In this study a route is defined as the path that a linear structure or facility follows in the terrain. Linear structures comprise facilities such as roads, motorways, railways, pipelines, electrical power lines, and telephone cables, each of these structures requiring specific technical parameters in what concerns the geometry of the path and having different effects on the terrain they traverse. Amongst these structures, roads and motorways are the group that creates the greatest overall impact; accordingly Portuguese legislation requires an environmental impact assessment (EIA) process as part of the necessary licensing approval. Usually the alternative (or alternatives) that undergo the EIA process is justified in terms of technical and economical issues. The result is that if major environmental impacts are identified by the EIA study, a myriad of mitigation measures are proposed, very seldom the redesign of the path being carried out (Guimarães Pereira & Antunes, 1996). Preliminary studies that precede the implementation of these types of projects are technically detailed and often come together with economical feasibility studies, shelving environmental issues for later assessment. In the methodology proposed in this chapter a multidimensional evaluation methodology, multicriteria evaluation, will be combined with the robustness of a search methodology, genetic algorithms (GAs) to generate alternative road routes that take into consideration environmental, economical, technical, and social criteria. These criteria are referenced to the physical space where the road is to be placed and therefore this methodology is embedded into a geographic information system (GIS). Genetic algorithms are particularly attractive to apply to multi-modal problems, allowing the exploration of spatial features to eventually find “best compromise” alternatives because these algorithms proceed their search by maintaining a population of solutions, that they can simultaneously exploit for their efficiency.1 Moreover, the particular mixing mechanism provides the means to recombine solutions and explore the search space. The remainder of this chapter describes evolutionary modeling of road routes, in particular the coding onto a GA of the geometric algorithm that accounts for the technical aspects of motorway siting. The details of the implementation of the MCDA-GA methodology, running within the GIS GRASS 4.1 (Geographic Resources Analysis Support System) and its application to generate and evaluate alternative routes of a section of a Portuguese complementary itinerary (IC7) will be presented.
Linkage-Based Distance Metric in the Search Space of Genetic Algorithms
