2023

Tiusanen, Risto; Heikkilä, Eetu; Välisalo, Tero; Malm, Timo

Development towards higher grade of automation (GoA) levels has been a global trend in trains and metros, but so far not in trams due to their complex and highly dynamic operating environment. However, currently rail operators are also showing increasing interest on higher automation levels in tram systems to increase their efficiency and safety. Higher GoA levels in a tram system introduces changes in operating principles, new roles for personnel, and new types of safety risks in daily operations. In this report, we present two studies where risk analysis methods were applied in the conceptual level to identify new autonomy related safety risks in tram operations. The goal of this study was to identify and analyse the effects of increasing level of tram autonomy (from GoA1 to GoA4) on the use of automated tram door and its functionalities. The objectives were to identify the different operating situations of the automatic tram door system, analyse the related safety and availability risks, and define the necessary safety measures.<br/>The results of the PHA and STPA analyses show that parts of the door systems are already capable for GoA4 tram operations. There are safety systems ensuring that the doors do not open when the tram is in motion, and to detect obstacles between the doors. Solutions to ensure accessibility and safe entry and exit for all passengers must be developed for GoA4 operation considering especially passengers who move slowly, have reduced mobility, use wheelchair or are visually impaired. Managing of abnormal situations and emergencies needs to be carefully considered in GoA4 operation. For example, to ensure that the tram can be evacuated safely if needed, and that management of technical and human disturbances with the door systems could be managed remotely.<br/>The door system, however, is only one aspect of the tram operation and other parts are subject to significant changes. Thus, on the path towards automated tram operations, comprehensive safety analyses of all parts of the system and operations are still needed. Systemic methods, such as STPA, can be applied to support these analyses. The results of the analyses can be used to support development of the door systems by focusing the development actions into the areas where the major changes and improvement needs are expected.