Computing the Buffer Times to Absorb The Disruptions In An Urban Railway System by Fuzzy Approach, Including a Case Study

The aim of this paper is to manage the train disruptions in block sections as well as stations to reach the desired reliability. It is necessary to note that in the case that the disruptions are not absorbed, the delays propagate from one train to the next one. Therefore, absorbing the disruptions is an important issue. In the classical method to define the buffer times in operation plan studies is to consider 5 seconds for each kilometer. In this paper, it is aimed to compute the exact amountof buffer times and locate them in convenient parts of timetables. To that end, a new mathematical model based on fuzzy approach is proposed to compute the buffer times. Moreover, the lower and upper bounds of fuzzy limits are determined by some new methods as well as a heuristic algorithm. Finally, to illustrate the applicability, and analyze the performance of the proposed method, some random examples as well as an Iranian case study are analyzed and the results are reported. The final results shows that by this new method the required buffer times are defined more precisely and consequently the computation of required number of trains as well as the number of parking lines can be done more accurate and reliable.