Nautical is an adjective derived from the Greek word for boat. So the problem is there is no Greek word for train to draw from. locomotive, as a Latin-derived term, makes some sense here. The effort at ferroequinos above is similarly motivated, modern English loves to use Greek or Latin to make adjectives.
So I think you may need to make up a new word to capture the whole complex. Is there a king or God or inventor whose name could be turned into an adjective, someone people would naturally associate with trains? I order to make a new word stick it has to make some natural sense to people.