Development of Prototype GIS Systems for Transportation Model Networks for FSUTMS
Network coding is a necessary and time-consuming step in travel demand modeling. The four-step demand model, on which FSUTMS is based, requires the use of TAZ, highway, and transit (if applicable) networks. In a typical demand analysis, multiple versions of these networks are created to represent the network conditions associated with different horizon years and development scenarios. Traditionally, these networks are modified individually from their respective base networks and are stored separately as individual networks. They are time-consuming to create and difficult to maintain. For example, a simple link split in a network will require that the same be done individually for all the networks affected by the split. The process is both cumbersome and prone to network inconsistencies.
The problems encountered in the traditional approach of creating and maintaining networks have led to the use of the so-called “master network” by a number of agencies from across the nation. Unlike a traditional network, a master network combines the past, present, and future networks into a single, integrated, and consistent spatiotemporal database. With such a network design, the user can generate a future network from the master network by specifying the timeline and/or scenario for which the network is to be extracted. The master network allows the users to perform all of their spatial and attribute editing in one place and avoid the need to maintain multiple and often inconsistent networks. In Florida, the Northeast Regional Planning Model (NERPM) has made use of the master network concept to maintain its networks. However, the benefit from using the NERPM master network has reportedly been offset by a significant increase in the model’s run time.
While it is clear that the Florida transportation modeling community will benefit from a more advanced master network data model, especially in the long run, the NERPM experience suggests a need for a better database design to support more efficient master network operations such as for network data storage, input, extraction, and update. In addition, the ability to extract a clean and efficient network from a master network will be key to allowing for faster FSUTMS model execution such as in path skimming and traffic assignment. The planned integration of ArcGIS in Cube Voyager will offer a robust GIS platform to develop such a network data model. However, the development of a full-fledged ArcGIS application that will meet the functional and performance needs of various networks (TAZ, highway, and transit) will be a major undertaking that will require careful studies. Equally major will be the transition from the traditional network to the master network by Florida’s various modeling agencies. It is thus important for FDOT to investigate the potential issues related to the master network concept and to develop a prototype system to demonstrate its usability and feasibility. If proved successful, the prototype system can then be developed into a full-fledged production system for adoption by Florida agencies.
This research scope will (1) review the existing master networks to identify the best practices to adopt and pitfalls to avoid in the prototype master network application; and (2) develop a prototype master network structure that can be integrated within Cube Voyager through a network “conversion” program to be developed as part of this scope. The prototype will be designed to support efficient data storage, data update, and network extraction for highway networks and to support fast model execution in FSUTMS.