In the first case, the tickets are being collected right now, and the train is going nowhere until the ticket collection is complete. It would be the answer to the question, "[w]hat's going on?"
If the collection and subsequent departure were imminent, you would (normally) use will be.
The will have been version would be used when describing the operating procedure; it doesn't imply that a particular train is going anywhere soon. It might be used to answer the question "[h]ow do you make sure there are no freeloaders?"
No comments:
Post a Comment