That is an unscheduled freight train pulling out. Those white flags are still used today.

I recall engines carrying green flags too. They meant that there were "extra sections to follow." This occurred when a train was not sufficient in length to carry all the passengers or freight. The railroad would break it up into 2 or more trains(sections) as necessary. The green flags would be a visible warning that there were other trains to follow sometimes only minutes apart. Each engine would carry the green flags except the last which may display the white flags for "running extra."

The exact usage may vary from RR to RR, but these rules were, for the most part, universal.

Wow, absolutely amazing. It could have been taken yesterday. If only you could have seen a scene like this yesterday though.

I'm not sure what exactly it is in that picture, but it gives me a visceral feel of deep biting cold in a way that few others do. Maybe it's the clear blue of the sky and the way the clouds from the engine are just hanging there, and the dry dry snow, or maybe it's remembering the time when I was in Chicago on Thanksgiving with a totally inadequate coat waiting an hour for a bus that had been rerouted, but ... brrr!

...in Chicago...in December...brrrrr.

This would be a tough time to be a brakeman. Look at the way the smoke just hangs in the frigid air. Where's my parka, I suddenly have a chill!

This is beautiful. I grew up within earshot of these yards, and remember lying in bed on summer nights, listening to the trains.