Operation automation level in an underground line and service reliability

On the basis of operational observations, carried out on a metro line, equipped with ATP, the achievement is to develop a theoretical formulation of the reliability concept through definition of suitable indices, focussing its aleatory components. It is proved, more over, through data coming from a case study, how automation in line operation reduce variability of such aleatory components, increasing reliability. Headway reliability is one of the most important factors for evaluation of the quality of an underground railway operation. Control and regulation actions have the scope to restore a regular headway of train transit when they shift from the theoretical sequence due to a perturbation. For this reason reliability has been chosen as parameter to evaluate the effects of automation introduction in some operational aspects. It has been defined a reliability index which is the difference between real headway and theoretical headway, measured in a given section of the line. Furthermore a reliability coefficient represent a percentage of reliability index average. Actual headway is a aleatory quantity depending on other aleatory quantities like running times, stop times and times for the headline operations. The concept of the adopted theoretical model is that headway between two train running a certain section is a sum of terms depending upon running time of the section itself, transit time through stations and headline operation time.