Optimal Routing of Road Network with Emphasis on Natural Environment Parameters According to the Least Cost Pathway Algorithm and GIS(Case Study: Delijan-Aligudarz)

Road construction is one of the most important needs of different countries. To achieve development, it is necessary to use transportation methods to transport goods and services in less time and more safety. As a result, the development and creation of new roads seem inevitable, and their construction is part of infrastructure projects that have many social, economic, political, and environmental consequences. In addition, it should be noted that the selection of unsuitable routes for construction can have potentially negative consequences for the environment of a region. These negative consequences include habitat destruction, fragmentation of wildlife populations, road accidents, floods, soil erosion, landscape degradation, and increased public access to untapped natural resources, etc. Therefore, the optimal and sustainable use of the environment in road development projects is one of the most important and fundamental stages of sustainable development in optimal routing and reducing the negative effects of the environment. The Delijan-Aligudarz route is one of the important transit roads. This road passes by the Moteh Wildlife Sanctuary, which has caused serious damages to this wildlife habitat. Therefore, environmental characteristics should be considered in the routing process to reduce damages to natural resources and achieve sustainable development goals. The purpose of this study is to choose the least costly route from an environmental and economic point of view. To achieve this goal, optimal routing and GIS have been used in this study.  

In this study, 3 groups of criteria including ecological, technical-safety, and economic-social criteria and 12 sub-criteria for optimal routing were developed. Criteria include slope, altitude, land use, geology, erosion, landslide, distance from the fault, distance from protected areas, distance from groundwater level, distance from the river, and urban and rural centers. Then the effective criteria in the GIS were digitized. Because each benchmark map has different measurement ranges and scales, the standardization process was used to standardize the measurement scales and convert them into comparable units. Criteria and constraint maps were standardized based on Fuzzy and Boolean logic, respectively. In the next stage, the AHP and WLC methods were used for weighting and integrating the criteria, respectively, and a multi-criteria evaluation map is obtained. According to this map, a friction layer was created in the GIS environment. A friction map is a raster format map in which each cell has a value that can be considered as a relative or absolute barrier to path passage. In the next step, a cumulative cost map was prepared. The cost level map shows the cost of passing from one cell to another in different directions cumulatively. Finally, the path was designed using the Least Cost Pathway Algorithm and the destination point in ArcGIS software.  

The designed and the current path were compared in terms of environmental parameters to select the path that causes less damage to the environment as the optimal path. Choosing the optimal route is a type of Multi-Criteria Decision Making. The weight of the AHP method showed that slope, distance from protected areas, and landslide sensitivity have gained the most weight, and are of the highest importance in optimal routing according to experts. The results showed that the privacy of effective environmental criteria in road construction has been observed in the designed route so that the designed route has not passed the Mooteh Wildlife Sanctuary and is more than four kilometers away, while 8.6% of the current route is located less than one kilometer from this wildlife refuge. Also, 16, 25 and 2.8% of the current route has passed through the urban, rural, and fault areas, while these environmental criteria are regarded in the designed path.  

The results show that the designed route is much better in terms of environmental criteria than the current route.As a result, it is suggested that in road construction projects, first of all, the influential factors be identified and a suitable path in terms of the environment be designed by observing the laws and principles of the environment and using GIS.