Move Forward, Move Forward

When the world ends, I will be the only one left alive. Zombies are rampant, ice and snow are devouring all civilization, and I am in a steel fortress called "Forward" - a thousand-meter-long train, covered with armor enough to isolate the apocalypse, and eternally driven by a nuclear power cube taken from an aircraft carrier. The train is controlled by a silent AI, passing through frozen ruins and waves of corpses day after day. It has it all: fully stocked carriages, climate-controlled accommodation, and the safety of a tomb. But I don't know why I'm the only one left on this roaring boat; let alone whether there is a second heartbeat on this planet beyond the railway tracks. There is only one question, as the endless ice field repeatedly runs through my mind: When you are the only "safe" person in the apocalypse, is safety a gift or the longest prison sentence?