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SDLs work in the VISUM model run. As traffic is loaded onto the network, the program calculates Volume-to-Capacity (V /C) ratios at each node. Intersection delay is calculated using the V/C ratio (more on how the program calculates the delay is presented in later sections of this report). If SDLs are specified at the nodes, then any delay calculated during the simulation run is assigned to the special delay link(s) approaching the node to simulate a STOP or YIELD condition. Under a four-way STOP condition, delay is experienced on all four legs and no SDLs are entered for this condition. All nodes were checked to insure that SDLs were coded where appropriate for partial way stop controlled intersections. Base Delay Additional delay, called tO in VISUM, can be added to an intersection if a known condition exists. These conditions could include an all red condition at a signal, pedestrian phases, or a node representing a railroad crossing. No additional base delays have been used in the Kittitas County model. Turn Penalty At some locations on a network it may not be possible to execute a certain turn movement or there can be a capacity constraint due to the drivers' perception of restricted sight distance or other potential safety concerns. If a movement is not allowed, then the transportation system car is removed from the turning movement layer in VISUM. Tums were restricted as necessary. At left turns at stop and signal controlled nodes, a base delay, or t0, of 6 seconds was added. These same left turns were given a capacity of 250 vehicles per hour so the tum delay would increase as the volume of the left tum increased. Node Delay Coefficients The delay caused by different types of intersection control must be defined to reproduce the delays that drivers perceive. The resultant extra travel time is dependent upon the volume-to-capacity ratio (V /C) and varies by Type of the nodes. These use the TMODEL_Nodes equation as shown in this dialog box: Kittitas County, Washington Transportation Model-May 2009 Page20