This paper presents a high level Petri net modeling methodology for railway systems safety critical scenarios. This methodology is based on modular high level Petri nets, including most relevant components of a railway safety system, as safety regulation procedures, interlocking and especially human factors, enabling more various gathering of information and allowing the study of diverse possibilities in a same global model. At first, this method was applied to the infrastructure and the regulation of the Moroccan Kenitra railway station. Afterward, a first approach of real accident scenario modeling was introduced for 'Saint Romain en Gier' accident, taking account of human errors. Our goal is to bring formal tools in order to study weaknesses in shunting management within train stations and accidental scenarios, considering automatic mechanisms and human involvement.