NE T WORK ANALYS I S GIBSONTON AREA 2. ANALYSIS METHODOLOGY
area. This was done so the recommended alternatives developed for the Lithia-Pinecrest area could be seamlessly integrated into the Gibsonton study area analysis, with no rework needed. The original model was developed by running the Tampa Bay Regional Planning Model (TBRPM v8.2) using Cube software. (Note: This version was used because TBRPM v9.0 was not available when the analysis was initiated.) Cube output includes link and node shapefiles and OD matrices. The link and node shapefiles are imported into Aimsun. This allows the Aimsun model to use the same basic roadway network, roadway attributes, centroid, and OD data as the TBRPM. Using a larger model area (see Figure 3) impacts the results to and potential impacts within a larger network than modeling just within the Gibsonton Study Area. 2. Run a macroscopic Aimsun model and compare volume results to the Cube output. If the R2 value (a statistical measure of variance) is at least 0.90, the subarea network was created. A similar R2 comparison was performed for the subarea. 3. Once the modeling limits were selected, Hillsborough County provided traffic counts, signal timings, and funded or committed projects within the study area. Calibrate the model by adjusting section and turn parameters to make the AM and PM Aimsun volumes match the count data. When the majority of turning movement volumes matched between these two sources, the OD matrices and path assignments were finalized. These OD matrices and paths became the starting point for all alternative set models. However, intersection turning movement volumes may vary between models, due to the dynamic nature of the Aimsun model. 4. Update intersection and roadway geometries, along with intersection control types, to create an Existing plus Committed (E+C) Model, which was used as the starting point for all the alternative sets that were analyzed.
The alternatives analysis process included several steps to compare the network performance of improvement options within the Gibsonton area. The analysis used Aimsun simulation and forecasting software calibrated to represent existing traffic conditions using existing regional traffic model data, intersection traffic counts, and signal timings. Aimsun is a unique software because of its ability to analyze the performance of roadway networks under existing or potential improvements. Analysis can be performed at either the large-scale regional level or smaller intersection and corridor level. The Aimsun software allows multiple projects to be added or removed depending on the alternative to be tested. These tests can be performed and results processed and evaluated quickly. The benefit of Aimsun for this type of study is that it combines two scales of modeling, regional model inputs (macroscopic) with intersection or corridor model inputs (microscopic), to create a hybrid model (mesoscopic) that offers a variety of analysis techniques. Aimsun macroscopic modeling operates similar to Cube modeling, utilizing Origin-Destination (OD) matrices and link parameters in determining routing information. Aimsun microsimulation operates similar to Vissim microsimulation, utilizing traffic control features and car-following and lane changing models. These models allow for interaction between vehicles and can show model animation. Mesoscopic modeling, or hybrid models, combines the individual vehicle modeling found in microsimulation with the higher level, regional modeling performed in macrosimulation. As described below and summarized in Figure 2, the study team employed the following process to complete the modeling effort: 1. Use the model developed for the Alternatives to Lithia-Pinecrest Road Widening Traffic Analysis Study as the base model for the Gibsonton
Summary Report
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