Proposing a Quick Seismic Risk Evaluation Method for Inter-city Road Systems

The intercity road systems are of essential use for rescue and relief, aid delivery, temporary settlement and reconstruction purposes in the aftermath of major earthquakes. The lack of efficiency of Kerman-Bam road because of Bam earthquake of 2003 and the complete blockage of Chaloos road for a long time because of Firoozabad Kojoor (Baladah or Kandovan) earthquake of 2004 are just two samples which show the vital role of intercity road systems in increasing the casualty level and indirect losses of earthquakes. Therefore, seismic risk evaluation and reduction for these systems is of very great importance, especially for those countries, such as Iran, which do not have enough equipment and infrastructures and are suffering form lack of widely spread reliable transportation networks. In spite of this importance very few studies have been performed on the risk evaluation and reduction of intercity roads, and the available publications in this regard are mainly focused on the highway systems.It should be noted that there are two major differences between intercity road systems and the other lifelines: 1) the possibility of complete blockage of the road because of extensive damage to either the road body (the embankment), or landslide in trenches, or the road’s key structural components such as bridges, tunnels and culverts, while other lifeline systems are not usually totally interrupted, and can benefit from the existing redundancy, and 2) decision-making possibility of the people who are transferred by the road, as a lifeline, in the contrary to other lifelines which transfer a lifeless product such as oil, gas, or water. The decision-making possibility makes the risk evaluation and mitigation of the road system much more complicated. In this paper at first these differences and their effect on the risk management process have been thoroughly discussed, and then a risk management model has been introduced in which on the one hand all features on which the importance of a road in the transportation system of a county depends, including the capacity of passenger and cargo transfer in different seasons of the year, its classification, its service area, and so on, and on the other hand, all parameters which affect the road function in the aftermath of a major earthquake, including its vulnerability level, its geographical situation, and the possible redundancy, have been taken into consideration. The proposed risk management model is engaged with: a) complete and overall studies on two main parts of each road, namely road body and its structural components, b) definition of time- and user-dependent earthquake scenarios, and c) evaluation of earthquake economic direct and indirect losses. The proposed model have been applied to Iran intercity road system and a prioritization scheme has been suggest on this basis, which can be used by the authorities for budget assignment to various provinces of the country for upgrading the road system. A somehow new concept, which is used in this study, is “the road service area” which is defined based on a major origin-destination pair and their surrounding industrial, cultural centers, or the centers of any type of economic activity. By using this concept, each country cab be divided into some “road service areas” and then these areas can be prioritized based on various parameters, including hazard, vulnerability, and the transportation service presented in each area. For this purpose each parameter is given a weight factor and then by combining all contributing parameters with their associated weights an importance ratio can be calculated for each “service area” based on which the prioritization can be performed.The proposed “Quick Risk Assessment Method” has been applied to Iran road system, however, as the “service areas” have not been defined yet for roads in Iran, the provincial divisions have been used instead, and a table showing the prioritization factor of various provinces has been presented which can be used for making decision on the provinces which should be studied more in detail, and also for budget assignment for seismic upgrading of roads in various provinces. The main advantage of the proposed method is its simplicity. Furthermore, it is possible to add as many as desired parameters to the model without any difficulty, provided that the weight factor of that parameter can be given on a reasonable basis.