This paper deals with transit quality-of-service and focuses on reliability. Starting from AVL data collected in a case study, advantages and limitations of the TCQSM method for LOS estimation are discussed. In particular this method is clear, simple and easy to use, but sometimes it may lead to inconsistent LOS estimations because:
• it does not consider the amount of delay but only the number of trips which are late;
• it does not address adequately the effect of early departures on users;
• it introduces a fixed tolerance (3 minutes in advance and 5 minutes late) around the schedule to consider “on-time” a trip.
A new service measure called “weighted delay index” is proposed which allows to overcome these limitations. In this paper a methodology for its estimation is presented and new reliability LOS ranges and thresholds are proposed.
Both TCQSM method and the proposed one have been applied to four routes belonging to Trieste transit network in Italy. The basic data have been collected through the AVL system during the peak hours of a month. The results have been compared with reference to real data and it seems that the proposed approach could lead to more graduated LOS estimation due to the higher number of parameters introduced in the new transit service measure.
