Switch the track from the bottom to the top as the train is half way over the switch, causing the train to drift across both rails hitting all three tied up people and the second switch operator.

Electrifying the tracks.

Depends on if you're happy with someone else killing lot more people, or if you want to kill someone yourself.

Assuming this goes to infinity, the reasonable thing to do is to kill one person to prevent someone else killing a lot of people. But that would make you directly responsible for killing that person.