<p>A traffic flow control system in which a mobile information device and control server capable of having a conversation with the user in a vehicle are connected through a communication network. The mobile information device includes a route information setting section for setting route information including a departure place, a destination, a route, and a main place arrival expected time on the basis of the conversation with the user and a route information transmitting section for transmitting the route information to the control server. The control server includes a control policy determining section for computing the predicted traffic amount and delay time of each intersection or each link by using the route information collected from each vehicle and detecting an abnormal delay point to create delay avoidance point information and a signal parameter computing section for varying the value of the parameter of each traffic signal on the basis of the delay avoidance point information.</p>
