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M O V I N G I N N O VAT I V E M O D E L S I N T O P R A C T I C E 11
age. Activity-based models allow for a richer household DEVELOPING DETAILED PROJECTIONS OF
composition and market segmentation. IMPACTS OF SPATIAL SEPARATION, MITIGATION,
Static equilibrium assignments are important. After SUPPLY AND DEMAND, INFRASTRUCTURE, AND
level of service E is reached, volume demand functions STRATEGIES IN A VOLATILE ECONOMIC, SOCIAL,
are questionable. This issue affects mode choice, air qual-
AND PHYSICAL ENVIRONMENT
ity analysis, activity location choice, and time-of-day
choice. Volume-to-capacity ratios do not necessarily pin-
point problems in a way that can be prioritized. The lack Edward Granzow
of vehicle dynamics, such as acceleration and stopping,
makes analysis of air quality issues a problem. My comments focus on software systems and their appli-
The general assumption of a static land use compo- cation in travel modeling. As we consider travel demand
nent negates the effect of infrastructure investments on models, it is important to focus on the uses of these mod-
housing and job location. It does not consider the effects els. This approach helps us to better understand what the
of not building sufficient transportation infrastructure various models can and cannot do, where we stand in terms
on land use. Static land use assumptions can either of current and expected innovative practice, and challenges
underestimate or overestimate needs. we still face. My comments focus on both operational and
I would like to offer a few suggestions on the direction theoretical aspects of travel modeling. Any approach we
in which modeling should be moving. First, we need to take will have potential costs and benefits in terms of the
move toward the use of tour-based or better activity-based operational environment and in terms of the theory.
models. Second, we need to continue to develop large- It is important to remember that we are moving from
scale microsimulation or large-scale dynamic traffic a modeling environment that is fairly flexible and easy to
assignment (DTA) models. Third, there is a need to deploy use, and that has benefits to MPOs in solving real-world
integrated land use models for major planning exercises. problems, into an environment where there is a lot more
There are some limitations with the current tour- fidelity. There are a number of items that are important
based models. The model structure is typically similar to to consider in moving toward more widespread applica-
the trip-based model structure, which begins with activ- tion of advanced models.
ity location and mode. It is possible to improve on the The innovations in travel models that we are dis-
trip-based approach, however, because the activity pat- cussing are phenomenal, but more work is still needed
tern is known at mode choice. With network microsim- before we will see widespread application. It is impor-
ulation, it becomes evident that location choice for tant to remember that advanced travel demand models
transit users and walk trips might be fundamentally dif- are not a magic solution.
ferent than for automobile trips. There is still uncertainty related to the future demands
There is a lot of activity focused on current microsim- that we may face as modelers and I do not think that we
ulation and DTA limitations. TRANSIMS provides an have a coherent strategy for addressing these demands.
approach to addressing many concerns, including the We need a broader perspective as we examine the future
need for more scale and more granularity. of travel demand modeling. The title of my presentation,
There are limitations with currently available land use Developing Detailed Projections of Impacts of Spatial
models. Some of these limitations focus on competing Separation, Mitigation, Supply and Demand, Infrastruc-
technologies and tools that add complexity, as well as ture, and Strategies in a Volatile, Economic, Social, and
additional staff and financial resource needs. Land use Physical Environment, highlights some of these points.
modeling should be attempted, however, even if it is only The first few words are the key part of the title. Most
a simple approach. A simple technique can begin the of the words after that are modifiers. As modelers, we
institutionalization of using land use models with techni- are being asked to provide more information about the
cal staff and policy makers. future. We are being asked to deal with a larger number
We need to continue to focus on bridging the gap of varied assumptions as model inputs. I use the concept
between the use of trip-based models and the use of more of "feasible regions" to potentially identify an area of a
advanced tour-based models. Tour-based models are in graph that represents the possible outcome of a situation
practice in a few places, but additional implementation is given a number of model runs. Models are more com-
needed. There are still some improvement needs with plex today. This complexity may limit the viability of
tour-based models, but they produce better results than models to conduct "what if" analyses. Also, the cause
trip-based models. Minor improvements from common and effect and impact chains become less clear. Model
postprocessing are not enough with assignment. There is complexity can obscure practical applications.
a need to explore other available methods. We have The three words--spatial, separation, and mitigation--
much to learn from the experiences with the use of dif- relate to the way in which telecommunications is interact-
ferent models in different areas. ing with transportation. Telecommunications is changing
