In Los Angeles, SWAT Officers Jack Traven and Harry Temple are trying to stop a ruthless criminal, Howard Payne. Payne is seeking to extort millions for a group of hostages trapped in a elevator that is only being held up by the emergency brakes. A bomb is attached to the emergency brakes and unless the city doesn't pay him, Payne will detonate the bomb and cause the elevator to fall.
Jack decides to take the hostages out of the equation and uses a nearby crane to keep the elevator from falling. But Payne has also rigged microphones to keep him appraised of what is going on. Realizing that the police are up to something, Payne triggers the bomb; sending the elevator plummeting to the ground.
Fortunately, the crane holds the elevator long enough for the police to safely extract the hostages. Meanwhile, Jack and Harry realize that the bomber had to hear them rigging the crane and that means he is nearby, possibly in the building itself. Investigating, they stumble across Payne who takes Harry hostage, threatening to blow both of them up unless Jack lets them go. However, Jack decides to take Harry out of the equation by shooting Harry in the leg, forcing Payne to release him. As Jack demands Payne to give him up, the mad bomber seemingly commits suicide in an explosion rather than be arrested.
Afterwards, Jack and Harry are awarded medals and are celebrated heroes. The next day however as Jack is going into work, a bus explodes just a few feet away from him. Horror struck, Jack is then contacted by Payne who is still alive who demands a new ransom. There is another bomb on a bus which will arm itself once the bus hits 50 miles per hour. If the bus drops below 50, it will detonate or if Payne sees the police even try to unload any passenger, he'll detonate by remote control.
Racing through traffic, Jack is barely able to leap onto the bus which has already passed the 50 mph mark from a moving car. Trying to keep the passengers calm, Jack attempts to keep the bomb a secret while simply alerting the driver to the situation. A gangbanger panics when Jack shows the passengers his badge and believing that Jack is here to arrest him, pulls out his revolver and demands to be let off. One of the passengers, a construction worker Ortiz tries to intervene by jumping the gangster. In the ensuing struggle, the gun goes off and wounds the driver; forcing another passenger, Annie to take over driving.
As Annie frantically begins to slow down the bus, Jack is forced to reveal that she cannot slow down, else the armed bomb will explode. But when they run into a traffic jam on the freeway, they are forced to divert into the city where the bus is forced to evade numerous pedestrians, oncoming cars, and even baby carriages. The police are able to clear a route for the bus to a deserted stretch of freeway and both Annie and Jack start to bond over their mutual experience.
Meanwhile, a frustrated Harry is baffled as the bomber has no criminal record, plus no recognizable modus operandi which is unusual; not to mention that he seems to know police procedures and tactics, including how the police dispose of bombs. Harry then comes to a startling conclusion and demands that they conduct a new record search for retired cops with training in explosives.
Meanwhile Payne who is watching live reports from news copters becomes angry when he sees the police ferrying a large flatbed to try and unload the passengers and calls Jack. Jack is able to convince Payne to allow them to unload the wounded bus driver as an "act of good faith" to the bureaucrats. Payne agrees and they are successful in transferring the bus driver over to the flatbed. But one of the passengers, Helen attempts to escape and Payne activates a secondary charge that causes her to fall and is pulled under the wheels of the bus, killing her.
As the grieving Jack, Annie, and the passengers struggle to recover from the shocking and brutal death of Helen; the police are taken aback when they learn that the freeway is unfinished and there is a 50 foot spanning section missing. Unable to remove the passengers, Jack decides to gamble that with the incline and increased seed, they might be able to jump the bus over the gap. Spectacularly, the bus makes the leap and successfully lands on the other side. Once over, they are able to drive into LAX, the Los Angeles International Airport which is restricted airspace and thus forbidden for the news helicopters to enter. Payne calls Jack to congratulate him on his success and wanting an update about his ransom demand. Jack convinces him that he needs to talk to his superiors directly to convince them to release the money and overrules Payne, claiming that he wasn't a passenger so he doesn't fall under Payne's rules.
Jack's superior, Lt. McMahon wants to remove the hostages now that the news copters are no longer overhead but Jack refuses, convinced that Payne will know somehow. Jack then tries to disable the bomb, using a wheeled dolly with a cable attached to a truck to belay himself underneath the bus. Relaying the information about the bomb to Harry, Jack learns that the bomb is booby trapped to detonate if they attempt to disarm it.
