This would probably play hell with frame rates but the current smoke effects tend to just vanish as you pass under a bridge or tunnel. This is especially noticeable now we have the steam on Peak Forest with several long tunnels. Not only should you get the “bursting” effect as the train leaves the tunnel, the aftermath of a steam loco working hard should leave a thick haze of smoke in the tunnel that only slowly disperses via the portals and vent shafts. To a lesser extent you are going to get this with diesels too. So it would be great to see more realistic smoke etc. effects implemented where structures are concerned.
as much as this would murder the framerate (as you mentioned), I would LOVE to see this come to the game
I can live without this due to having ridden more than once through the Moffat Tunnel on the California Zephyr. They cut off the outside air due to the tunnel's length, but the train still smells like diesel exhaust by the time it emerges.
Most UK tunnels rely on passive ventilation, i.e. through shafts or just drifting out the portals. One of the reasons in steam days crews hated working through long tunnels, or tight bores like Combe Down and Devonshire Tunnels on the S&D climbing up the 1 in 60 gradient from Bath Junction to Lyncombe Vale.
