Not necessarily about Baltimore only, but many operations besides Train Operations occur. I recognize 161.505, I believe, as a frequency used on NS by shop forces and MW. You have to remember that there is MUCH more going on on railroads besides "choo choos" and trains! LOL!
Bridges and Buildings/Structures, etc use dedicated RR frequencies as well. Then there are "housekeeping" chores, and supervisors in charge of maintaining camp and kitchen trailers---all may make use of dedicated channels. Others such as Materials Management have frequencies of their own as well, but can operate on the "road" channel when needed The idea is to separate Operating from non-Operating tasks and prevent interference.
One of the
HARDEST things I have found is to get people to grasp that railroads are NOT "all about trains" and the running of them alone. Sure, this is the primary reason for their being. But everybody seems to think that there is NOTHING else BUT the trains. Only when one actually works in the industry does he realize just HOW diversified railroads ARE when it comes to all the support and logistics that go to make that train run!
Gadfly