Abstract: A driving assisting system includes a traffic signal controller, an RSU, at least one data transmission interface and an OBU. The RSU is electrically connected to the traffic signal controller. The OBU is installed on a vehicle. The traffic signal controller controls a traffic light, which is located at an intersection. The RSU obtains traffic-light information of the traffic light from the traffic signal controller. The OBU receives the traffic-light information through the at least one data transmission interface from the RSU. The OBU generates dynamic vehicle information of the vehicle. The OBU determines if the vehicle will be positioned at a key zone of the intersection when the traffic light switches according to the dynamic vehicle information and the traffic-light information. The OBU responds according to a key zone type of the key zone when the vehicle is positioned at the key zone of the intersection.