To limit entering vehicles at a road entrance while informing users of a traffic congestion distance before they enter a freeway, and relieve the traffic congestion by temporarily storing a radio wave from an automobile that a sensor detects, and sending the calculated congestion distance and entrance control data to a display part and an entrance control part.

A radio wave transmission part 1 mounted on each automobile sends a radio wave which has a unique frequency as well as a license plate and constant output. Sensors 2 which are installed on the side wall of the road at constant intervals capture radio waves sent from respective automobiles and the data reception part 4 of a central monitor and control device 3 catches the radio waves from the sensors 2 directly and temporarily stores a storage part 5 with data consisting of sensor ID numbers and the number of the automobiles. Then a central arithmetic part 6 calculates the distance and section of the traffic congestion and further entrances whose entries should be limited to reduce the traffic congestion on the basis of the data, and the calculation data are sent to the display part 8 and entrance control part 9 to display the traffic congestion state to the users and limit the entries.