I didn't mean it to be a critique of the concept of subsumption itself, only your specific example. For instance having the train avoidance system provide a ref

I didn't mean it to be a critique of the concept of subsumption itself, only your specific example. For instance having the train avoidance system provide a reference speed to the wheel controllers seems solid. Having the station stopper create fake trains (or having the train avoider create fake stations) does not seem robust. Would be better to have the station stopper set reference speed, and give the train avoider the authority to override it.