# Improving the Functional Reliability of an Urban Public Transport Line
## 4 Conclusions  
1. Increasing the attractiveness of urban public transportation as a solution for limiting the negative effects of individual motorized mobility in the urban environment requires an increasingly better quality of the offer presented to users. The compliance norms for all trained resources, which are in an upward dynamic due to technological progress, are defined for both the technical performances and those of convenience, comfort, safety, and security of the urban public transportation system. However, the transformation of these potential performances into the actual ones, i.e., those revealed to the users, depends on the operating technology adopted by the network manager and the chosen solution for adapting the offer to the estimated demand. From here, it derives the attributes of the service that can be found in the quality of presentation made publicly. 2. According to a fundamental principle of good practice, the public service provider must ensure that the offer presented to potential users never exceeds the performance of the service that can be provided with certainty. The imperative of this principle requires that the manager of each public transport line make a careful analysis. In which, inevitably, they face multiple uncertainties. The spatial and temporal inconsistencies of the task to be performed are only partially possible to be estimated at the time of the service design, as well as the other multitude of unpredictable exogenous or endogenous events that can negatively affect the planned performance of the service. In the end, regardless of the thoroughness of the analysis, the conclusion is the same: full certainty cannot be obtained. Confronted with this reality, the TPO is obliged to present to its users not a certain value of the quality of the service but a range (in this range, the relevant indicators of the quality of the planned service provided will be set with the highest possible probability). Defining service performance in this probabilistic manner refers to the functional reliability. By addressing a range of indicators of good functioning, it means that service functional reliability is a different concept than the reliability of a product or a traffic network (which also has other peculiarities). Analogies are not helpful. Figure 11: Deviations from the scheduled circulation caused by an event that blocks it in the zone \(Z_{k}\) or the zone \(Z_{l}\), in the direction from A to B, for the duration \(\Delta\) (\(T\), \(T_{k}\), \(T_{l}\)—the programmed operating cycles, respectively in case of blocking in the zone \(Z_{k}\), or zone \(Z_{l}\)). Therefore, the functional reliability of public transportation is typically related to the operation of a system. An urban public transport line that brings together infrastructures, means of transport, human operators, and technologies adapted to the planned tasks meets the requirements of a system. Functional reliability is defined by the probability with which the success of the mission is ensured; that means that is systemic reliability. The mission of the service derives from the quality that the users of the service appreciate when they choose public transportation as an alternative to satisfy the need for mobility in urban space. The functional reliability of urban public transport is of the nature of a commitment of the service provider, which also includes the presentation quality and aims to reduce the user's uncertainty related to the performance variability. 4. For the planning of trips, especially the frequent and mandatory ones, functional reliability is distinguished by the importance given by the users (to respect the planned schedule assumed by the operator for each characteristic time). The planned schedule, to a good extent, also reflects the comfort conditions of the trip. The presented analyses on the functional reliability of a tram line consider compliance with the planned schedule for frequent flows, specific to a period of the day, as well as for other operation scenarios.