. We often have a prob-
quences from decisions that seem wise based on travel lem with the public and policy makers confusing the
forecasts. We also need a better ability to focus on small steps in the transportation planning process and the steps
areas or population groups, as well as the ability to rep- in the modeling process.
resent more complex behaviors in models. As we learn Figure 5 illustrates the role that travel models play in
more about what we know and what we do not know, the implementation process. I think there has to be a
the limitations of existing models become more obvious. broader information system that creates a foundation
Other issues that need to be addressed include for the whole transportation planning process. Travel
improved presentation of all the aspects of transportation models then become part of this broader foundation.
and activity-based analysis, including supply, demand, Travel models, land use models, goods movement mod-
and land use. One of the core issues is the need for better els, and inputoutput models are all needed.
communication between modelers and decision makers. As Frank Koppelman noted, I think one shortcoming
Modelers need a fuller understanding of policy issues and is that we do not spend enough time interpreting the
to improve the presentation of modeled impacts to policy model results. The goal of travel models is not to forecast
makers. Modelers and decision makers also need to the exact number of vehicles that will use a collector
expand the range of decision options to be examined. street in 2010. The goal is to interpret what that number
means.
One important issue is the different scales for fore-
STATE AND LOCAL AGENCY PERSPECTIVES ON casting tools and the need for consistency. We need a
POLICY ISSUES: ONE SIZE DOES NOT FIT ALL strong national transportation system that includes
national transportation data sets. The national data need
Michael Morris to be integrated into statewide data sets. Within Texas,
new intercity corridors, called the Trans-Texas Corri-
This is a very critical conference at a very critical time. dors, are being developed. Tools are needed to assess
My remarks focus on what state and local officials travel in these corridors that are consistent with those
