A methodology to identify unreliable links in a road network after earthquake (Case study: Tehran City Network)

In this study, in order to identify vulnerable links, the performance of the network due to the obstruction of each link is evaluated by considering the simultaneous effects of supply and demand and assuming that drivers are aware of the obstruction status during the trip. Accordingly, by considering a specific routing pattern by users, the performance of the network is evaluated in the case of blockage of that link, and links whose removal does not lead to unacceptable changes in the network versus non-blocking, are considered as reliable links. In the following, it was implemented in the Tehran network based on 0.35 percent as acceptable changes. This value is equal to the minimum value of acceptable performance changes which makes it possible to access all points to evacuation destinations using the remaining reliable links. The basis for access will also be the possibility of creating an access tree. According to the evaluation of network performance due to the blocking of each link in EMME2 software and its comparison with the acceptable limit, 17.3% of the links of Tehran network will be unreliable links as a result of a possible earthquake. The most unreliable links of the network are observed in arterial roads, especially in the CBD. Therefore, although the removal of vulnerable links with arterial type can increase the reliability of the evacuation network by other existing links in terms of continuity and travel time, but this is due to the role and importance of this road type in network integrity and network efficiency, will lead to disruption of the network evacuation capacity. It makes necessary to development of parts of the network in the form of widening or adding links to the network in order to provide the required evacuation capacity. Obviously, if this is not possible or it is costly, especially in areas with dense texture, solutions such as retrofitting buildings as much as possible can be put on the agenda to reduce the demand for evacuation.