Keywords: reliability, transportation network, incident, @Risk, Monte Carlo, LHS.

One of the most important socio-economic indices of a city or a country is transportation network and its efficiency. In order to evaluate the functionality of transportation network we need to generate and evaluate the transportation network measures, such as travel time, cost, reliability and so on. But in this paper the procedure is proposed to evaluate and analyze the reliability of a transportation network. Reliability can be discussed in two ways, the first is to analyze and study the reliability of transportation components individually [roads, streets, and bridges] and the second is to evaluate the reliability of a transportation network as a whole. For the second method we prepared a three stage method. Initially, by considering the probable disaster [such as earthquakes] in the study area, some scenarios are defined. In the second stage based on network component fragility curves, supply is estimated respectively for all of the considered scenarios. Monte-Carlo Simulation and LHS can be used for these purposes. In the third stage the average travel time for each scenario is calculated and the reliability of the system is determined based on the travel time distribution. Because of stochastic entity of the stability of the component we use simulation a procedure which is fulfilled by the @Risk software program. We have simulated probability functions which describe the component behaviour in a disaster, and also simulate the desire variables such as network reliability by this program.

Various works have been performed with regard to the stability of the network components and their effects on the functionality of the whole system. These studies have been mostly related to bridges [1,2] and their related costs [3].

A methodology has been also developed for risk assessment of highway transportation systems [4] to serve as a tool in the decision process for: (i) prioritization of bridges for seismic retrofitting as a means of pre-earthquake mitigation, (ii) pre-earthquake emergency response planning, and (iii) emergency response management. Their methodology is based on vulnerability and importance assessment of the components in the system.

Du & Nicholson [5] have defined terminal reliability. It means that network centers are still connected to each other or at least there is one available path among them which can be considered as a connection. Generally after the occurrence of each disaster in a transportation system, its impacts on the transportation components have been recognized, Keller has reviewed flood disaster effects on a transportation network and has also evaluated road vulnerability & prevention methods [6]. On the other hand Sanchoz-Silva et al [7] have generated reliability models of transportation networks in order to allocate optimum resources. That is to say optimization of resource allocation increases the network reliability. Bridges are the most critical and vital components of transportation system which would break off the critical path completely if they are damaged. Moreover, the importance of these vital components will be sharply raised at the time of disaster, so stable bridges will respond reasonably to emergency activities of the disaster period.

This research represents useful method for risk analysis of vulnerable transportation networks, so that we can determine the network functionality measure. Usually, change to the process and improvement of the network functionality must be determined by the researchers in this field. For instance, Kawakami [8] has chosen the network reliability index as a measure and has analyzed the transportation network using this measure.

1

Kiremidjian, A.S. "The 1994 Northridge, CA earthquake: post-earthquake performance of transportation systems", Proceedings of the NEHRP Conference and Workshop on Research on the Northridge, California Earthquake of January 17, 1994, California Universities for Research in Earthquake Engineering [CUREe], Richmond, California, Vol. III-A, pages III-244 - III-251, 1998

2

Tanaka, S., N. Nojima, and H. Kameda. "Evaluation of Seismic Fragility for Highway Transportation Systems", Proc. of the 12th World Conference on Earthquake Engineering, New Zealand, 2000

3

Werner, S.D., C.E. Taylor, and J.E. Moore II. "Loss Estimation Due to Seismic Risks to Highway Systems", Earthquake Spectra, Vol.13, No.4, pp585-604, 1997. doi:10.1193/1.1585970

4

Basoz, N. and A.S. Kiremidjian "Risk assessment for highway transportation systems", Proceedings of the Sixth U.S. National Conference on Earthquake Engineering, Earthquake Engineering Research Institute, Oakland, California, 1998.

5

Nicholson, A., Z. Du.,"Degradable Transportation System: An Integrated Equilibrium Model", Transportation Research Board, Vol. 31, No. 3, pp 209-223 1997. doi:10.1016/S0191-2615(96)00022-7

6

Keller, C., "Rural Road Vulnerability Reduction Assessment, Mitigation Measures, and Training", Natural Hazard Review, Vol. 3, No. 4, 2002. doi:10.1061/(ASCE)1527-6988(2002)3:4(139)

7

Sanchez-Silva. M., M. Daniels., "A Transport Network Reliability Model for the Efficient Assignment of Resources", Transportation Research Part B, Vol. 40, pp 342-353, 2004. doi:10.1016/j.trb.2004.03.002

8

Kawakami, H., "Reliability Analysis of Urban Transportation System", Proc. of the 12th World Conference on Earthquake Engineering, New Zealand, 2000.

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