Speed limit recognition method and speed limit recognition device

1 . A speed limit recognition method causing a controller to execute processing comprising:

acquiring a captured image representing an environment in front of an own vehicle from a camera;

recognizing a speed limit sign from the captured image acquired by the camera;

determining whether or not a plurality of speed limit signs are recognized from the captured image acquired by the camera;

when determining that only a single speed limit sign is recognized, recognizing a speed limit that the recognized single speed limit sign indicates as a speed limit of a road on which the own vehicle travels;

when determining that the plurality of speed limit signs are recognized, determining whether or not the plurality of speed limit signs include speed limit signs respectively existing in right front and left front of the own vehicle and indicating a same speed limit;

when determining that the plurality of speed limit signs include speed limit signs respectively existing in a right front and a left front of the own vehicle and indicating a same speed limit, recognizing a speed limit indicated by the speed limit signs respectively existing in the right front and the left front of the own vehicle to be a speed limit of a road on which the own vehicle travels;

when determining that the plurality of speed limit signs do not include speed limit signs respectively existing in the right front and the left front of the own vehicle and indicating a same speed limit, determining whether or not the plurality of speed limit signs include a group of speed limit signs close to one another;

when determining that the plurality of speed limit signs include a group of speed limit signs close to one another, recognizing a highest speed among speeds respectively indicated by the group of speed limit signs to be a speed limit of a road on which the own vehicle travels,

when determining that the plurality of speed limit signs do not include a group of speed limit signs close to one another, recognizing a speed limit that a closest speed limit sign to the own vehicle among the plurality of speed limit signs existing in a predetermined direction indicates to be a speed limit of a road on which the own vehicle travels, the predetermined direction being a direction predetermined in advance and fixed as one of a right front direction and a left front direction of the own vehicle; and

automatically setting a vehicle speed of the own vehicle as the recognized speed limit of the road on which the own vehicle travels,

wherein the own vehicle is a vehicle other than a specific type of vehicle to which a relatively low speed limit is applied among a plurality of types of vehicles having different speed limits.

2 . The speed limit recognition method according to claim 1 causing the controller to execute processing comprising:

selecting one speed limit sign of the plurality of speed limit signs;

determining whether or not another speed limit sign of the plurality of speed limit signs exists within a range of a predetermined distance from the one speed limit sign;

when determining that the another speed limit sign exists within a range of a predetermined distance from the one speed limit sign, extracting the one speed limit sign and the another speed limit sign as speed limit signs included in the group of speed limit signs close to one another.

3 . The speed limit recognition method according to claim 1 , causing the controller to execute processing of determining whether or not the plurality of speed limit signs include speed limit signs indicating a same speed limit, one of the speed limit signs existing in the right front of the own vehicle and at a right road edge of the road on which the own vehicle travels, another of the speed limit signs existing in the left front of the own vehicle and at a left road edge of the road on which the own vehicle travels.

4 . A speed limit recognition device comprising:

a camera configured to capture an environment in front of an own vehicle; and

a controller configured to execute processing including recognizing a speed limit sign from a captured image acquired by the camera, determining whether or not a plurality of speed limit signs are recognized from the captured image acquired by the camera, when determining that only a single speed limit sign is recognized, recognizing a speed limit that the recognized single speed limit sign indicates as a speed limit of a road on which the own vehicle travels, when determining that the plurality of speed limit signs are recognized, determining whether or not the plurality of speed limit signs include speed limit signs respectively existing in right front and left front of the own vehicle and indicating a same speed limit, when determining that the plurality of speed limit signs include speed limit signs respectively existing in a right front and a left front of the own vehicle and indicating a same speed limit, recognizing a speed limit indicated by the speed limit signs respectively existing in the right front and the left front of the own vehicle to be a speed limit of a road on which the own vehicle travels, when determining that the plurality of speed limit signs do not include speed limit signs respectively existing in the right front and the left front of the own vehicle and indicating a same speed limit, determining whether or not the plurality of speed limit signs include a group of speed limit signs close to one another, and when determining that the plurality of speed limit signs include a group of speed limit signs close to one another, recognizing a highest speed among speeds respectively indicated by the group of speed limit signs to be a speed limit of a road on which the own vehicle travels, when determining that the plurality of speed limit signs do not include a group of speed limit signs close to one another, recognizing a speed limit that a closest speed limit sign to the own vehicle among the plurality of speed limit signs existing in a predetermined direction indicates to be a speed limit of a road on which the own vehicle travels, the predetermined direction being a direction predetermined in advance and fixed as one of a right front direction and a left front direction of the own vehicle, and automatically setting a vehicle speed of the own vehicle as the recognized speed limit of the road on which the own vehicle travels, wherein the own vehicle is a vehicle other than a specific type of vehicle to which a relatively low speed limit is applied among a plurality of types of vehicles having different speed limits.

5 . The speed limit recognition device according to claim 4 , wherein the controller executes processing of determining whether or not the plurality of speed limit signs include speed limit signs indicating a same speed limit, one of the speed limit signs existing in the right front of the own vehicle and at a right road edge of the road on which the own vehicle travels, another of the speed limit signs existing in the left front of the own vehicle and at a left road edge of the road on which the own vehicle travels.