Interchange Justification

The interchange justification portion of the GIS-TPT project examines the requirements for making changes to the access of the Interstate Highway System. This tool is intended to assist agency planners and engineers develop reports and the Iowa DOT in evaluating the proposed changes to the interstate system. The tools design will incorporate traffic modeling, focusing on the use of Tranplan with GIS to represent a graphical analysis of the resulting traffic characteristics on a daily basis and the Highway Capacity Software to analyze traffic levels of service on an hourly basis.

There exists policy concerning the development of additional access points to the interstate system. Under this policy, there are six required elements that must be meet to successfully defend a proposal to make changes to the access or operation of the interstate system.

     The proposed method of justifying an interchange with the interstate system will be based on either the development of a traffic model or the use of an existing traffic model and the model forecasts. The development of a new traffic model will follow the path of the model development for bypass analysis. This model will represent the initial traffic volumes and should compare closely to the existing ground counts in the area.

For both areas, the model will be modified to include the development of the interchange and the model will be routed through the processor (Tranplan) to determine the new traffic volumes that would be expected to use the interchange, if it were constructed.

For more information on either developing the model or tools that con be used to modify the existing models, click on the appropriate box.

     For both areas, their will two distinct focuses of the interchange justification. These will be a GIS analysis of the traffic model and travel patterns for the area and the use of the Highway Capacity Software (HCS) package to perform specific analysis of traffic conditions.

The information required for the GIS analysis will come from the traffic model and the data entered into the HCS will be derived from factoring the traffic model volumes. The main analysis that will be performed in GIS will be related to socio-economic characteristics around the interchange and general network travel patterns associated with the existing conditions and the changes that occur because of the interchange. The main HCS modules that will be examined in this effort are: RAMPS and FREEWAY OPERATIONS.

Select either of the analysis of interest.

Or click to examine a response to any of the six policy requirements and how this module will help address each one.

     Select any of the options to receive more information or click on the back button to return to the introduction page or the site map button to go to the site map.