Modify the Existing Network

The first step of developing the interchange justification is to modify the original Tranplan network to represent the new interchange. As stated previously, this operation can be accomplished through the use of HNIS, modifying text files or through the GIS-Tranplan interface. This documentation will focus on the use of the GIS-Tranplan interface.

We start by examining our existing network with MapInfo GIS.



Zooming the area of the proposed interchange, we see that although there is a node at the intersection location, this node is only to represent a turn in the network - not an interchange.



For this example, we will assume that all possible alternatives to avoid placement of the interchange have been ruled unfeasible and that this location represents the best possible interchange location.

The process of modifying the network to represent the interchange involves editing the nodes and links table for the network. The user then needs to digitize new nodes and links to represent the desired location and structure for the interchange. In the example, the user needs to only change one end of the north-south link to meet the interchange node and place a new link from the interchange node to the end that was moved. After doing this step, the program BYPASS.MBX should be run to develop the new node numbers, lengths, and assign default speeds and capacities. The user should then change the default speeds and capacities if desired, save the modified network tables and perform a run of the Tranplan modeling package (with or without the modification to load selected links or build selected trip tables).

The modified network is shown in the following figure.



After modifying the network to represent the interchange, the user should examine the new volumes in the GIS environment. One tools for examining the differences in volumes is through the comparison plot technique develop in MapInfo. This capability provides band-width displays of differences in traffic volumes between model scenarios.



If other GIS-based visualization of the 24-hour volumes are desired, please examine the sections on loading selected links and building selected trip tables.

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