Except, given finite resources, the tracks would run out before having enough space for 8 billion tied-up people.

Yes, say there are 2^33 people for illustrations sake, by 33 decisions you (the first puller) are guaranteed to be dead too. At 32 it's 50/50, the odds increase as the decisions get made. From a self preservation standpoint the best thing you can do to minimize your personal risk is pull the lever. It also happens to kill the fewest other people.

The only out is nobody pulls the lever.