It's a lose-lose situation. Therefore, as we all know, the proven answer is to flip open your communicator and tell Scotty to beam up all the people tied to the tracks. If you're in command, you don't accept lose-lose situations, unless some expendable engineering red-shirt is in the line of fire.

On a more serious note, these situations are ones that you have to react to rather than think through. Thus, logic is irrelevant. If you had time to think it through logically, any intelligent person would spend that time trying to stop it from happening, trying to save everyone. Eventually, if these efforts failed, then the decision would again be irrational, instinctive. Basically, in a situation like this, your brain is just going to scan through the people in peril and make a snap-judgment... probably based on which person you'd like to have sex with the most, or which is the closest relation...or, maybe if you have strong maternal instincts, which is the youngest. Instinct, not logical morality.

This is also what society would expect a person to do. Anyone that could logically determine the correct moral choice and then act on it, rather than wasting this time trying to save everyone, would not be considered human. Vulcan maybe, but not human.