When she finally makes it home, she realizes that the driver was trying to warn her that there was a man (a murderer, or escaped mental patient) hiding in her back seat.
Each time the man sat up to attack her, the driver behind had used his high beams to scare the killer, causing him to duck back down.
[3] In some versions, the woman stops for gas, and the attendant asks her to come inside to sort out a problem with her credit card.
The story has been identified as circulating at least as early as the late 1960s, and may have gained more widespread recognition after appearing in a letter to advice columnist Ann Landers in 1982.
[4] It has been speculated, including by Snopes founder David Mikkelson, that the legend may have been inspired by a vaguely similar case which took place in 1964, in which an escaped murderer hid in the backseat of a car, only to end up shot by the car's owner, a police detective.