An assessment of alternative bus reliability indicators

Traditionally, there has been an emphasis amongst transport operators to collect statistics on operational performance such as % Buses Cancelled, % Departing On-time and % Arriving On-time. These 'operational' measures remain popular because the statistics are easy to understand and the data is relatively easy to collect especially if 'self-reported' by drivers. In addition, historical trends have usually been established and, as many operators use them, there is within industry comparability. This paper has reviewed these operationally based statistics with seven other indicators of urban bus service reliability using an assessment framework and an assembly of evidence drawn from a study undertaken for the NSW Independent Transport Safety and Reliability Regulator (ITSRR) in 2006. The original 2006 review concluded that excess waiting time (EWT) was the preferred measure for high frequency bus services with the percentage of buses running on-time the preferred indicator for low frequency services with little to choose between measuring arrival versus departure times. This paper has updated the 2006 review to take account of developments in the automatic collection of travel time data on buses and trains. For rail in Sydney, the incorporation of control systems that record the time of day at which trains are at stations has enabled a new measure of customer journey time delay (CJTD) to be developed that incorporates 'at station' and 'on train' delays and can be calculated for both frequent and infrequent services. When considered alongside the other nine reliability indicators, the new CJTD measure ranked equal top with EWT. Both measures were considered easy to understand and have a high customer focus. Where they differed was in terms of fidelity/objectivity and cost efficiency. EWT is a partial measure since it excludes on-board delay whereas CJTD is a total measure incorporating 'at stop' and 'on bus' delay. EWT is also only appropriate for high frequency services whereas CJTD is applicable to low and high frequency services. In terms of data collection, EWT is more feasible since it only requires information at unlinked bus stops whereas CJTD requires stop to stop bus times which are far more onerous to collect. However with automatic collection of travel times, CJTD should become a practically feasible measure for bus as has already been demonstrated for rail in Sydney.