# Improving the Functional Reliability of an Urban Public Transport Line
## 3 Results and Discussion
### Random Disruptions in Planned Trans' Circulation  
Events of the nature of risks or uncertainties that affect the operation of the components of the public urban transportation system may also negatively affect the functional reliability of the announced service. The interruption of the electricity supply, in the case of a tram line, for example, paralyzes the movement of all trans in both directions of traffic (except in the rare case where they would be equipped with batteries or supercapacitors). Other specific malfunctions of the running track (rail break or track blocking) or of a tram unable to run are likely to block traffic, initially locally. So that then, depending on the duration, the blockage spreads over shorter or longer distances with potential traffic disruptions on the entire line. Especially when the effects produced cannot be counteracted by the parking reserves of the trans at the ends of the line. In fact, in the case of unidirectional trans, this is the only possibility to mitigate or compensate for deviations from the schedule in the case of disruptive events. In the case of bi-directional trans together with the crossover links between the tracks corresponding to the two directions of traffic (the diagonal in \(\text{m}_{1}\), for example), the effects of the functionality degradation of the scheduled service can be significantly diminished. Figures 9 and 10 illustrate the evaluation frame of negative effects on the planned schedule if, in the same area of the line \(Z_{l}\) a disruptive event occurs that interrupts circulation (for the same duration \(\Delta\)) in the direction from \(Z_{l}\) to B. Figure 9 corresponds to the breakdown of a tram that can no longer run and for which it is required a duration \(\Delta\) of the intervention for restarting circulation. Figure 9: Disturbed circulation by the failure of a tram for a duration \(\Delta\), in the direction from A to B in the zone \(Z_{l}\). Similarly, Figure 10 corresponds to a rail failure or an obstacle in the track area that blocks the movement in the direction from \(Z_{l}\) to B. Both figures present solutions for the adaptation of tram circulation in the situation of that random event. The rescheduling solutions are specific. Just as the effects of planned circulation disruption are specific. It is easy to notice that the negative effects are larger when the tram breaks down (a more likely situation) than those caused by the loss of track functionality. However, not only does the nature and duration of the disruptive event bring particularity in the size of the disturbances produced in the scheduled circulation, but also the moment and the position related to the two end-stops of the line when the event occurs on the line yield particularity. Of course, the positioning in relation to the \(m_{1}\) zone is a matter of record. That is why Figure 11 (in which the area where it was possible to pass from one path to another was eliminated) highlights the different effects of the disruptive event in zone \(Z_{l}\), respectively, zone \(Z_{k}\). The solutions to reduce the disruptive effects of random negative events can include the extreme solution of stopping both traffic directions in a certain area. Moreover, the picture is not complete. Concerning this diversity of disruptive events with specific negative consequences and with specific solutions to limit deviations from the scheduled circulation, we appreciate that references to the functional reliability of the service during the disruptive event and after its clearance and the resuming of the scheduled circulation remain the responsibility of the TPO. It is the one who must promptly inform the users about the best estimation of the disruption, the maximum headway of terms during the event, and the estimated moment for the return to planned scheduled circulation, depending on each specific situation and using the most appropriate means. However, our current analysis has limitations.