Improving the reliability of bus service could increase attractiveness of bus transit to current and prospective passengers. understanding of service reliability is important for developing strategies that could help transit agencies provide better services. This paper presents an analysis of service reliability based on bus operational characteristics in Isfahan using automatic vehicle location (AVL) data. Performance parameters likes, coefficient of variation of travel time ( ), buffer index (BI), variability index (VI), second-order stochastic dominance index (SSDI), planning time index (PTI) and excess equivalent waiting time are proposed for the evaluation of bus service reliability. Using AVL data, service reliability of 15 lines in Isfahan estimated. The results indicate lines with low service reliability. Some lines like 63, 1, 9, 16 and 79 has the lowest amount of travel time reliability amongst the others. BRT line has high service reliability in travel time but it could not perform properly in peak hours. Also, in order to understand the functional differences in different seasons, travel time of the line 34 was measured in two months. We observed a shorter travel time in the December and a greater amount of travel time deviation than April. Also, the peak-hour of December occurs two hours earlier than April. Our headway regularity indicator (SSDI) shows that some of most important lines in Isfahan like 34, 91, 1 and BRT cannot keep their distant from other buses regular until the end of line, and this could lead to bus bunching and increasing passengers waiting time. Recovery time in different lines was also investigated. On the lines 34, 1, and 26, recovery time in terminals is noticeably different to each other, which can reduce reliability. Also, the average speed of the buses in different lines was measured. lines 29, BRT and 5 having highest speeds, and lines 1 and 43 having the lowest speed among the others. in order to improve the bus performance, a headway-base holding strategy was selected. By applying this strategy at Azadi Station, headway regularity (SSDI) decrease from 0.34 to 0.26
