TModel Corporation has developed Multi-Point Assignment (MPA) for TMODEL2 to overcome this shortfall in most transportation models. This new module (called TM3DNA) is available to all TMODEL2 users with current maintenance for Beta test. This module is directly supported by Windows95 or WindowsNT; however, it will also operate under Windows3.1 with the addition of Win32s (available from TModel Corporation). TM3DNA operates with all of your standard files, with the addition of a Squeeze/Expand Equivalency or .ZSQ file. The .ZSQ file establishes the percentages of origins and destinations to be allocated to each loading node to be used within the zone.
There is no limit on the number of loading nodes per zone, the numbering of the loading nodes nor is there a restriction on the percentages. However, the zone centroid (the node that is numbered the same as the zone) must be accessible to all other centroids, either through being placed directly on the network or connected via a zone centroid connector. If you have used the zone centroid connector structure to develop your model, it will still work with the MPA, but you will still want to establish your .ZSQ file to specify the percentages to be assigned to each of the connectors.
The .ZSQ file can currently be developed in sections 2.3.12 or 2.7.6.3. We are building some tools that will help you automatically build and check your .ZSQ files. These tools will be included with the next update.
The TM3DNA module, with the accompanying necessary files, is on the BBS, and notification has been sent to all users with maintenance by mail. We welcome your input and questions on this module.