I'm building a steampunk city, and I wanted to include an underground subway system, where things like goods and people might be transported to different parts of the city. But the logistics of building a steam-powered railway system underground are a bit tricky.
What is the best way to deal with the excess steam? Will there be lines of chimneys rising from the ground above the train tunnels? Is soot from the burning coal going to become a problem eventually? What would the ideal light source be, since electricity hasn't been properly utilized?
Also, assuming late 19th-century steam engines, would the subway system be efficient enough to be practical, taking into account the speed of the trains? Would it be more practical to use it for cargo transport or simply for longer distance travel?
I hope this question isn't too broad to be answered. Thank you!