Various warning systems are being studied in the world to improve traffic safety. To enhance the information/warning systems, systems that are based on sensors installed on the roadside are under research. The system informs the driver of the traffic condition through the in-vehicle display and/or the roadside message board. We have evaluated effectiveness and risk of the forward obstacles collision avoidance support system using the driving simulator (DS) in Japan Automobile Research Institute (JARI). As a new evaluation criteria of the effectiveness the velocity at 100m ahead the obstacle was introduced that is able to show the difference of effectiveness of each type of information more clearly. The evaluation results shows that the forward obstacles collision avoidance support system is effective, especially when using the combination of the in -vehicle and the roadside massage information. Next, as a new evaluation method for system risk the driver-system integrated erroneous operation probability model was introduced. The result shows that the accident reduction ratio is 86%.