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The Modeling Process <br />A transportation planning model is constructed with the purposes of forecasting traffic <br />and operating conditions. The model is first calibrated to replicate existing or base-year <br />travel patterns. The model inputs are then modified to represent future conditions, <br />making it possible to project traffic volumes. This gives transportation planners and <br />engineers the ability to determine the impact of different roadway or land use scenarios <br />on the traffic network. This, in tum, allows the professional to evaluate economic <br />decisions on potential capital improvements and then make appropriate plans. One <br />such use of these models is to test several forecast conditions. <br />Model Area Identification <br />The modeling process begins by determining the area to be modeled. The Kittitas <br />County model includes major roadway facilities within the Kittitas County boundaries, <br />including all cities. When the county model was developed, detail within the City of <br />Ellensburg and to some extent within the Cle Elum area was included so that the model <br />could be later refined for use by the cities. Because the model was developed with the <br />NAVTEQ data set as its basis, the model also includes rail and trail transportation links <br />and other points of interest such as rivers and lakes. The model area with traffic <br />analysis zone boundaries is shown in Fi ur · 1. <br />Figure 1 -Model Area with T AZ Structure <br />Kittitas County, Washing ton Transportation Model -M a y 2009 Page 3