Transportation security and the role of resilience: A foundation for operational metrics

This paper presents operational metrics to determine a passenger transportation system's resilience to terrorism. The metrics range from those specific to the number of trips to more holistic measures that include the contribution of these trips directly and indirectly to economic activity. These metrics can aid decision-makers in rendering more informed judgments about resource allocation and how to design a portfolio of security and recovery strategies.The paper also provides a framework for evaluating transportation risk, including the important role of perceptions in potentially amplifying these risks. It provides a range of strategies to promote resilience as well. Resilience of a transportation system is then quantified using the real-world case of the 2005 London subway and bus bombings. In terms of ordinary resilience, we find that 77.4 percent of total journey reductions on attacked modes were offset by increases in substitute modes for the 4 months following the attacks. We also estimate that 76.9 percent of total journey reductions on attacked modes were the result of a “fear factor,” as opposed to capacity reductions.The paper concludes with a set of proposed prospective resilience measures to evaluate the potential resilience of a transportation system. These metrics are based on the vulnerability, flexibility, and resource availability to cope with a terrorist attack or natural disaster.     

Measures to evaluate post-disaster trip resilience on road networks

The resilience of transportation networks, one of the most critical infrastructure in post-disaster situations, will have a significant influence on post-disaster operations, community resilience and business continuity. Consequently, understanding the resilience of transportation networks following a natural disaster is crucial. This research proposes a new Trip Resilience (TR) measure to assess the resilience of trips on road networks following a disaster, integrating all three dimensions of resilience, namely robustness, redundancy, and recovery. The methodological approach includes an analysis of existing transport resilience measures presented in the literature to assess their ability to quantify robustness, redundancy and recovery in terms of the proposed conceptual model. The analytical formulations of the individual component measures are then developed, or adapted from previous research, along with a means of integrating all three into a combined Trip Resilience (TR) measure. A case study methodological approach is then adopted to verify the practicality of the proposed measures using the outcomes from a transportation simulation of a hypothetical Alpine Fault Magnitude 8 (AF8) scenario. A Normalised Trip Resilience (NTR) measure is also proposed that converts the TR to a normalised scale that is easily understandable to decision-makers. Finally, in order to facilitate ranking of the post-disaster impact on districts, a new measure, namely the Equivalent daily number of Impacted Trips (EIT), is proposed. The proposed measure provides an opportunity for decision-makers to estimate and rank the trip resilience between each (group of) Origin-Destination pair(s) using pre- and post-disaster flow and travel time. The resulting measures were capable of being calculated from the outputs produced by the transportation simulation model in the case study, thereby verifying their practicality in real-world situations. The importance of including both robustness (represented by the number of eliminated trips) and redundancy (represented by increased travel time), over the horizon of the post-disaster recovery phase was highlighted. Eliminated trips contributed significantly in areas that were cut off and isolated post-disaster, due to a lack of alternative routes, and increased travel time contributed as more roads were reopened but the alternative routes resulted in increased travel distances and, consequently, travel time.     

Importance measures for inland waterway network resilience

This work demonstrates a time-dependent paradigm for resilience and associated stochastic metrics in a waterway transportation context. We deploy two stochastic resilience-based component importance measures that highlight the critical waterway links that contribute to waterway network resilience and develop an optimization approach that determines the order in which disrupted links should be recovered for improved resilience. A data-driven case study illustrates these metrics to describe commodity flows along the various links of the US Mississippi River Navigation System.     

Impact of transalpine rail network disruptions: A study of the Brenner Pass

This work investigates the impact of sudden rail closures on transportation networks and the local industries affected. A decision support system is introduced, which automatically generates a rail network and simulates passenger and freight traffic. In case of rail closures, freight traffic is rerouted and resulting delays are calculated. Furthermore, the option to transship from rail to road at terminals is enabled. The model is tested using data originating from a major transalpine rail corridor, the ‘Brenner Pass’, which connects Austria and Italy. Results show rail links which are critical and the impact of various disaster scenarios is compared.     

