I should also point out the serious cloggage to train traffic if they used that MRL/UP connection at Sandpoint. Normal operations have UP southbounds calling BNSF for a signal to proceed across the Sandpoint diamond. If BNSF has two or more of its own trains lined through there, the UP train will typically hold on the north side of town, off the crossings, until he's told to come down.

Now, if a UP detour off MRL were to use that connection, he'd need a roughly one-hour hole in BNSF traffic to do it. First, pull west part way onto BNSF, head end west (geographically south) of Sandpoint Jct. Then back through the connection. Then southward on UP, across the BNSF diamond. They wouldn't want him to wiggle through the connection and then sit on the crossings for a fleet of BNSF trains. It would have to be an all-or-nothing move. I doubt BNSF or MRL would tolerate that kind of blockage happening four, five, or more times per day.