Exploring the use of GIS-based Least-cost Corridors for Designing Alternative Highway Alignments

Sammanfattning: Finding an optimal route for a new highway alignment is a task which requires a lot of resources. In the planning phase, choosing the location of a new highway alignment is very important as it will heavily affect the total construction cost. However, the perfect location of a new highway alignment is ambiguous depending on many parameters. The objective of this study is to explore the use of Geographical Information Systems when designing candidate locations, in the planning phase of the construction, of new highway alignments. This will be executed by finding least-cost corridors in a raster space known as a cost map based on stated criteria. The least-cost corridors are calculated using a Least-Cost Corridor algorithm (Shirabe, 2015) and will represent an area of the optimal location. The study is based on calculations performed in an area containing parts of the E4-highway in Jönköping, Sweden. The study area is approximately 50,000 hectares, containing features such as water bodies, urban areas, fields, forests, hills and more. Lantmäteriet provides the datasets available at the Swedish University of Agricultural Sciences. All feature layers are converted to raster in ArcMap, which allows the use of ArcGIS Spatial Analyst tools and to assign values to different fields in a layer. Due to limitations of the algorithm, the study area is divided into two sections and the raster layers are aggregated from a cell size of 2 meters to a cell size of 20 meters. By assigning scoring to the different feature layers, and allocation of criterion weights between the layers, cost criteria maps will be calculated. Three cost maps are calculated with three different allocations using Analytical Hierarchy Process (AHP). Finally, to generate the optimal candidate highway alignments using the algorithm, the corridor width is set to 400 meters which is 20 pixels in the raster space. In conclusion, what we found is that GIS works well as a tool for the purpose of designing candidate locations of alternative routes of existing highways. However, the results are suggestive which means that the computer cannot be left alone to choose a final alignment. Instead, it facilitates the work and perfects a problem based on human conceptualizations of the real world. The limitations of GIS for this purpose is mainly the cost assessment and allocation of weights between criteria. It is difficult to establish the significance of one layer to another since all criteria do not have an actual cost. It is important to note that any weights will be subjective, further reinforcing GIS as a means for getting suggestive results for highway alignment problems.