Dangerous driving behaviors can lead to traffic accidents. However, there is a lack of systematic real-Time driving monitoring and alerting mechanism. In this paper, nine major dangerous driving behaviors are identified and defined based on past researches and experiences. An on-board safety driving assistance system, which utilizes in-vehicle dynamics and real-Time traffic information, is proposed to instantly detect dangerous driving behaviors and alert the driver during driving periods. The in-vehicle dynamics are collected from On-Board Diagnostics (OBD-II), an accelerometer and a gyroscope. The real-Time traffic information is collected from a camera with image processing. The proposed system is implemented on a CPU board with a user interface (UI), which shows alerting icons when dangerous behaviors occur.