Investments in public transport projects are increasingly motivated not merely based on travel time savings but also in relation to improvements in service reliability, comfort and robustness. However, there are no standard practices for incorporating the impacts of alternative investments on network robustness.
Together with Erik Jenelius from KTH, a methodology for assessing the value of new links for public transport network robustness, considering disruptions of other lines and links as well as the new links themselves, was developed. We applied this methodology to a light rail line in Stockholm.
A distinction is made between the value of robustness, defined as the change in welfare during disruption compared to the baseline network, and the value of redundancy, defined as the change in welfare losses due to disruption. Topological studies concluded that redundancy is an important feature for network robustness. Interestingly, we found that In some cases, the new line results with seemingly paradoxical effects as it leads to greater disruption costs.