TransCAD is the most comprehensive, flexible, and capable travel demand
modeling software ever created. TransCAD supports many styles of travel
demand modeling including sketch planning methods, UTPS-style four-step
demand models, advanced disaggregate modeling techniques, simultaneous
models for multiple choices, and the most extensive set of traffic
assignment models ever assembled for use by planners and traffic
engineers.
TransCAD breaks new ground as a tool for transportation planners by streamlining and improving the demand modeling process. TransCAD is the only package designed to facilitate the implementation of best practices for travel forecasting and to provide a mechanism for advancing the state of the art in transportation modeling. Modeling with TransCAD is not limited to urban or regional demand forecasting, but is directly applicable for modeling passenger and freight flows at the state, national, and international level.
Travel forecasting models are used to predict changes in travel
patterns and the utilization of the transportation system in response to
changes in regional development, demographics, and transportation
supply. Modeling travel demand is a challenging task, but one that is
required for rational planning and evaluation of transportation systems.
TransCAD is the only planning package that is GIS-based and fully
integrates geographic information system (GIS) and demand modeling
capabilities. TransCAD is an extremely capable and robust GIS that
includes many advanced features for transportation that are not
available in other products.
There are many reasons why it is valuable to have a GIS as part of a
travel demand forecasting package. First, GIS makes it possible for
planning models to be much more accurate. For example, network distances
are based on the actual shape of the road network and a correct
representation of highway interchanges.
Second, the whole modeling process is more efficient. Data preparation
is greatly facilitated and the database and visualization capabilities
catch errors before they cause modeling problems. With TransCAD, you and
others will have an easier time understanding how the model components
behave. For all of these reasons, less staff time is needed to implement
and maintain travel models.
A third important advantage of a GIS-based modeling system is the use of
the GIS itself and GIS-derived measurements directly in the modeling
process. In TransCAD, different modeling equations can easily be derived
and applied for different geographic subareas. Similarly, TransCAD
brings new and much-needed capabilities for measuring geographic
accessibility.
Because they have similar architectures, TransCAD is the planning
package that integrates best with other institutional GIS systems.
TransCAD can import data from virtually all major GIS, CAD, and planning
software packages. TransCAD is an open system and can export data in
ASCII, shape files, dxf, and dbf formats. TransCAD also links easily to
ArcView, ArcInfo, MapInfo, GIS+, and Maptitude.
Standard TransCAD includes comprehensive tools for trip generation, trip distribution, mode split modeling, and traffic assignment. TransCAD includes all of the traditional UTPS models, quick response models with reduced data requirements, and advanced disaggregate demand models. Caliper continually enhances TransCAD to incorporate the most up-to-date methods for demand forecasting.
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The goal of trip production is to estimate the number of trips, by
purpose, that are produced or originate in each zone of a study area.
Trip generation is performed by relating frequency of trips to the
characteristics of the individuals, of the zone, and of the
transportation network.
There are three primary tools that are used in modeling trip production, all of which are provided in TransCAD:
Cross-Classification: Cross-classification methods separate the population in an urban area into relatively homogenous groups based on certain socioeconomic characteristics. Then, average trip production rates per household or individual are empirically estimated for each classification. This creates a lookup table that may be used to forecast trip productions. In TransCAD, you can use your existing look-up tables, create new ones from survey data, and edit any of the values. TransCAD provides several default cross-classification tables including those for quick response methods.
Regression Models: TransCAD supports estimation and application of multivariable aggregate zonal models and disaggregate models at the household or individual level. The first method uses data aggregated at the zonal level, with the average number of trips per household in the zone as the dependent variable and average zonal characteristics as the explanatory variables. The second method uses disaggregate data at the household or individual level, with the number of trips made by a household or individual as the dependent variable and the household and personal characteristics as the explanatory variables.
Discrete Choice Models: Discrete choice models use disaggregate household or individual level data to estimate the probability with which any household or individual will make trips. The outcome can then be aggregated to predict the number of trips produced.
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Trip AttractionThe goal of Trip Attraction is to predict the number of trips attracted to each zone or to a particular land use. In many ways, estimating attractions is similar to estimating trip productions. Thus, cross-classification, regression, and discrete choice methods can be used to estimate the number of trips attracted to a zone. TransCAD also includes Institute of Transportation Engineers (ITE) trip rate data for calculating trip attraction values for a single land use or mixed land uses.
In trip generation, separate models are used to predict productions and attractions. This invariably leads to a discrepancy between the number of intraregional trips produced in an area and the number of trips attracted to an area. To conserve trips, balancing methods are provided so that the number of attractions equals the number of productions. Trip generation and attraction can be balanced flexibly to productions or attractions or a linear combination thereof.
Trip distribution models are used to predict the spatial pattern of trips or other flows between origins and destinations. Models similar to those applied for trip distribution are often used to model commodity flows, retail trade, and store patronage.
TransCAD provides numerous tools with which to perform trip distribution, including procedures to implement growth factor methods, apply previously-calibrated gravity models, generate friction factors, and calibrate new model parameters.
In addition to doubly constrained trip distribution models that ensure that the output flow matrix from trip distribution matches the input productions and attractions, TransCAD includes tri-proportional models which allow for another dimension of constraints. In tri-proportional models, groups of cells in the P-A flow matrix are required to sum to specified values. TransCAD allows the additional dimension to be applied for both growth factor and gravity models.
Mode choice models are used to analyze and predict the choices that individuals or groups of individuals make in selecting the transportation modes that are used for particular types of trips. Typically, the goal is to predict the share or absolute number of trips made by mode.
