In this paper, we model the Feared Event (Collision between train and vehicle) of the Moroccan level crossing system using Fault Trees, in order to evaluate the unreliability of the system and to identify the critical components. First, a fault tree analysis to evaluate the system unreliability over the time is proposed. The human factors and components failure rates are taken into account. Then, an importance measures study is proposed to identify the critical components in the level crossing system.