1. Field of Invention
The invention relates to a traffic information retrieval method and a traffic information retrieval system.
2. Description of Related Art
Conventionally, many vehicle navigation apparatuses have been used in order to support smooth-driving of a vehicle. This smooth-driving is achieved by superimposing a present position of the traveling vehicle and a route from a present position to a destination using road maps displayed on a display. A communication function carried out in such a conventional vehicle navigation apparatus permits real-time display of traffic information, for example traffic congestion and traffic accidents, as well as permits display of a present position of the vehicle and a route. At present, such function and a system thereof are actualized in a VICS (Vehicle Information and Communication System).
In the VICS, the traffic information, like traffic congestion and traffic accidents, are received in the vehicle navigation apparatus. When the traffic information is received, the navigation apparatus starts to change the colors used to represent roads or intersections, from which the traffic information is given, on a road map. Further, navigational arrows are additionally displayed near the color-changed roads or intersections. The user can check the spot where the traffic congestion is increased or the scene of the traffic accident. Such check helps the user to select the optimal road to circumvent the traffic congestion spot or the scene of the traffic accident.
The user does not always need the traffic information about the present position of the vehicle. The user sometimes needs traffic information, for example, which identifies the traffic congestion or the traffic accident which happens beyond a range of the currently displayed road map. In such a case, the user manually operates a key-switch in the vehicle navigation apparatus in order to display the road on which the user wants to know the traffic information. By this manual operation, the map of the road on which the user wants to know the traffic information is displayed. This is how the user can check the traffic information about the road displayed on the map.
Further, the traffic information changes moment by moment. In detail, there is a possibility that traffic congestion is relieved while the vehicle is traveling from a present position to the traffic congestion spot or a possibility that a new traffic accident occurs while the vehicle is traveling from a present position to the destination. The user thus does not always need real-time traffic information but rather wants to obtain future traffic information. In VICS, only the real-time information is obtained. Therefore the user may regard sometimes the VICS information only for reference purposes.