Evolution of the international air transportation country network from 2002 to 2013

In this research, we analyze the evolution of the international air transportation country network from 2002 to 2013 with two perspectives: The network’s physical topology and the functional network with traffic information. Our analysis shows that the network is scale-free and has the small-world property. The evolution of triadic properties suggests that the network gears towards symmetric, transitive closure. We find that United States, Great Britain, and France are critical from both perspectives; Surprisingly, South Africa is particularly critical from topological point of view. Furthermore, topological and functional criticality are highly correlated to the GDP of a country.     

A three-level supply chain network design model with risk-pooling and lead times

This paper considers a single-sourcing network design problem for a three-level supply chain consisting of suppliers, distribution centers (DC’s) and retailers, where risk-pooling strategy and DC-to-supplier dependent lead times are considered. The objective is to determine the number and locations of suppliers and DC’s, the assignment of each location-fixed DC to a supplier and that of each retailer to a DC, which minimizes the system-wide location, transportation, and inventory costs. The problem is formulated as a nonlinear integer programming model, for which a two-phase heuristic solution algorithm is derived based on the Lagrangian relaxation approach. Numerical experiments show that the proposed heuristic is effective and also efficient.     

Long haul freight network design using shipper–carrier freight flow prediction: A California network improvement case study

Transportation network design is a method for analyzing the interactive benefits of transportation projects applied to a network. In this paper, a network design model is developed for long haul freight movements which are represented by relationships between shippers and carriers. Additionally, an explicit capacity constraint is used to divert traffic volume from congested links. A case study based on the California transportation network is implemented to examine the effectiveness of this model when applied to a large network. A geographic information system is used to facilitate data management and analysis of the results.     

Transportation network reliability in emergency response

Distribution of humanitarian supplies is vital in saving lives during disasters. Investment in retrofitting critical transportation links reduces casualties as intact links improve flow of relief supplies. In finding critical links, link importance values are derived using the concept of network reliability. A network improvement problem is then solved to minimize death toll. To increase practicality, a heuristic algorithm is proposed to solve real size problems. Results show that initial incremental investments in network improvement are more profound in reducing the death toll than higher budget increments. Moreover, higher relief inventories reduce the death toll when the network is reliable.     

Resilience of urban transportation systems. Concept,characteristics, and methods.

Urban transportation systems are susceptible to disturbances, interruptions, and risks from natural and human causes. The concept of resilience has been introduced into urban transportation systems to reduce the consequences of its disruptions. Recently, this concept has attracted considerable interest from researchers from different areas of transportation and mobility. However, several investigations about this issue were carried out under different perspectives, resulting in a more comprehensive concept, which includes adapting and transforming systems for different levels of equilibrium. This article provides a thorough and conceptual review of resilience applied to urban transportation systems focusing on its definitions, characteristics, and quantification methods. Based on this, the evaluation of the level of resilience of mobility subsystems is discussed to provide the basic framework for generating a tool to assess the resilience of the urban transportation system.     

Retail supply chain network design under operational and disruption risks

Designing robust and resilient retail networks under operational and disruption risks can create substantial competitive advantage. In this paper, a deterministic multiple set-covering model is first proposed. Then, it is extended to a possibilistic scenario-based robust model by scenario generation and disruption profiling to design a robust and resilient retail network. The developed models are validated through randomly generated examples and a real case study in retailing. Numerical results demonstrate that designing retail chains without considering operational and disruption risks is really misleading. Also, multiple covering of retail stores as the measure of redundancy increases the network’s resilience significantly.     

