Measuring public transport accessibility to fixed activities and discretionary opportunities: a space-time approach

The Space-Time Accessibility (STA) model is broadly used to measure person-based accessibility based on the space, time, and transport constraints experienced at the individual level in connection to the actual modal choices of observed individuals. In this paper, we propose to adjust the STA model (by introducing a so-called PT-STA model) with three core purposes: (1) focusing on public transport accessibility specifically, (2) measuring accessibility to both fixed activities and discretionary opportunities, and (3) integrating travel-time thresholds in the accessibility measurement. These three elements aim to make the PT-STA model a suitable tool to evaluate the impacts of public transport interventions on person-based accessibility and extend the evaluation of public transport accessibility to its fixed and discretionary dimensions. The PT-STA model is tested with a sample of 118 residents of the rural municipality of Mühlwald (South Tyrol, Italy). Results show that the accessibility to fixed activities and discretionary opportunities are limitedly correlated. It is possible to identify people with high accessibility to fixed activities and poor access to discretionary opportunities (typically pensioners and homemakers living in remote locations) and vice versa (e.g. people with articulated rural-urban commutes but daily visiting locations with several amenities). These results preliminarily confirm the importance of combining both accessibility dimensions in the PT-STA model since they tell complementary and not overlapped stories that are relevant for policymakers to evaluate the pros and cons of alternative public transport interventions.