Model of Safety Layers in the Railway System - MoSiS

The Institute of Transportation Systems of the DLR is engaged with research regarding operational safety and human factors in railways. The aim is to develop a model of safety layers in the railway system (MoSiS) to make safety scaleable. This paper presents the basic approach to achieve this aim. With a model of safety layers it will be possible to look at the safety of a railway system in a modular way. That means it will be possible to establish a cost-effective safety concept, appropriate for the particular application area, and also to prove that the safety is appropriate. The identification of safety layers is done by systematic analysis of accidents and near accidents using Why Because Analysis (WBA). The first methodical analysis to develop a safety layer model is done using a level crossing as an example. WBA is used to identify gaps in the existing safety layers of the railway crossing. Subsequently the gaps can be categorised. To illustrate the layers and their existing gaps the Swiss Cheese Theory has been chosen. In parallel the current status of safety layers is described. The layers identified this way will contribute to the development of MoSiS. In addition to existing layers new layers can be developed and then be added to MoSiS. A comprehensive portfolio of safety layers will be available. It will then be possible to close gaps systematically. Alternative safety concepts – here for a railway crossing as an example – are expected as a result. Further analysis is planned regarding the following questions: Can layers be exchanged? Is it possible to abandon some layers completely without reducing safety? How do new layers that enhance the ratio between safety and economy have to look like? The final result shall be that a portfolio of existing safety layers in the railway system is known and described. The knowledge of the structure and the state of these layers gives the possibility to describe the number and the “position” of gaps. This way one can design cost-effective solutions to fill these gaps. New developed operational or technical safety concepts can even be validated using MoSiS