An important objective in mode choice modeling is to predict the share of trips attracted to public transportation. TransCAD provides procedures for calibrating and forecasting mode choice models based on logit, regression, and cross-classification, and may be pursued at either a disaggregate or aggregate zonal level.
Estimation of the parameters in the multinomial logit model is performed in TransCAD by the method of maximum likelihood, which calculates the set of parameters that are “most likely” to have resulted in the choices observed in the data.
TransCAD supports choice set variation in both estimation and model application which is important for accurate model specification. TransCAD also provides support for nested logit models and for coding user-defined mode choice procedures in FORTRAN and C.
TransCAD includes comprehensive tools that enable you to:
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Traffic assignment models are used to estimate the flow of traffic on
a network and allow you to establish the traffic flow patterns and
analyze congestion points. TransCAD provides a full complement of
traffic assignment procedures that are used for modeling urban traffic.
These procedures include numerous variants that are tailored for
modeling transit, as well as intercity passenger and freight traffic.
These models take as input a matrix of flows that indicate the volume of traffic between origin and destination pairs. The flows for each O-D pair are loaded on the network based upon the travel time or impedance of the alternative paths that could carry this traffic.
Basic Traffic Assignment Methods available in TransCAD include:
TransCAD also provides a wide variety of options available for the traffic assignment procedures. There is user control over link performance functions and parameters, treatment of transfer and turning penalties, pre-loading of network links, and calculation of additional output measures. These user controls are very conveniently set with system defaults and the ability to code exceptions for specific links and intersections. Critical link analysis is another traffic assignment option.
TransCAD produces individual and cumulative frequencies of different link volume ranges in both absolute and percentage terms, and the same information for volume-to-capacity ratios.
One output option is to generate data on cold start traffic. When this option is selected, TransCAD keeps track of the location and volume of traffic that is in the cold start mode. This quantity is required for air quality impact estimation.
TransCAD also provides many advanced traffic assignment procedures. These include procedures for:
Public transit is a speciality of TransCAD, with capabilities that greatly exceed those of other planning packages. TransCAD has special data structures for handling transit routes in all their natural complexity. Routes may be stored, displayed, edited, and analyzed. An important feature is that transit routes can be directly placed on the streets so that interactions between autos and transit can be treated explicitly.
Special visualization capabilities for transit make it easy to display and label overlapping routes. There is an effective interactive route editor that makes it straightforward to enter new routes and modify existing ones.
TransCAD has the broadest set of transit pathfinding routines of any package and includes the methods found in other packages. The latest version has a new, generalized pathfinder that computes composite characteristics for overlapping transit routes. This pathfinder improves upon the UTPS, MINUTP, and EMME/2 methods and gives a good estimate of the waiting time that travelers would experience prior to boarding a transit route.
There are also the broadest set of transit assignment methods including some innovative methods not found in other packages. These include a stochastic user equilibrium method that deals with multiple service alternatives, vehicle capacity, and optionally with dwell time and user’s value of time. In New York City, the transit agencies have been using TransCAD for nearly a decade now because of these advanced capabilities.
TransCAD has special tools and procedures for creating and working with transit networks. Transit fares can be specified as either flat or zonal. Using transit networks and fare structures, you can solve shortest path problems and calculate transit path attributes (i.e. skims).
Transit networks are used for the following:
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Transit assignment models are used to estimate the number of passengers
that utilize links in a transit network as a function of transit level
of service. These models take as input a matrix of passenger flows
between origins and destinations and a transit network, and produce link
level and aggregate ridership statistics. TransCAD includes an array of
sophisticated transit network assignment procedures.
The transit assignment procedure lets you choose from six different assignment methods:
The first four are non-equilibrium methods. The last two models are equilibrium assignments, which take account of the capacity of transit service and the effect of ridership on crowding comfort and, optionally through dwell time effects, and travel time on the route. These methods distribute the flow between a particular origin and destination to multiple paths, based on their relative attractiveness.
The transit assignment procedure produces a table of ridership at every stop along each route in the transit network. Optional outputs include critical link analysis, boarding and alighting counts, and aggregate ridership counts.
With TransCAD you can have separate and fully integrated networks for bicycles and pedestrians. Pedestrian links can be full street networks. Walk links can be included in transit networks.
Accurate and up-to-date trip tables are critical inputs for transportation planning models. Traditionally, the principal method of collecting information on the spatial pattern of trips within urban areas has been the large scale home interview survey. Unfortunately, home interview surveys of the necessary sample size are prohibitively expensive and difficult to implement, and are therefore rarely done. In contrast, traffic counts on highway links are inexpensive to perform and are routinely collected in many areas. It is thus extremely attractive to have a method to create or update trip tables based upon traffic counts.
TransCAD provides a very flexible and effective procedure for estimating and/or updating an origin-destination matrix based upon a sample of network link traffic counts and an optional, initial or base trip table.
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Standard TransCAD has been designed to facilitate freight demand
modeling as well as passenger models. An innovative Freight Dashboard™
provides an efficient interface for retrieving freight flow data by
origin, destination, mode, and commodity. TransCAD offers a complete
solution for modeling commodity flows and truck movements. Freight
traffic can be easily assigned to the transportation network and there
are also specialized assignment procedures available for rail waybill
assignment.
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New editing tools provide an effective means of improving the geography
and topology of planning networks that may have only simple,
straight-line representations.
Specifically, Standard TransCAD includes tools for:
Consequently, planning networks can now be fully realized as GIS entities and visualized directly with appropriate accuracy, shape, geometry, and directionality. Many users will find these tools indispensable for transforming TIGER/Line layers into a suitable basis for planning and traffic applications as well as for improving the line layers that are used for other types of transportation, including rail, transit, and air networks.
TransCAD includes utilities that model builders will find indispensable for data preparation.
