So which part of the Moral Argument is it pertinent to? The substantiation of premise1, premise2, or the conclusion?
Now, what´s the correct answer according to your "objective morality"?
So you aren´t actually asking what you asked ("What should you do?", which asks me to take time to premeditate on the issue) but "What would you do?" (under time pressure, without having the time to think about it)?
That´s not the way I would describe my options, to begin with.
I have answered it. Several of my values are in conflict here - it isn´t called a "moral dilemma for nothing".
In case you actually meant to ask "What would you (under time pressure, without having premeditated on such a scenario, and without the time to do so now)?": I cannot conclusively answer this question until I am actually in that situation, but I can easily fathom myself being paralyzed and unable to make a decision, which would result in the train running its original course.