To provide some context for this story, I used George A. Romero's 'Night of the Living Dead' as a jumping-off point for the world-building.
The zombie apocalypse started in 1968, which means humanity never went to the moon. There is futuristic technology, but it's relegated to certain vehicles with restricted access.
The Roamers in the story are sort of a natural extension of the Dead Reckoning vehicle from 'Land of the Dead.'
(There will be other nods to Romero's films later down the line ;))
I also used the original term 'ghouls' instead of 'zombies' (Though I like to think that each culture from the various Zones has its own terminology for the living dead).
Oh, and 'Corpse Planet' takes place on October 8, 2714 CE.