def before_reset(self) -> None:
        """
        Clear the scene and then reset the scene to empty
        :return: None
        """
        super(PGTrafficManager, self).before_reset()
        self.density = self.engine.global_config["traffic_density"]
        self.block_triggered_vehicles = []
        self._traffic_vehicles = []

        Clear the scene and then reset the scene to empty
        :return: None
        
metadrive/manager/traffic_manager.py