Killer in the Backseat (also known as High Beams) is a common urban legend in the United States and the United Kingdom.
The legend involves a woman who is being followed by a strange car or truck. The mysterious driver flashes his high beams, tailgates her, and sometimes even rams her vehicle. When she finally makes it home, she realizes that the driver was trying to warn her that there was a man (a murderer, rapist, or escaped mental patient) hiding in her back seat. Every time the man sat up to attack the driver, her pursuer scared him.
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. Inside the station, he asks if she knows there's a man in her back seat. In another she hits something, stops then the man gets in the back. Also one where she stops at a house, get a man with a shotgun who goes to kill the driver who followed to be told about the man in the back of the first car.
The story is often told with a moral. The attendant is often a lumberjack, a trucker, or a scary-looking man; someone the driver mistrusts without reason. She assumes it is the attendant who wants to do her harm, when in reality it is he who saves her life.
The 1998 film Urban Legend begins with this scenario.
The 1st segment, Terror in Topanga, of the 1983 film Nightmares is a depiction of this legend.
An episode of Jonathan Creek begins with a version of this legend, except instead of a killer inside the car the pursuing driver was trying to alert that there was a body tied to the back of the car.