Road safety has become a major concern and many strategies have been introduced to reduce road risk and mitigate severe consequences of unavoidable crashes. This paper presents an innovative methodology which aims at monitoring in real time and even anticipating crash risk on Swiss motorways based on detectors providing individual traffic data. Two safety indicators are studied: from their sensitivity to their results on real-world rear-end crashes. Platoon Braking Time Risk is found to be better than the classic Time-To-Collision indicator.