Threshold Enabled Measure to Evaluate the Travel Time Reliability Performance

The tolerance levels at both ends of a bus trip influence the perceived bus transport travel time reliability performance. Existing studies mainly consider the tolerance level at one end only. The objective of this study is to develop a method to evaluate the bus transport travel time reliability performance by defining tolerance levels at both ends of a trip. Threshold Enabled Departure Passenger Waiting Time (TEDPWT) is perceived as the half of Scheduled Departure Headway (SDH) at bus stops for frequent bus services that have uniform Scheduled Departure Headways. Threshold Waiting Time Enabled Departure Headway (TDH) is calculated as the difference between Actual Departure Headway and TEDPWT. By comparing TDH with TEDPWT, departure activity is categorized as Early Departure, Ontime Departure, and Late Departure. Similarly, Threshold Waiting Time Enabled Arrival Headway (TAH) is also defined, and arrival activity is categorized as Early Arrival, Ontime Arrival, and Late Arrival. Crosstabulation is conducted across departure activity levels versus arrival activity levels with respect to type of day (weekday and weekends) and time of the day. This crosstabulation analysis results in statistically significant percentage/probability value for the cross occurrence of the departure activity levels versus arrival activity levels. This percentage /probability value is used as the indicator to evaluate the travel time reliability performance. When applied to suburban feeder-bus routes, a major finding among many was, buses arrived at their destination late though they departed early on weekdays during peak hours. This study contributes to the domain of performance evaluation of bus transport travel time reliability.