The Texas Chainsaw Massacre: The Beginning

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In 1939, a woman dies while giving birth in a slaughterhouse, and the manager disposes the baby in a dumpster. A young woman, Luda Mae Hewitt, finds the child while searching for food. She takes him back to the Hewitt residence, names him Thomas, and decides to raise him as her own.
Thirty years later, Thomas works in the same factory in which his real mother died, working for the same man who left him in the dumpster. He is informed that the plant has been shut down by the health department, but refuses to leave until the boss forces his assistant to make him leave. Later, Tommy returns and brutally murders his boss. Before leaving, Tommy finds a chainsaw. Luda Mae's son, Charlie Hewitt, learns from the town's Sheriff what Tommy has done and accompanies him to arrest him. When they find Tommy, Charlie kills the Sheriff and assumes his identity. He takes his body back home and butchers him for stew meat. He informs the rest of the family that they'll never go hungry again.
Two brothers, Eric and Dean, are driving across the country with their girlfriends, Chrissie and Bailey, to enlist in the Vietnam War. At a diner, they meet a female biker named Alex, who later follows them. Dean reveals he's decided not to enlist and burns his draft card, right before Alex draws a shotgun and orders the group to pull over. A chase ensues and the car crashes; Chrissie is thrown from the Jeep and lands in a field out of sight. Hoyt arrives and immediately shoots Alex.
Hoyt finds Dean's burnt draft card and demands to know who it belongs to. To save his brother, Eric claims that it's his. After making them put Alex's body in his car, Hoyt forces the group in as well, and calls for Uncle Monty to tow the wreckage, which Chrissie is hiding in. Hoyt drives them to the Hewitt house and has Tommy butcher Alex's body. He then hangs Eric and Dean up by their arms from rafters in a barn, and ties Bailey under a kitchen table inside the house. Monty brings the wrecked car back to the house, and Chrissie sees her friends from afar. She runs back to the highway to get help and flags down Holden, Alex's boyfriend, who follows her back to the house.
At the house, Hoyt wraps Eric's face with cellophane, slowly suffocating him for trying to dodge the draft. Dean begs him to stop and admits the draft card was his. Hoyt allows Eric to breathe and releases Dean, promising to let them go free if he can do twenty push-ups. He does so, but Hoyt beats him with a baton, leaving him incapacitated. When Hoyt leaves, Eric breaks free from his restraints and gets Dean to safety before sneaking into the house to free Bailey. However, Dean is caught in a bear trap and Hoyt knocks Eric unconscious. Bailey escapes in Monty's truck, but Tommy stabs her in the shoulder with a meat hook and drags her back to the house. He carries Eric to the basement, where he sees Alex's mutilated body hanging from the ceiling.
That night, Holden and Chrissie arrive at the house but part ways to search for their friends separately. Chrissie finds Dean, who informs her Eric and Bailey are still inside. Holden encounters Monty and shoots him in the knee before taking Hoyt hostage, and ordering him to take him to "the girl". Meanwhile, Chrissie hears Eric screaming and finds the basement door. Hoyt takes Holden to Bailey, incorrectly thinking she is the girl he's looking for. He calls Tommy for help and Chrissie enters the basement unnoticed. Holden prepares to kill Hoyt but Tommy arrives and kills Holden with the chainsaw. Chrissie finds Eric but is unable to free him, and hides when Tommy returns. Tommy inspects Eric's face before impaling him with his chainsaw. He skins Eric's face and wears it as a mask.
Chrissie is about to flee when she hears Bailey's screams and decides to go back and save her. She finds her upstairs but Hoyt catches her and brings her downstairs for dinner, along with Bailey and an unconscious Dean. Leatherface slits Bailey's throat and tries to take Chrissie to the basement, but she stabs him in the back and jumps out of a window.
Dean regains consciousness and beats Hoyt before heading off to find Chrissie. Chrissie enters the slaughter house, and after noticing that Leatherface has tracked her, she grabs a knife and hides. She cuts Leatherface's face when he finds her but he overpowers her. Dean arrives as he is about to kill her, but Leatherface kills him with the chainsaw. Chrissie finds a car and drives off. She sees a state trooper in the distance, but as Chrissie pulls over, Leatherface appears in the back seat and impales her, causing her to lose control and run over both the trooper and the man he pulled over. Leatherface then exits the car and walks along the road back towards the Hewitt house.

Question: Who runs back to the highway for help?
Answer: Chrissie