Originally Posted by jackal

Well, it does matter, because the way UA handles missed Amtrak segments is a bit different. There's a whole thread here: http://www.flyertalk.com/forum/unite...ladelphia.html -- the short of it is that because Amtrak doesn't seem to communicate with United in real-time, downline segments aren't canceled immediately, but eventually they will sync up and there is a good chance the OP will have his return canceled (unless it's an immediate turn and he returns before United realizes he missed his originating Amtrak segment).