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and other land use in the area. These inventories, along with model "rules" are used to <br />generate traffic volumes for all roadways within the model. These forecast volumes are <br />compared with current traffic counts. When the model matches the traffic counts within <br />acceptable ranges of error, the model can then be used to test future year scenarios. <br />These scenarios may be changes in number of housing units, employment quantities, <br />travel behavior patterns, or roadway improvements. The transportation planner, using <br />the transportation planning model, can project future traffic volumes without the cost of <br />building inappropriate roadways or waiting for traffic congestion to severely impact <br />travelers. <br />The 2008.Kittitas County model was developed with version 10.03+ of VISUM, part of <br />the PTV Vision Suite of software. Most importantly, this version of the model was <br />updated in 2009 with updated base year land use inventory and forecasts supplied by <br />Kittitas County, new traffic count data supplied by Kittitas County and the City of <br />Ellensburg. This update included review of the network and forecasts involving Kittitas <br />County staff. <br />This document describes the methodology that PTV America, Inc. (PTV) and Kittitas <br />County staff used to develop the model. Because modeling is a complex process, much <br />of the theory, terminology, and concepts are also discussed. <br />Kittitas County, Washington Transportation Model - May 2009 Page 2 <br />