Planning for the unplanned – where shall we allocate reserve capacity?

In the field of network vulnerability and resilience, there is growing evident that network redundancy is a key determinant of network capability to withstand shocks. However, introducing redundancy to rapid public transport networks is very expensive and it is thus important to identify the network elements that will benefit most network performance in case of disruption.

It is crucial to invest in network redundancy without making redundant investments!

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Together with my colleague from KTH, Erik Jenelius, we propose and demonstrate in a new paper a methodology for evaluating the effectiveness of a strategic increase in capacity on alternative public transport network links to mitigate the impact of unexpected network disruptions. For a given disruption scenario, a set of links is first identified as candidates for capacity enhancement based on (i) their initial saturation levels in terms of volume to capacity ratios, and (ii) the overloading in terms of increased saturation that occurs due to the disruption. Second, the effect of capacity increase is evaluated for each candidate link by comparing the disruption impacts with and without increased capacity. Based on the evaluation the most effective of the mitigation actions can be identified.

We applied the methodology to  a case study of the high frequency public transport network of Stockholm. To evaluate the public transport system performance under varying conditions, BusMezzo, a dynamic public transport operations and assignment model was used.

The method presented in this paper could support policy makers and operators in prioritizing measures to increase network robustness by improving system capacity to absorb unplanned disruptions.


Click here for the full paper.