Transportation network redundancy: Complementary measures and computational methods

Route Redundancy-Based Network Topology Measure of Metro Networks

“…Freckleton et al [23] defined redundancy as the ability of a traveller to adjust routes as necessary to detour around the affected sections of the network under disruptions. Actually, the concept of redundancy has been widely studied but there is no consensus definition for transportation networks, which comes down to two aspects: the number of alternatives and the network spare capacity (e.g., [10,18,24,25]). For quantifying the redundancy of transportation networks, El-Rashidy and Grant-Muller [25] proposed a redundancy index of various nodes in road networks covering the static aspect of redundancy (i.e., Journal of Advanced Transportation 3 alternative paths) and the dynamic feature of redundancy (i.e., the availability of spare capacity under different network loading and service levels).…”

“…However, the entropy concept may not be intuitive to travellers, who do care about the existence of optional routes/means. Xu et al [18] developed two network-based measures for systematically characterizing the redundancy of transportation networks: one is travel alternative diversity from travellers' perspective to address the question of "how many effective redundant alternatives are there for travellers?" and the other one is network spare capacity from planners' perspective to address the question of "how much redundant capacity does the network have?…”

“…However, in case of disruptions, the travellers' inconvenience significantly depends on the availability of alternative travel options, i.e., the amount of redundancy in the network. Yang et al [7] applied the route diversity index (i.e., the simple average number of reasonable routes between all O-D pairs) of Xu et al [18] to analyse the route diversity of the Beijing metro network and to identify the vulnerable stations. Yang et al [7] simply considered the reasonable/efficient routes in defining the route diversity.…”

“…Hence, it is necessary to have a deep understanding of the route redundancy (or route diversity) of metro networks. Following Xu et al [18], we customize the definition of route redundancy to metro networks as the number of behaviourally effective routes (or paths) available for passengers between any two stations in the metro network. The assessment of route redundancy could help to evaluate the predisaster preparedness of the current metro network or the planned scheme, and also offer the information of alternative routes to assist metro managers in rerouting passengers in a highly congested or disruptive event.…”

“…The assessment of route redundancy could help to evaluate the predisaster preparedness of the current metro network or the planned scheme, and also offer the information of alternative routes to assist metro managers in rerouting passengers in a highly congested or disruptive event. Note that this paper only focuses on the route redundancy from the travellers' perspective, i.e., the first dimension of transportation network redundancy proposed by Xu et al [18]. The second dimension (i.e., network spare capacity from the planners' perspective) of metro network redundancy will be related to the station capacity and line capacity, which itself is more complex than the first dimension.…”