Convincing the Chief Proving that time-based networks really work By Mike Price, Entrada/San Juan, Inc. Many recent ArcUser articles have shown how to design, build, and run time- and distancebased travel networks for emergency response modeling. These model posted or customized speeds, global turn rules, and slope corrections. Previous articles assumed that the modeling parameters and analytical findings were correct. This tutorial uses data from Fire District (FD) 37 in South King County, Washington, and re-creates two analyses that were recently performed by agency staff to validate the district's time-based network travel model. The ArcGIS Network Analyst extension's OD (Origin-Destination) Cost Matrix will be used to test and validate actual timed trial runs for several stations. Previous tutorials that appeared in the July­September 2007, October­December 2007, and Summer 2008 issues of ArcUser can be used to review the ArcGIS Network Analyst modeling method and the concepts of distribution and concentration. These articles provide more information on how emergency responders use time as a response measure. Getting Started To begin the exercise, visit the ArcUser Online Web site at www.esri.com/arcuser and download the sample dataset for this tutorial. This is the fourth in a series using Fire District 37 data, so the parent folder is named FD37_4. 1. Unzip the archived sample dataset at or near the root directory of a local drive. The archive creates a folder called FD37_4. 2. Open ArcCatalog and explore the data in FD37_4. Notice that there are three subfolders named DBFFiles, SHPFiles, and Utility. All exercise data is registered in Washington State Plane NAD83 North Zone U.S. Feet (WASP83NF). 3. Inside SHPFiles, notice the WASP83NF folder. This shapefile subfolder contains several shapefiles and layer files that will be used in this exercise. 50 ArcUser Spring 2009 4. Inspect the DBFFiles folder and see that Time_Runs_1 contains run data for four FD 37 fire stations, recorded at four- and eight-minute travel points. 5. Open RunSummary1.xls and see that it contains one worksheet, Statistical Summaries, that is ready to tabulate statistics for the four- and eight-minute runs for each station. 6. Leave ArcCatalog open. To gather data for this project, station duty crews at each station were instructed to drive 10 different routes from their station to locations on the street network. They drove the routes at speeds at or near accepted response speeds, in light to moderate daytime traffic, and in good weather. The apparatus officer noted the exact location of the four-minute and eight-minute time point on each route. These time points were then mapped and are available for this exercise as a dBASE table including WASP83NF coordinates. Building a Network Dataset with Network Analyst 9.3 In ArcCatalog, verify that the Network Analyst extension is available and active. 1. Navigate to FD37_4/SHPFiles/ WASP83NF and locate streets_nw.shp. Preview the attribute table for this layer. Notice that it contains network-ready data including fields for a time cost in minutes, length in miles, and one-way flags. These fields will be used to build a network dataset. 2. In the Catalog tree, right-click streets_ nw.shp and select New Network Dataset. Accept the default name and click Next. 3. Inspect Connectivity and accept End Point as the only connector; click Next. The streets use geometry rather than elevation to define crossing relationships, so do not modify connectivity. 4. Click Next and accept Global Turns; click Next again. 5. In the network attributes window, click the Add button to add an attribute. In the new Add New Attribute dialog box, type Length_Mi for Attribute, choose Cost for Usage Type, choose Miles for Units, and leave Data Type as Double. Notice that Minutes and Oneway are both default parameters because the primary test will be fastest travel time, not the shortest distance. 6. Highlight Minutes and click the Evaluators button. In the Evaluators dialog box, select the Default Values tab. For the Turn element, click on the word Constant to see four options. These options now include a new one in ArcGIS 9.3 called Global Turn Delay. Select this option and press F12. 7. A new Global Turn Delay Evaluator appears. Notice that this evaluator supplies defaults but allows modification of the intersection approach angles and the delay times. Also notice, that feature classes can be used to create complex relationships between different street classes. 8. Save the map document. The streets in this sample dataset are rather simple and will only require the use of one Local class. The Seconds field in this dialog box accepts values for delays for straight travel (with and without crossing roads), right and left turns, and U-turns. After tuning the streets in the sample dataset, it was determined that the delays shown in Table 1 work best throughout the district. www.esri.com