Assessment of large-scale transitions in public transport networks using open timetable data: case of Helsinki metro extension

Transforming a direct radial network to a trunk-feeder system is an often-argued method of large-scale overhaul in public transport networks. In planning such large-scale network overhauls, planners are often facing a dilemma when trying to achieve a careful balance between efficiency and equity, as overhaul might result in an unequal distribution of benefits and burdens for end users. Despite theoretically well-known trade-offs between trunk-branch and trunk-feeder networks, there are limited empirical studies documented from the user perspective, accounting for both travel time and transfers. Conventional methods used in practice, such as cost-benefit analyses, are often lacking the capacity to take into account equity effects. Having in mind the need for drawing lessons from actual overhauls, this research presents the assessment of changes in travel time and number of transfers brought about by the Helsinki metro extension, which involved the transformation of a direct bus network to a metro system with feeder buses. To this end, we develop a methodology for assessment of large-scale public transport network overhauls, building upon the previous development in service-equity assessment methods. Based on the use of open timetable data, the methodology centers on continuous journey calculations between all public transport access points. Thus, this methodology highlights the changes in travel time and transfers that would not be noticed in an aggregate assessment approach. In particular, the methodology reveals the disaggregate effects of the network overhaul from a three-level spatial perspective. As a result, this before-after study contributes to the understanding of the trade-offs between trunk-branch and trunk-feeder networks, while providing planning process recommendations for future large-scale public transport network overhauls.