Shortlines, Industries, and Empties

[dave1905]

So pool cars are in captive service and general service cars can be used as the railroad sees fit?

They are captive in that they serve one origin or destination or one company's origins or destinations. So a covered hopper in a plastic pellet pool could serve one chemical plant and a thousand destinations or a power plant's coal train could load at a dozen mines and serve one power plant or another power utility could load coal at a dozen mines and unload it at any one of their four power plants.

General service cars are used as the railroad sees fit, subject to the AAR car service rules.