This paper describes the development and verification of control algorithms for V2X and environmental sensor integrated intersection support and safety systems. The objective of the research is to develop core technologies for effective fusion of V2X and environmental sensors and to develop new safety function for intersection safety. One of core technologies is to achieve the improvement of GPS accuracy, and the other is to develop the algorithm of a vehicle identification which matches all data from V2X, vehicle sensors and environmental sensors to specific vehicles. A intersection optimal pass (IOP) algorithm is designed based on these core technologies. IOP recommends appropriate speed to pass the intersection in the consideration of traffic light signal and preceeding vehicle existence. Another function is developed to prevent a collision avoidance when car crash caused by traffic violation of surrounding vehicles is expected. Finally all functions are implemented and tested in three test vehicles. It is shown that IOP can support convenient and comfortable driving with recommending optimal pass speed and collision avoidance algorithm can effectively prevent collision caused by traffic sign violation of surrounding vehicles.