Why Dynamic Traffic Assignment?
FROM A TRANSPORTATION PLANNING PERSPECTIVE
Travel forecasting models are used in transportation planning to evaluate the impact of future
changes in demographics, land use, or transportation facilities on the performance of a region’s
transportation system. Traveler behavior is introduced into these forecasting models through
sequences of modeling steps. The traditional four-step process, for example, results in travel
choices made by groups of homogeneous travelers in aggregate trip-based models. More
advanced activity-based processes seek to represent travel choices made by individual travelers.
Cost and time of travel are key components of all travel models throughout the entire
sequence of model steps. For example, a household’s choice of the number of personal vehicles
to own is often forecast subject to aggregate measures of the accessibility of the household. The
less accessible a household is, the more likely it is to own automobiles. An accessibility
measure is then some representation of the travel time and cost from the residence to work places
or shopping places. Likewise, time and cost are clearly significant factors in other choices made,
including residential, workplace, and discretionary activity locations, as well as factors in
deciding which transportation services to use and which routes to follow when engaging in
travel.
From a travel forecasting perspective, the time and cost of travel are critical factors.
Those measures are also critical in quantifying impacts on a regional scale for the purpose of
informing policy decisions. Travel time and cost measures determined using static network
analysis (assignment) procedures use variables of interest that are time-invariant. It has become
increasingly evident that these procedures are inadequate as explanations of influences on travel
choices and as measures used to evaluate impacts when deciding how to develop policies for
managing transportation systems, how to fund transportation system improvements, and how to
measure environmental impacts related to systemwide travel.
Dynamic network analysis models seek to provide another, more detailed means to
represent the interaction between travel choices, traffic flows, and time and cost measures in a
temporally coherent manner (e.g., further improve upon the existing time-of-day static
assignment approach). More specifically, dynamic traffic assignment (DTA) models aim to
describe such time-varying network and demand interaction using a behaviorally sound
approach. The DTA model analysis results can be used to evaluate many meaningful measures
related to individual travel time and cost, as well as systemwide network measures for regional
planning purposes.
Why Dynamic Traffic Assignment?
FROM A TRANSPORTATION PLANNING PERSPECTIVE
Travel forecasting models are used in transportation planning to evaluate the impact of future
changes in demographics, land use, or transportation facilities on the performance of a region’s
transportation system. Traveler behavior is introduced into these forecasting models through
sequences of modeling steps. The traditional four-step process, for example, results in travel
choices made by groups of homogeneous travelers in aggregate trip-based models. More
advanced activity-based processes seek to represent travel choices made by individual travelers.
Cost and time of travel are key components of all travel models throughout the entire
sequence of model steps. For example, a household’s choice of the number of personal vehicles
to own is often forecast subject to aggregate measures of the accessibility of the household. The
less accessible a household is, the more likely it is to own automobiles. An accessibility
measure is then some representation of the travel time and cost from the residence to work places
or shopping places. Likewise, time and cost are clearly significant factors in other choices made,
including residential, workplace, and discretionary activity locations, as well as factors in
deciding which transportation services to use and which routes to follow when engaging in
travel.
From a travel forecasting perspective, the time and cost of travel are critical factors.
Those measures are also critical in quantifying impacts on a regional scale for the purpose of
informing policy decisions. Travel time and cost measures determined using static network
analysis (assignment) procedures use variables of interest that are time-invariant. It has become
increasingly evident that these procedures are inadequate as explanations of influences on travel
choices and as measures used to evaluate impacts when deciding how to develop policies for
managing transportation systems, how to fund transportation system improvements, and how to
measure environmental impacts related to systemwide travel.
Dynamic network analysis models seek to provide another, more detailed means to
represent the interaction between travel choices, traffic flows, and time and cost measures in a
temporally coherent manner (e.g., further improve upon the existing time-of-day static
assignment approach). More specifically, dynamic traffic assignment (DTA) models aim to
describe such time-varying network and demand interaction using a behaviorally sound
approach. The DTA model analysis results can be used to evaluate many meaningful measures
related to individual travel time and cost, as well as systemwide network measures for regional
planning purposes.
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