I think that the tunnel and the underground "Penn Station" are seen as normal environment by the UE4, where the same conditions prevail as outside. So when there is fog outside then there is also fog inside. But if we were physically correct, then the tunnel and the underground station should have built-in ventilation shafts, like in underground garages, to regulate ventilation or in the event of a fire. So the tunnel or underground section has to be seen as a different environment, then the rest of New York or Long Island. That would be my suggested solution.The Bakerloo-Line is structured similarly, but does not have the problem.
