The conductor can radio the engineer to stop the train, and he could do so pretty much whenever the heck he darn well wants to, and the FRA has nothing to say about it.
That was pretty much my understanding too.........
Doesn't an engineer up and stopping, unexpectedly and unplanned, the train cause "traffic" kinds of problems with any trains coming the other way (single track) and and trains coming from behind?
It depends on the situation.
*How long is the train stopped? Is it just to reset a switch on the locomotive for a couple of minutes? Is it because of some other defect that might take 10-20 minutes to fix? Maybe much longer?
*Is the line single-tracked, or are there multiple main tracks?
*How much other traffic is on the line?
Keep in mind, I'm not saying that any conductor or engineer will just stop the train for the hell of it. They want to get where they're going as quickly as they can, too. But if they feel the need, for whatever reason, to stop the train, they can. Every rule book out there basically says just that.
If you're out there on the main and you're going to be stopped for more than a brief period, it's a good idea to let the dispatcher know that you're stopped and why. A passenger train that's just going to make a brief unscheduled stop to let someone off (say, for example, if someone left something on the train, went back to get it, and the conductor highballed the train while the passenger was still picking up the item, the conductor could just have the train stop at the next safe location, such as a commuter platform where they normally wouldn't stop) probably wouldn't even bother the dispatcher with the call.
To get back to the point made earlier, in the case of an Amtrak train making an unscheduled stop, the conductor only has to document on the train's delay report the reason the train didn't make the scheduled run time from A to B. If the stop isn't too long, and the reason is legitimate enough, Amtrak will not complain to the conductor, nor will the host railroad.