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assures that whenever a link is added, re-shaped, or a node is moved, the link length <br />will be recalculated using this scale. <br />Design Speed <br />Link speeds are entered in VISUM in miles per hour. Speeds have a direct influence on <br />the computation of travel times during simulation runs. Generally, posted speed limits <br />are entered into the program during the initial data entry phase. However, posted limits <br />do not always accurately depict the free-flow conditions on the roadway. For example, <br />some state highways have 65 mph speed limits in urban areas that are often ignored. <br />Conversely, some locations may have posted limits greater than what can be achieved <br />(e.g., arterials in fully developed areas with numerous driveways and signalized <br />intersections). <br />Speeds were entered from the NAVTEQ data and then updated with data from the <br />previous models, the data collected during other portions of this study, and during the <br />field review. <br />TWLTL <br />Links are coded with locations with Two-Way Left Tum Lanes (TWLTL). This adds 200 <br />vehicles per hour to the capacity. This should be coded for both directions of a link. <br />Link Delay Coefficients <br />Travel time on each individual link typically increases as the traffic volume on the link <br />approaches capacity. Current research has shown that the amount of travel time <br />increase depends on the functional classification of the link as well as the region and the <br />behavior of the drivers using that link. VISUM offers the ability to adjust the travel time <br />increases on the link as the volume-to-capacity (V /C) ratio changes by functional <br />classification of the link. This feature was used during the calibration process. <br />During calibration analysis, both link operating speeds and total (including both link <br />and node delays) operating speeds can be analyzed. This differential analysis is used to <br />adjust both the link and node delay coefficients. The final values used in the model <br />calibration are shown in Table 3. These values are similar to others used in central <br />Washington and are based upon experience with travel behavior in this area. The form <br />of the equation is shown as: <br />Kittitas County, Washington Transportation Model-May 2009 Page 16