I hear this announcement often at the train-station. Is this grammatically correct, without an 'is' after the word 'train'?
It's fine for train-station announcements and the like. A form of ellipsis. Means dropping some syntax. Got it?
ellipsis |iˈlipsis| noun ( pl. -ses |-sēz|) the omission from speech or writing of a word or words that are superfluous or able to be understood from contextual [NOAD]
Just don't use this particular form of ellipsis in formal writing and you should be fine.