Hands On Model Networks Web page (www.esri.com/news/arcuser/avmodel.html). These Hands On articles build skills. If you want to model individual turn penalties for many or all intersections, you can create individual rules for all intersections. This is a complex procedure that I do not recommend for people who are new to working with networks. Dont Give Up Stay with it. As you refine your network, you will be amazed with the possibilities. Building a reliable time-based network is not an easy task, and tuning and maintaining it are even tougher. Do not be discouraged. There are probably many potential partners in and around your jurisdiction that might want to help. In addition to finding some help in creating and maintaining your network data, here are some strategies for making the job easier. J Start Small Directionality Travel direction is critical when modeling one-way travel on divided highways, boulevards, one-way streets, and even individual travel lanes. When streets are digitized, the digitizing direction creates an underlying street direction. To manage travel along or against this direction, a twocharacter text field named One_Way provides an effective way to flag travel direction relative to digitizing. Simple FT (from-to) and TF (tofrom) codes define the course along and against the digitized direction. To check directionality against digitized direction, place small arrows at the terminating end of the street segment. Code a selected segment FT if travel is along the elements direction; use TF if travel opposes. In an edit session, also watch for the segment's red endpoint; it also represents the terminating end. If your street network will not support address geocoding, you may also flip the street direction to reflect actual travel. Again, check out "Do It Yourself—Building a network dataset from local agency data" to learn this workflow. If you do use streets for geocoding, you may still reverse its direction, but you must reassign the left/right to/from values to respect the new orientation. This difficult task requires attention to detail, and I do not recommend it for beginners. When you build a network dataset, Network Analyst will recognize the One_Way field and create the appropriate rules. When using the network, you will have the option to globally turn the One Way property on or off. Turns and Turn Relationships In a time-based network, turns and intersection slowdowns are very important. Global turns may be quickly applied throughout a network. As you build your network, use actual field times to calibrate them throughout your jurisdiction. You will probably find that travel times under constant low volume will vary slightly throughout your area. Experiment with global turns to achieve a best average. Field testing is described in "Convincing the Chief—Proving that time-based networks really work," an article that appeared in the Spring 2009 issue of ArcUser and that is also available from the Network Modeling, Learn How to www.esri.com Build a small network in an area that you know well. Experiment and tune it to match field tests. Carefully watch how the network behaves as you build small service areas and test routes. If impedance, connectivity, geometry, and travel direction misbehave, practice fixing and rebuilding them. Test, and test, and test! J Think Big Ultimately, your network will probably support the response efforts of many jurisdictions. Talk to your neighboring jurisdictions and develop partnerships. Collectively decide to obtain/create and maintain just one network dataset. J Keep Both Eyes Wide Open Continually monitor your network's behavior. Repair problems individually or in small groups. Rebuild and retest problem areas. Do not be discouraged if fixing one problem just reveals another. J Document Your Work Develop a method to track edits and network builds, especially when adding new segments and modifying attributes. When you build the network for the first time, before you click the Finish button, save your parameter summary to a text file with a date stamp. If you ever have to present and defend your work, you will be glad you did. I have presented network models to the legal community, and this information is priceless. J Back Up and Try Again Occasionally, a network dataset becomes quirky or even corrupt. Do not hesitate to delete the problem set and rebuild using the same parameters. If you use a standard naming convention, you might be able to reuse the same dataset in an existing ArcMap document. Be very careful with this, though. You might have to remove the repaired dataset from an existing ArcMap document and rebuild all the solvers. I have had mixed success with replaced datasets and consider the jury to still be out on this strategy. ArcUser