Aqui está uma resposta oficial de Robert Kirkman:
- Traumatismo cerebral grave causado pelo acúmulo de acidentes de carro.
- Outro dano cerebral que os matou.
- Já zumbis que foram mortos de alguma forma.
De Glen Mazzara, do The Walking Dead, discute as perguntas mais frequentes dos fãs :
... in Issue 95 of the comic. Robert says, "Any non zombie corpses you saw on the highway either suffered severe brain trauma in a car crash that resulted in that pileup, or had another brain damaging event that killed them. They could have even been zombies in the car for awhile -- until someone came along and killed them."