I can see why the MTA wouldn't want you telling people to go to a track before it is actually assigned -- if the train ends up on a different track, now you need to get all those people back up, off that platform an on to the new one, clogging stairs that that people who actually wanted that platform might be trying to use too. Obviously it would be nice to assign tracks earlier, so that people can head straight to the right platform, but sending people to potentially the wrong platform seems even worse.<p>EDIT:
Penn is extremely platform/track constrained -- NJ Transit, LIRR and Amtrak are all sharing a fixed number of platforms, some of which are too short.<p>To maximize platform utilization, they have to wait until the last minute to finalize track assignments -- if you reserve one too early and the train ends up late, you're wasting an empty platform. Once you send a horde of people to a platform, moving them to a different one is a challenge (stairs/bottlenecks, communication, etc).