My guess is that the present continuous is used in the first clause because it is one way of talking about the future when it is already fixed or arranged, for example, you have arranged to go somewhere or meet somebody "I'm leaving next week. I've booked my flight" or "What time are you meeting Mary this evening?".
That could be the case, yes. Or it could be that the speaker is talking while the action of taking the train is currently in progress at the time of speaking. Without any useful context, we just can't know, which is why context is so important to reveal the meaning (the aspect) inside the mind of the speaker.
In future, for any sentence you study, think carefully about:
- what the situation is
- who is speaking
- to whom it said
- what the speaker is trying to do with the utterance
All of these things count as part of the meaning/use of the utterance. You usually need to understand all of these things in order to understand the utterance fully. From now on, please don't offer uncontextualised sentences. Thanks.