def allow_respawn(self):
        """In native implementation, we can only respawn new vehicle when the total vehicles in the scene
        is less then num_agents. But here, since we always have N-K IDM vehicles and K RL vehicles, so
        allow_respawn is always False. We set to True to allow spawning new vehicle.
        """
        if self._allow_respawn is False:
            return False

        if len(self.active_agents) < self.engine.global_config["num_agents"]:
            return True

        if len(self.RL_agents) - len(self.dying_RL_agents) < self.num_RL_agents:
            return True

        return False
In native implementation, we can only respawn new vehicle when the total vehicles in the scene
        is less then num_agents. But here, since we always have N-K IDM vehicles and K RL vehicles, so
        allow_respawn is always False. We set to True to allow spawning new vehicle.
        
metadrive/envs/marl_envs/tinyinter.py