A complex network approach towards modeling and analysis of the Australian Airport Network

An airport network forms the backbone of any air transportation system. The relationships among the origins and destinations of flights result in a complex network of routes which can be complemented with information associated with the routes themselves, for instance, traffic load and distance. In this paper, we modeled the Australia's civil domestic airport infrastructure as a network and analyzed the resulting network structure and its features using complex network tool. This case study identifies and investigates complex network measures, such as the degree distribution, characteristics path length, clustering coefficient and centrality measure as well as the correlations among them to understand the topology of an airport network. This analysis of the Australian Airport Network (AAN) indicates that it has a cumulative degree distribution described by the power-law function. As it has an average path length of 2.90, it is considered to have small-world properties. It is also found that it has a clustering coefficient of 0.50 which is higher than that of a random network of the same size which indicates that the transitivity and cohesiveness of AAN is different from a random network. In contrast to the World-wide Airport Network (WAN), the AAN is found to have disassortative mixing similar to the airport networks of China and India.     

Embedding economies of scale concepts for hub network design

We explore the idea of endogenous hub location on a network. In contrast to much of the literature, we propose that hub networks may emerge naturally out of a set of assumptions and conditions borrowed from equilibrium traffic assignment. To this end, we focus on applying a nonlinear cost function that rewards economies of scale on all network links. A model is presented and implemented in a GIS environment using both a 100-node intercity matrix and several synthesized interaction matrices. We compare solutions for different assumptions about network costs, and visualize the results. We find that under discounted conditions, network flow is re-routed to take advantage of the cost savings for amalgamation and that several cities emerge as centers through which large amounts of flow pass. Larger cities such as Los Angeles, New York and Chicago serve gateway functions. We also find that smaller cities such as Oklahoma City, Pittsburgh, Indianapolis, and Knoxville serve major gateway functions because of their locational advantages. Our paper should be of interest to the planner of a surface transportation system, or those interested in nodal concepts such as gateways and transport geography. Results are discussed in light of hub and spoke networks and suggestions are made for future research.     

Hub network design problems with profits

This paper presents a class of hub network design problems with profit-oriented objectives, which extend several families of classical hub location problems. Potential applications arise in the design of air and ground transportation networks. These problems include decisions on the origin/destination nodes that will be served as well as the activation of different types of edges, and consider the simultaneous optimization of the collected profit, setup cost of the hub network and transportation cost. Alternative models and integer programming formulations are proposed and analyzed. Results from computational experiments show the complexity of such models and highlight their superiority for decision-making.     

南通市综合交通枢纽布局优化对策

为推进南通市交通运输转型发展,优化交通基础设施空间一体布局,在经济增长中发挥好支撑引领作用,在阐述南通市综合交通枢纽布局现状、发展定位和存在问题的基础上,从强化对外综合运输通道建设、畅通周边城市城际交通网络、提升市域集散网覆盖通达水平、大力发展多式联运系统和促进综合货运枢纽高效衔接5个方面提出南通市综合交通枢纽布局优化对策。综合交通枢纽的布局优化,有利于完善南通市的枢纽功能,进一步提升其在全国综合交通体系中的战略地位,发展枢纽经济,实现经济转型,加快打造成长三角北冀经济中心。     

青藏线运输能力适应性综合评价分析

在分析影响青藏线运输能力因素的基础上,建立了青藏线运输能力适应性模糊综合评价指标体系和模型,分3个层次对该线运输能力适应性进行综合评价,认为青藏线运输能力适应性水平是高的,整个运输组织方案是可行的,但还需对特大灾害和事故下的应对方案和措施进行研究。     

The structures and flows of a large tourist itinerancy network

This paper undertakes a detailed network analysis (NA) of the structures and flows of a large tourist itinerancy network emerging in six Southeast Asian countries, developed by aggregating 1668 tour itineraries accessed from 149 tour marketing websites. The analysis includes the examination of the network and of seven extracted subnetworks (modules). It identifies various macro-patterns in the network influenced by scale freeness, preferential attachment, and growth. It proposes that a small number of nodes and edges form supercores. These dynamical elements influence the network's emergence, which is occurring without central coordination. A network backbone formed by these supercores emphasizes the flows in the network. The implications are visualized by several conceptual models of tourist and related resource and revenue flows. It identifies that a basin and sink topology, which drains flows from the periphery towards a network backbone sink, is consistent with preferential attachment processes in the network. This paper assists in turning NA in tourism from textile metaphors towards research centred upon empirical relational data. In this case, it exposes a network emerging from the inherent physical connectedness of tourism.     

