Investments in transport are increasingly motivated by the need to improve its robustness — the capacity to absorb disturbances with a minimal impact on system performance. Nonetheless, there is lack of knowledge on how to assess and quantify the robustness value of new investments as part of strategic planning. This study investigates the robustness of alternative public transport networks by assessing the consequences of link failures on network performance. A full-scan disruption impact analysis is performed and its implications on passenger’s group composition and travel time losses are analysed for a public transport development plan in Stockholm, Sweden. A decision to extend this system substantially with 23 new stations and 35 km of new tracks by 2025 was recently undertaken.
The results suggest that as a result of the development plan, the robustness of the case study network will improve in terms of average performance deterioration as well as worst case scenario for all performance indicators. Neglecting abnormal operations in project appraisal can potentially lead to the underestimation of its benefits. Moreover, the critical links in each network are identified and impact disparity is investigated. The analysis method presented in this study can support the consideration of development plan impacts on network robustness in the strategic planning process.