There are two corrects answers in this sentence according to the answer keys, but I don't know why and when (like in a certain situation) which one should be used.

Before the train departs, all the tickets --------- collected.

1. are being --correct
2. were being
3. had been
4. will have been --correct

I understand that number 4 is correct if the writer wants to say that tickets will be collected in the future before the train departs. 
As for number 1, under what circumstance is this used? Does the writer want to say that all the tickets are being collected not before the train departs?

Thank you.