Harry successfully identifies the bomber as Howard Payne, a retired Atlanta police officer and former member of the bomb disposal squad. Payne was forcibly retired when a small charge exploded, costing him part of his hand. Finding out that Payne has a local address, Harry immediately rushes out to try and apprehend him and his remote control.
However, before Jack can be reeled back in; the dolly runs over some debris from the bus' damaged tires and swerves out of control, causing the attached cable to snap. Jack is forced to cling to the underside of the bus when the dolly is crushed beneath the tires and is being dragged to his death. Rushing to his aid, the other passengers including Ortiz manage to open up the access panels on the floor of the bus and pull Jack up.
Meanwhile, Harry and a SWAT team have broken into Payne's home and trigger a booby trap bomb; killing Harry.
Receiving a phone call, Jack is hopeful that Harry has good news for him only for a gloating Payne to inform him that Harry is dead and how he's smarter than Jack before demanding his ransom before hanging up. Jack flies into a rage and is comforted by Annie. Hugging her, Jack suddenly notices Annie's Arizona University sweatshirt and recalls that Payne jokingly referred to the driver as a "real wildcat behind the wheel". Realizing that Payne must have seen the logo of the Arizona University which is the home of the Wildcat football team, Jack realizes that Payne is watching them via a security camera that is broadcasting a live video feed of the bus. Jack secretly radios his information to McMahon who commandeers one of the news vans to tap into the feed and creates a fake loop to fool Payne. With Payne blind, the passengers are safely unloaded and the bus subsequently explodes.
When Payne calls for instructions of the ransom drop off, Jack and the police realize that he still thinks that the hostages are still trapped aboard the bus and decide to set a trap for him. Putting the ransom in a sack loaded with a tracking beacon and paint bombs inside, they drop it in the designated spot; a public garbage can and wait. But the canny Payne realizes at the last minute that he is watching a loop. Dressed up as a police officer, Payne is scouting the ransom drop off point, blending in with the crowd when he spots Annie being treated by a paramedic nearby. Walking over to her, he convinces her that Jack send him to escort her to a place of safety.
Jack becomes alarmed when no one has approached the money at the deadline time and demands that they switch the tracker on. They are all shocked when the tracker indicates that the money is in motion and Jack runs out and discovers that a hole has been cut into the bottom of the garbage can and a corresponding hole leading to a maintenance tunnel beneath the street itself.
Dropping into the maintenance tunnel, Jack discovers a tearful Annie who has a vest loaded with explosives being forced by Payne with a handheld remote detonator to help him. Jack tries to have Payne release Annie but Payne sadistically refuses and seizes control of a subway train to escape. Payne then handcuffs Annie to a railing and informs her that unfortunately to cover his escape, he will be detonating the vest with her in it.
Jack jumps aboard the train and unable to approach Annie and Payne directly, climbs to the top to try and take Payne by surprise. But Payne hears Jack and confronts him and the two engage in hand-to-hand combat. Payne is getting the upper hand as Jack is afraid that Payne will release the trigger to the remote detonator. At the last minute, Jack pushes Payne so that an oncoming low hanging signal light decapitates him and Jack is able to seize the remote detonator without triggering it.
Removing the explosive vest from Annie, Jack overhears a radio transmission from McMahon warning them that the subway track is unfinished and that they need to stop the train. However, when Payne killed the driver, he also shot up the controls and they are unable to slow down and he cannot break the railing or Annie's handcuffs. Gambling that he can force a derailment, Jack speeds the train up and the train crashes and grinds to a halt with Annie and Jack alive and safe. As hundreds of tourists come to stare at the crashed subway train, Annie and Jack start kissing passionately.
- Keanu Reeves as Jack Traven
- Dennis Hopper as Howard Payne
- Sandra Bullock as Annie Porter
- Joe Morton as Lt. "Mac" McMahon
- Jeff Daniels as Harry Temple
- Alan Ruck as Stephens
- Glenn Plummer as Jaguar Owner
- Richard Lineback as Norwood
- Beth Grant as Helen
- Hawthorne James as Sam
- Richard Schiff as Train Driver
- Carlos Carrasco as Ortiz
- David Kriegel as Terry
- Natsuko Ohama as Mrs. Kamino
- Daniel Villarreal as Ray
Screenwriter Graham Yost was originally inspired by the 1985 movie Runaway Train but felt if the movie centered around an out of control bus would be more compelling and as a homage to the movie's inspiration, added the last section involving a subway train out of control as well.