Differences in Network Reliability Improvement by Several Importance Indices

For constructing a highly reliable highway network under a disaster environment, this paper presents a comparative study of the importance indices and proposes an approximate method for improving highway network reliability. Three indices are compared. Two of them are conventional indices of reliability importance (RI) and criticality importance (CI), and the other is the improved criticality importance (CIW) index recently proposed by Wakabayashi (2004). First, the significance of reliability importance is discussed. Second, their definitions, merits, and demerits are explained. Third, several cost functions for improving link reliability are introduced. Fourth, RI and CIW are compared for a small-sized network and differences in improved link reliability are discussed. Fifth, an approximate method is proposed using partial minimal path sets. Lastly, after calculation experiments, the advantages of the CIW index and the effectiveness of the proposed approximate method are demonstrated.