Jeremiah Hartline claims he swerved from side-to-side across the road in an attempt to shake off the living dead creatures clinging to the truck.
The 19-year-old allegedly stole the 18-wheeler lorry, carrying a load of strawberries, after hitching a ride with truck driver Daniel Martinez in Tennessee.
When the trucker got out of the vehicle at a weigh bridge, Hartline says he began to hallucinate that zombies were coming after him and accelerated onto the highway.
The teenager collided with several cars, causing a pile up which injured seven people, before flipping the big rig on its side, blocking the carriageway for three hours.
Two people were badly hurt in the crash, including a 19-year-old woman who remains in hospital after suffering a serious head injury and severed artery.
California Highway Patrol Office Nathan Baer said: “He was arrested at the crash scene and appeared to be in an altered state, claiming he was being chased by zombies.
“Hartline swerved the truck side to side to shake the zombies off."
Hartline, from Tennessee, pleaded not guilty to six offences, including assault with a deadly weapon.
He also denies reckless driving, vehicle theft, attempted vehicle theft, driving without a licence and involvement in a hit-and-run resulting in injury.
He is currently being held on $500,000 bail at the Southwest Detention Center in Murrieta, California.
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