Quantifying bus travel time variability and identifying spatial and temporal factors using Burr distribution model

Travel time variability (TTV) is the key indicator used in assessing the service quality of bus transit system. This study explores the most appropriate model to describe the day-to-day TTV of bus section. By investigating a 7-month travel time data for 10 bus routes in Klang Valley, Malaysia, this study demonstrates that Burr distribution is the most promising model in describing bus TTV. Bus TTV is found to be sensitive to both temporal and spatial effect. This means that TTV service varies for weekdays and weekends (temporal). Also, it differs for the five operating environments (spatial) investigated in this study. The Burr regression analysis conducted in the second part of this study further confirmed that bus section length and traffic signal density are the major contributing factors to bus TTV. However, both factors have varying levels of impact under different spatiotemporal effect. For example, in the suburban and residential areas, these factors cause higher TTV on weekends but lesser during weekdays, while a vice versa impact is observed in the Central Business District. This distinguishes from earlier studies which purely assumed normality in the regression analysis while not emphasizing the importance of spatiotemporal factors on TTV. Thus, this study serves as an analysis tool that could be used in the planning of bus routes and schedules under varying bus operating environments and operation times.