Planning and Travel Demand Modeling with TransCAD

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.

Demand Forecasting in a GIS Context

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.

SATURN Support

Standard TransCAD for Great Britain works in conjunction with SATURN (Simulation and Assignment of Traffic to Urban Road Networks). Any user with a valid license of SATURN can maintain databases and set up runs from within TransCAD. TransCAD will also post process SATURN outputs and present them as tables and map displays.

SATURN is widely used in Great Britain as a combined simulation and assignment model for the analysis of traffic management schemes. If you are a SATURN user, the SATURN traffic assignment interface in TransCAD for Great Britain enables you to run SATURN simulation/assignment programs, with data preparation and results displayed in the powerful TransCAD for Great Britain GIS-based platform. The interface reads the required and optional data prepared into TransCAD for Great Britain and converts them to SATURN input files, then calls the appropriate SATURN programs. If SATURN runs successfully, the interface reads selected SATURN output results back into TransCAD for Great Britain.
 
Data preparation in TransCAD for Great Britain is straightforward; for example, there is no need to enter link and turn data in a given order. In fact, all the node, link and turn data can be entered in an arbitrary order. The interface will take care of sorting them as required by SATURN. The display and analysis of assignment results are conveniently integrated with the GIS capability of TransCAD for Great Britain. All SATURN input and output files generated during the process are stored in your preferred folder, so that you can retrieve them if needed.

Modeling Capabilities

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.

The Standard Version of TransCAD includes procedures for:

• Trip Generation/Production
• Trip Attraction
• Trip Balancing
• Trip Distribution
• Mode Split and Choice Analysis
• P-A to O-D and Time of Day Transformations
• Traffic Assignment
• Advanced Highway Assignment
• Public Transit
• O-D Matrix Estimation

Freight Applications

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.

Programming TransCAD

TransCAD comes with its own application environment and scripting language called GISDK(TM). GISDK lets you create add-in applications, transportation data and visualization servers, and web applications.

Innovative Batch Processing
There is an innovative batch processing system that is built in to TransCAD. In addition to creating scripts the old fashioned way by writing them from scratch, TransCAD lets you create scripts interactively by clicking menu items, choosing parameters in dialog boxes, and saving the corresponding script. This can then be edited further in the conventional manner.
Caliper also provides templates for common modeling streams including feedback so that you can adapt the templates for your own purposes. The GISDK and the batch facility let you create beautiful Windows user interfaces for your models.

Linking to other Models
Add-ins can be easily created for TransCAD to customize its use and to link in other models for post-processing of many types. Caliper provides links to some important planning applications such as air quality models.

Creating Other Types of TransCAD Applications
TransCAD is an OLE automation server. This means that TransCAD macro functions can be called from Visual Basic, Visual C++, and other programs. This facilitates the creation of custom add-ins and stand-alone applications. It also makes it easy to create web applications.

Advanced Geographic Editing Tools

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:

• Dualizing, merging, and setting directionality of segments
•  Improving the geographical accuracy of line segments through conflation
•  Copying and pasting line segments from one layer to another
•  Creating highway interchanges with a minimum of effort.

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.

Data Access and Planning Utilities

TransCAD includes utilities that model builders will find indispensable for data preparation.

Geocoding: Virtually all forms of survey data can be analyzed in TransCAD. For most modeling purposes, each survey will be geocoded to the respondent’s primary location. For traveler surveys, each survey will most commonly be geocoded to their residence.

Import Networks and Trip Tables: TransCAD provides tools for importing networks and network data from a variety of stand-alone transportation planning packages. These networks are converted into GIS databases that can be used for all types of planning, modeling, and mapping applications. TransCAD provides a seamless import capability for transportation planning network files in MINUTP, EMME/2, TRIPS, QRSII, and TRANPLAN ASCII format. Usually preprocessing of the original files is not required.

Screenline Analysis: Screenline analysis compares the results of trip assignment with the traffic counts on roads. More precisely, it is a process of comparing the directional sum of ground count traffic volumes across a screenline or a cordon line with the directional sum of the assigned traffic volumes across the same screenline or cordon line. Screenline analysis is a useful tool for the calibration of trip assignment models, and it can also be used for more general purposes of calculating flows that cross a screenline.

Subarea Focusing: While forecasting transportation demand for a region, you may be interested in performing a more detailed investigation of traffic patterns within a subarea, such as the downtown area. To facilitate subarea analysis, TransCAD provides a procedure that lets you create an O-D trip table for that subarea. The reduced O-D table may be used for performing a traffic assignment on a subarea network which may be more detailed than the regional network.