Geo-environmental assessment to identify a least-cost road in Ghana

Unlike many studies which simply generate least-cost paths, this paper develops a geospatial methodology for amalgamating many geo-environmental factors in order to determine the costs of construction for pre-defined or existing roads. The geo-environmental factors used were elevation, presence of watercourses, soil characteristics and land cover type. They were reclassified to cost values/attribute weights based upon their impact on road construction, and they were then combined, using the weighted overlay tool in ArcMap, to generate a thematic cost layer. The total construction cost for each road was then extracted from this layer using the Extract by Mask tool. Although the cheapest road was longer, it was less costly by 3.2%, mainly because of its higher elevation, avoidance of major valleys, suitable soils and less problematic land cover, all of which reduced the need for cut-and-fill and culverts. It is suggested, therefore, that government agencies adopt this powerful technique for reliable and well integrated road planning and assessment. Nevertheless, the method could be improved by including additional factors such as proneness to floods and access to people and socio-economic activities.