Duel

David Mann is a middle-aged salesman driving on a business trip. On a two-lane highway in the California desert, he encounters a grimy tanker truck, traveling slower than the speed limit and expelling sooty diesel exhaust. Mann overtakes, but the truck roars past him and slows down again. Mann overtakes again; the truck blasts its horn and Mann leaves it in the distance.
Mann pulls into a gas station, and shortly after the truck arrives and parks next to him. Mann phones his wife, who is upset with him after an argument the previous night. Several times the truck driver blasts his air horn, seemingly impatient at waiting to be served by the attendant who is attending to Mann. The gas station attendant refills Mann's car and mentions that it needs a new radiator hose, but Mann refuses the repair.




The Peterbilt 281 tanker truck
Back on the road, the truck catches up, overtakes, and blocks Mannâs path each time he attempts to pass. After antagonizing Mann for some time, the unseen driver waves him past indicating it is safe to overtake, but when Mann attempts to pass he almost strikes an oncoming vehicle. Realizing the truck driver was trying to trick him into a collision, Mann passes the truck again, using an unpaved turnout next to the highway.
The truck tailgates Mann at high speeds, forcing him to maintain his speed to avoid being rear-ended. After the truck bumps him several times, Mann drives his car off the road and collides with a fence opposite a diner. The truck continues down the road, and Mann enters the diner to compose himself. Returning from the restroom, he is shocked to see the truck parked outside. Mann studies the diner patrons and confronts the man who he believes is the truck driver; offended, the driver strikes Mann in the stomach and drives away in a different truck. The pursuing truck leaves seconds later indicating its driver was never inside the diner.
Mann leaves the diner and stops to help a stranded school bus, but his front bumper becomes caught underneath the bus's rear bumper. The truck appears at the end of a tunnel. Mann panics, manages to free his car, and flees. To Mann's shock and slight chagrin, the truck push starts the bus and gets it moving. Shortly after, when Mann is stopped at a railroad crossing, the truck pushes his car toward the path of an oncoming freight train. The train passes just in time; Mann crosses the tracks and pulls off the road. The truck passes and disappears. Mann finds it waiting for him further down the road.




David Mann (Weaver) being chased by the truck.
Mann stops at a gas station to call the police and refuel his car. When he steps into a phone booth, the truck drives into it; Mann jumps clear just in time before getting into his car and speeding away, hiding behind an embankment as the truck drives past.
After a long wait, Mann heads off again but finds the truck waiting for him around the bend. Mann stops his car, then attempts to speed past the stopped truck, but it moves across the road, blocking his way. He approaches the stopped truck on foot, but it drives slowly away, keeping just ahead of Mann. He seeks help from an older couple in a car, but they flee when the truck backs up towards them at speed. The truck stops before hitting Mann's car, then waves him past.
Mann speeds around the truck and races up steep grades, putting distance between himself and the truck. He sees a black-and-white car parked on the side of the road, and thinking it is a police car skids to a stop, but finds it is a pest control vehicle. The chase continues up a mountain, but Mann's car begins to overheat when its radiator hose fails. Mann barely makes the summit and coasts downhill in neutral as the truck bears down on him.
Mann spins out and hits a rock wall. The truck speeds toward the car as Mann accelerates, drives up a dirt road, and turns to face his opponent on a hill overlooking a canyon. He places his briefcase on the accelerator and steers toward the oncoming truck, jumping from the car at the last moment. The tanker hits the car, which bursts into flames, obscuring the truck driver's view. The truck plunges over the cliff. Above the wreckage, Mann jumps up and down, laughing with glee and relief, and then sits exhausted at the cliff's edge.

Question: When Mann leaves the diner, he stops to help what?
Answer: A stranded school bus.