Air express network design based on express path choices – Chinese case study

Due to the shortage of cargo aircraft, Chinese express companies have to provide transportation services with a hybrid method that consists of “rented bellies and self-owned cargo aircraft”. Because the bellies are rented from air passenger companies and because the cargo aircraft are owned by the express companies, it is important for the express companies to use their cargo aircraft as effectively as possible. This paper constructs a bi-level model to optimize the flight transportation network of an express company. The upper model designs the network and allocates the transportation capacity with the objective of minimizing the total transportation cost, and the lower model calculates the link flows in user equilibrium. Data from ShunFeng (SF) Express Company (China) are used to conduct the case study. Using the model outputs, the flows on links and at nodes are analyzed to illustrate the transportation and transshipment situations.     

Connecting African urban areas: airline networks and intra-Sub-Saharan trade

Despite efforts to enhance the efficiency of the African air transportation sector through such actions the Yamoussoukro Decision, African represents less than 2% of the world’s air passenger kilometers. This is despite the fact that air transportation can act as a means of transporting traded goods directly (including the individuals that are the “product” of tourism) and provide complementary services of labor mobility for those engaged in the production of more bulky goods that are shipped by land and maritime modes. We examine the network of intra-Sub-Saharan African airline connections to highlight the differential access enjoyed by the region’s largest cities. Second, we develop a quantitative framework linking the availability of air connections to the main international trade flows in sub-Sahara Africa. Our findings suggest that, although there is a positive link between air transportation and economic development in Africa, the multilateral efforts at reducing institutional impediments to more open aviation markets have not produced significant results.     

Fair profit contract for a carrier collaboration framework in a green hub network under soft time-windows: Dual lexicographic max–min approach

This paper models a novel and practical bi-objective hub-location problem under a centralized carrier collaboration framework between one holding company and multiple carriers. The holding company first establishes a hub-and-spoke network in order to locate p hubs and to assign the center nodes to the located hubs. Then, it allocates the transportation routes of the hub network to the carriers. In contrast, the carriers should select an appropriate vehicle type to serve the transportation requests in a green hub network. The carriers are also able to meet the transportation requests within a certain time-window based on a soft time-window mechanism. Moreover, aiming to emphasize green transportation, a vehicle emission model is used to take into account CO₂ emissions of the vehicles where the fuel consumption is a function of speed level. Aiming to identify a win–win deal between the holding company and the carriers, a dual lexicographic max–min (LMM) approach is used in order to optimize their profits in a fair way. Finally, some numerical experiments are presented to demonstrate the applicability of the proposed methodology. The computational results show that not only the holding company and the carriers can better generate a fair profit contract among themselves using the LMM approach, but also both can obtain more profit in the worst case for their businesses rather than using the max–min approach. In addition, sensitivity analyses show that increasing the size of the soft time-window leads to a reduction in the delivery schedule violations, while results in raising the total profit. Moreover, the tax cost of fuel consumption as well as the number of potential vehicles has a substantial impact on both the fuel consumption and carrier’s profit.     

Connectivity of the European airport network: “Self-help hubbing” and business implications

This paper investigates the connectivity of the European air transportation network. A time-dependent minimum path approach is employed to calculate the minimum travel time between each pair of airports in the network, inclusive of flight times and waiting times. The connectivity offered by each alliance's network is compared with that of the overall network. The results show that roughly two-thirds of the fastest indirect connections are not operated by the alliance system; this could be exploited to enable a new passenger strategy of “self-help hubbing”.