Public transport experienced service reliability: Integrating travel time and travel conditions

Abstract

The paper proposes a generalization of public transport service reliability, incorporating both travel times and travel conditions based on passengers’ perceived journey time. Time is partitioned into waiting and transfer time as well as in-vehicle time under different travel conditions (crowding and seat availability), which may vary along a journey and between days. The experienced service reliability gap (ESRG) index is introduced, defined as the difference between an upper percentile (e.g., the 95th) and the median perceived journey time across days for a particular OD pair and departure time. The metric is evaluated by tracing virtual trips from origin to destination with journey times and travel conditions based on automated vehicle location (AVL) and automated passenger count (APC) data and seated status modelled probabilistically. A study of a high-frequency bus line in Stockholm, Sweden shows that travel conditions co-vary only weakly with nominal journey time, and the ESRG index display patterns across the day not evident in existing reliability measures, such as a wider and later afternoon peak. The ESRG displays significant variation between OD pairs along the line. Correlation with headway variability suggests that measures improving bus regularity have additional positive effects on experienced service reliability.