The values contained in each layer are multiplied by the weighting factors and then added together. The Fig. 2 map shows the relative cost value at each location in the study area. As with calibrating the layers, the public can help identify relative weights between the various layers, which may improve the acceptability of the final route selection.

During the next step, the model will be used to develop an accumulated cost map from the start or termination point for the route (for example, a substation or transmission line tap). The program calculates values for each grid within a project area using a propagating wave, which incurs the average cost identified for each pixel within the project area and concurrently increases with the distance from the endpoint. The resulting map shows the lowest cost of accessing every location within the project area from that endpoint.

Finally, the model then identifies a route or corridor through the accumulated cost map of the previous step by locating the “least cost path” from one endpoint to another. Figure 3 depicts the computer-generated path that represents the lowest cost route through the roads, sensitive areas and houses identified previously. Sometimes a route identified by the computer can be circuitous, which is not usually ideal for a transmission line. It may be preferable to identify a corridor using the model within which the routing specialist may then identify a more specific alignment. This process also can be used to compare impacts for different routes identified by either the grid-based or traditional routing methods.

Because we live in a 3-D world, it is often more intuitive and informative to the public if they can see what a transmission line will look like in 3-D, in addition to seeing the typical 2-D map overview of the proposed routes. Elevation data is the foundation of 3-D displays, but any point, line or polygon attribute can be extruded to form a 3-D map. Points become lines, lines become vertical surfaces and polygons become volumes when stretched into 3-D.

Many tools are now available that can make preparing photo simulations and 3-D renderings fast and easy. Almost everyone is now familiar with Google Earth, a free web-based program that allows its users to spin the earth, zoom in or out, fly through an area and change the viewing angles of the earth. Likewise, the ArcGIS suite of applications contains ArcGlobe and ArcScene and functions much like Google Earth. All of these applications have the benefit of integrating with project data generated from ArcMap. Both of these programs operate on a rapid retrieval and display system that allows fast rendering of large volumes of data.

The ArcScene program may be primarily used for the visual simulations of a project or particular area. Not only can it create realistic-looking static simulations, but it also has several animations that enable it to create more dynamic simulations. The camera animation allows the user to create a “fly-through” that can show what a new line might look like from a variety of viewpoints or the overall view of the entire route. Layer and scene animations allow the user to animate the application of different layers, such as homes or roads, or create visuals showing different seasons or weather.

In addition to these programs, a variety of other programs are available that can create or enhance visual simulations or animations, such as PLS-CADD and other third-party programs that may provide more realistic trees or structures.

Technology has improved the transmission line routing process, from the collection of data to developing routes and beyond, into the public and regulatory approval processes. While most of these programs and techniques have been around awhile, they will likely become more commonly used and more effective as digital data becomes more readily available, and as computer processors continue to get faster. Just 10 years ago, most personal computers could not have handled the computational demands of these programs, but today there are fewer limitations on the programs that can be run from individual computers.

As these technologies continue to evolve, it is still up to the routing specialist to evaluate whether they will provide a benefit to each project. In some cases, the cost of implementing these programs may outweigh the benefits, especially for projects in rural areas where there may be few constraints or where little opposition is expected. For high-profile transmission line projects, however, using these technologies may help the public and regulators better understand the potential impacts of the alternatives and the decision-making process that was used to identify the preferred transmission line route.

Kristi Wise is a project manager in the Environmental Studies & Permitting Division at Burns & McDonnell (Kansas City, Missouri, U.S.). Wise has investigated social, environmental and engineering constraints, and prepared public involvement programs for numerous transmission line routing projects, spanning more than 2000 miles (3219 km) in 12 states. Wise is currently involved in 100-kV, 230-kV and 345-kV transmission line projects in North Carolina, Virginia and Kansas. kwise@burnsmcd.com