Or to take on any other railroad position? I'm thinking about starting to apply further and further away from home. How common is this?
"Booming" used to be pretty common, and now with larger seniority districts, moving out of your currently location means you don't usually have to give up much. I've never moved, but I have been furloughed. When I was furloughed, they offered permanent transfers to far away places like New York and Louisiana. I declined them, because they were permanent, and I would have to have given up the seniority I hired with.
More recently, a friend of mine who was a new-hire couldn't hold any work, so he was able to travel to New York and work for a bit, until he could hold better down this way. He did it without even leaving his seniority district, which just a few years ago, he would have been. It certainly cuts down on the red tape.
Moving a far distance is a big life decision, further made complicated by age, whether or not you have a family, and other reasons. Even if you move to a larger city, or terminal, there is never a guarantee of work. Something to remember. I know of a few folks who have moved between 100 and 200 miles to be closer to work, but I personally have stayed put.