A trailer carrying 180 bales of alfalfa overturned Tuesday on southbound Interstate 5 in Chula Vista.
The truck's driver was heading home to a South Bay ranch at 8 p.m. when he was struck by an out-of-control Mustang, CHP officials said.
The force of the impact flipped the trailer onto its side on I-5 near E Street.
The Mustang was traveling at speeds close to 100 miles per hour according to witnesses.
The Mustang's driver wasn't under the influence according to investigators, but may face charges at a later time.
No one was hurt.
CHP issued a Sig Alert while crews loaded each bale of hay onto a flatbed by hand.