def get_negative_lanes(self):
        """
        In order to remain the lane index, ret is a 2-dim array structure like like [Road_lanes[lane_1, lane_2]]
        """
        ret = []
        for _from, _to_dict in self.graph.items():
            for _to, lanes in _to_dict.items():
                road = Road(_from, _to)
                if road.is_negative_road() and road.is_valid_road():
                    ret.append(lanes)
        return ret

        In order to remain the lane index, ret is a 2-dim array structure like like [Road_lanes[lane_1, lane_2]]
        
metadrive/component/road_network/node_road_network.py