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generate traffic. For the previous modeling efforts, Kittitas County supplied a TAZ <br />system that was developed previously by county staff. For the 2008 Kittitas model, the <br />TAZ system was reviewed and revised. Traffic Analysis Zones were subdivided in <br />growth areas and other locations to match the detail of the network. The TAZ system <br />used for the model was shown in Figure 1. <br />Two types of zones were used: internal and external. Internal zones can consist of a single <br />parcel, a group of like land uses, or a gathering of local land uses separated by natural, <br />physical, or political boundaries. Several factors are considered to find the best zonal <br />design. The primary factor is related to the results expected of the model. It may be <br />logical to place the zone in a way that groups all land uses bounded by network <br />roadways. The second factor is how the available land use information is <br />geographically described. Because the land use data was derived from the Kittitas <br />County parcel layer, the TAZ structure could be defined to best match the <br />transportation system. The Kittitas County model now consists of 300 internal zones. <br />External zones account for all vehicle trips that enter and leave the model area. <br />Depending upon the desired results, it may be logical to place an external zone on each <br />roadway that leaves the network. In other cases, local traffic conditions may establish a <br />need to tie together several exiting roadways into a single zone so that the external <br />destination of the trip can be simulated. For the Kittitas County model, it was decided <br />that the external zones would be placed at the following locations: <br />External <br />Zone <br />Location <br />1000 <br />I-90 West <br />1001 <br />SR 97 North <br />1002 <br />I-90 East <br />1003 <br />I-82 South <br />1004 <br />SR -821 South <br />Data Collection and Coding <br />After the model area has been identified, the collection and entry of the necessary data <br />to run the modeling program begins. There are two primary components to be entered: <br />network and travel characteristics. The network data includes: roadway (link), <br />intersection (node), turn movement penalty, link delay functions, and node delay <br />Kittitas County, Washington Transportation Model - May 2009 Page 5 <br />