Using complex network theory to describe the relational geography of maritime networks has provided great insights regarding their hierarchy and evolution over the past two decades. Unlike applications in other transport fields, notably air transport, complex network theory has had limited application in studying the vulnerability of maritime networks. This study uses targeted link disruption to investigate the strategy specific vulnerability of the network. Although nodal infrastructure such as ports can render a network vulnerable as a result of labour strikes, trade embargoes or natural disasters, it is the shipping lines connecting the ports that are more probably disrupted, either from within the industry, or outside. In this paper we apply and evaluate two link-based disruption strategies on the global container shipping network, one based on link betweenness, and the other on link salience, to emulate the impact of large-scale service reconfiguration affecting priority links. The results show that the network is by and large robust to such reconfiguration. Meanwhile the flexibility of the network is reduced by both strategies, but to a greater degree by betweenness, resulting in a reduction of transshipment and dynamic rerouting potential amongst the busiest port regions. The results further show that the salience strategy is highly effective in reducing the commonality of shortest path sets, thereby diminishing opportunities for freight consolidation and scale economies.

A country’s competitiveness can be severely hampered by an uncompetitive freight logistics system. During the first decade of the 21st century, two in-depth models were developed for South Africa which provide a framework for measuring and improving the country’s freight logistics system – the cost of logistics survey and the freight demand model. These models also allow for the development of scenarios for key identified risks. The objectives of this study were to provide an overview of South Africa’s surface freight transport industry,identify key risks to national competitiveness and suggest ways in which these risks could be mitigated. Freight flows were modelled by disaggregating the national input–output model into 372 origin–destination pairs and 71 commodity groups, followed by distance decay gravity-modelling. Logistics costs were calculated by relating commodity-level freight flows to the costs of fulfilling associated logistical functions. South Africa’s economy is highly transport intensive. Excessive dependence on road freight transport exacerbates this situation. Furthermore, the road freight transport’s key cost driver is fuel, driven in turn by the oil price. Scenario analysis indicated the risk posed by this rising and volatile input and should provide impetus for policy instruments to reduce transport intensity. As such, this study concluded that a reduction in freight transport intensity is required to reduce exposure to volatile international oil prices.

Making a supply chain more resilient and making it more efficient are often diametrically opposed objectives. Managers have to make informed trade-offs when designing their supply chain networks. There are many methods available to quantify and optimise efficiency. Unfortunately the same cannot be said for vulnerability and resilience. We propose a method to quantify the impact that a supply chain's dependence on the underlying transport infrastructure has on its vulnerability. The dependence relationship is modelled using multilayered complex network theory. We develop two metrics relating to the unique collection of shortest path sets namely redundancy and overlap. To test the relationships between these metrics and supply chain vulnerability we simulate progressive random link disruption of the urban road network and assess the impact this has on Fully Connected, Single Hub and Double Hub network archetypes. The results show that redundancy and overlap of the collection of shortest paths are significantly related to supply chain resilience, however under a purely random disturbance regime they hold no predictive power. This paper builds a foundation for a new field of inquiry into supply chain vulnerability by presenting a flexible mathematical formulation of the multilayered network and defining and testing two novel metrics that could be incorporated into supply chain network design decisions. Keywords supply chain vulnerability • urban road network • multilayer complex network • shortest paths • link betweenness This article has been published and should be cited as: Viljoen, N. M., & Joubert, J. W. (2018). The road most travelled: The impact of urban road infrastructure on supply chain network vulnerability. Networks and Spatial Economics, 18(1), 85-113.

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Background: South Africa has a disproportionately high freight transport demand owing to industrial development far from ports, low domestic beneficiation and improper modal use. Historical freight transport policy supported primary economic development, failing to preempt the changing economic structure and the resulting freight transport needs, resulting in excessive transport costs and externalities.Objectives: To share the macroeconomic freight transport challenges revealed by South Africa’s Logistics Barometer, and to identify key interventions to address these.Method: Freight flows are modelled by disaggregating the national input–output model into 83 commodity groupings and 372 geographical areas, culminating in a 30-year forecast at 5-year intervals for three scenarios, followed by distance-decay gravity modelling to determine freight flows. Logistics costs are calculated by relating these flows to the costs of fulfilling associated logistic functions.Results: Long-distance transport remains the largest general freight typology and is, due to inefficient macro logistics design, extremely costly, both in terms of intrinsic and extrinsic costs.Conclusion: South Africa’s freight task will grow 2.5-fold by 2043. Logistics and externality costs are already untenable at current levels. The development of domestic intermodal solutions will support the drive towards sustainable freight mobility.

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This article presents the multilayered complex network formulation for three different supply chain network archetypes on an urban road grid and describes how 500 instances were randomly generated for each archetype. Both the supply chain network layer and the urban road network layer are directed unweighted networks. The shortest path set is calculated for each of the 1 500 experimental instances. The datasets are used to empirically explore the impact that the supply chain's dependence on the transport network has on its vulnerability in Viljoen and Joubert (2017) [1]. The datasets are publicly available on Mendeley (Joubert and Viljoen, 2017) [2].

Disasters are becoming an unavoidable part of everyday life throughout the world, including South Africa. Even though South Africa is not a country affected by large-scale disasters such as earthquakes, the impact of disasters in South Africa is aggravated significantly by the vulnerability of people living in informal settlements. Humanitarian logistics, as a ‘new’ sub-field in the supply chain management context, has developed significantly recently to assist in disaster situations. This paper provides an overview of the South African humanitarian logistics context. Even though humanitarian logistics plays a critical role in the aftermath of disasters, it extends far beyond events that can typically be classified as ‘disasters’. Therefore the implication of the South African humanitarian logistics context on future research and collaboration opportunities in South African humanitarian logistics is also discussed. Finally, two recent case studies in the South African humanitarian logistics environment are discussed.