Driver inattentiveness and distraction resulting in unsafe vehicle maneuvers are a significant safety concern because such behavior can directly lead to crashes. An effective technical countermeasure is to detect unsafe driving events and provide drivers with advanced warning information. This study presents an intervehicle safety warning information system. An inertial measurement unit consisting of an accelerometer and gyro sensor in addition to a Global Positioning System receiver was used to collect data for the developed algorithm. Vehicle position, speed, acceleration, and angular velocity data were analyzed and were used as inputs for the algorithm. A support vector machine classifier was also incorporated into the algorithm to identify further the severity of unsafe driving events. The performance evaluation results showed that the detection algorithm could capture longitudinal and transverse unsafe driving events. In addition, a prototype of the proposed warning information system was implemented on a test bed in support of vehicle-to-vehicle and vehicle-to-infrastructure communications. Extensive field tests have been conducted in the test bed to fine-tune the prototypical system. These results demonstrate that the system holds promise for improving drivers' safety and mitigating crash risks.