Seismic Vulnerability Analysis of Urban Roads Network

While risk reduction has been mainly addressed by seismologists and engineers by now, the total impact of earthquake greatly depends on urban planning factors. The effects of planning can be considered in the socio economic and physical aspects. Urban planning may have a dominant role in various earthquake phases: at the time of earthquake; rescue, and emergency, as well as temporary and permanent settlements. There is a strong relationship between the level of planning and the effects of a disaster on the community. Urban planning with the purpose of vulnerability reduction has to recognize vulnerability causes for every physical city elements. Seismic pathology of communication networks, especially urban roads, as one of the main physical elements of city, is a key issue. Initially, urban roads should play key roles in the provision of access to suitable open spaces and escape. The main purpose of this research is to analysis and recognize the factors affecting urban roads vulnerability and to determine their effects. In the context of urban planning criteria, special criteria are selected for evaluation of urban roads vulnerability. In this process, AHP (Analytical Hierarchy Process) method, as well as GIS, SPSS and Export Choice software were utilized. As the case study of the research, Karmandan neighborhood, located in the central established area of Karaj City, some 30 kilometers west of Tehran, the capital, was selected. Some information and data were collected through existed and approved plans for the case study area. However, the main data were collected through field survey, conducted during the research in the city of Karaj. Using previous research and studies, 10 criteria were selected for evaluation the roads vulnerability, including: 1-hierarchical accessibility; 2-degree of roads enclosure; 3-the quality of roads wall; 4 type of roads (dead end or open end); 5 material types used in roads; 6 land use of allotments located in roads; 7-the gradient of roads; 8-location and characteristics of urban infrastructures; 9-internal angle of roads; and 10-population density related to roads. The findings of the research showed that three criteria are the premier factors affecting vulnerability of urban roads, including population density related to urban roads network, the location and characteristics of urban infrastructures, and the gradient of roads. Two other criteria are less important, including hierarchical accessibility and internal angle of roads. The results of correlation analysis showed that it is not possible to determine the level of threshold for the mentioned scales. The reasons for this are: correlation among scales, data overlapping and direct and reverse effects of scales on each other, and seismic vulnerability of urban roads. Vulnerability of urban roads is not the effect of one factor, but it is the consequence of various factors. It seems that the model introduced by this research, benefiting from simultaneously analyzed criteria and factors, can be a fair and efficient method for evaluation of the vulnerability of urban roads. By using this method, priorities may be determined in action plans to prevent seismic vulnerability, as well as pre implementation evaluation in new urban development projects.