There is a moving train. Someone onboard the train would like the part of the train they're on to be separate from the rest of the train, usually any number of rear cars detached from the front cars being pulled by the engine, which is usually where this person is located. So they decouple the train cars at a chosen point, leaving the abandoned train cars to fall behind while the front part races away.
A person's motive for so doing can vary. Commonly, it's an escape method, but it can also be used in situations involving a physical danger onboard the train, such as the locomotive becoming uncontrollable, or dangerous cargo. It could also be a means of sabotage, to capture or steal something in the back part of the train. And, if the separation occurs on a particularly dangerous part of the tracks, it can be a form of murder by Runaway Train. But this trope covers any situation where rail cars are separated from a moving train.
In real life, this is unrealistic when applied to modern trains, as decoupling cars while the train is in motion will also disconnect the brake pipes, bringing the detached car to a screeching halt (although not instantly, thanks to momentum and the mass of your average train car, and also brakes not working instantaneously).
Compare Emergency Cargo Dump, where a character tosses cargo out of their vehicle to make it weigh less to go faster and/or avoid sinking.
- Ace Attorney: An original story for the anime involves the separation of the cars of an operating train in order to rearrange them mid-journey. The reason for this was it was to move the dining car, from the middle of the train to the back, as the train's owner planted a bomb there as part of a suicide plot. He was an escaped convict who didn't think he would get a fair trial, so intended to die without endangering the rest of the train's passengers.
- Dragon Ball Super: Train robber Pasta Macareni attempts to escape from the galactic patrol by detaching the train cart their pursuers are on, diverting it to a different track and blowing up the track they're headed to. Unfortunately for the robbers, their pursuers can fly.
- One Piece: The sea train mini-arc between Water 7 and Enies Lobby sees this being used several times by the Straw Hats as they try to retrieve Robin from the head cabin of the Puffing Tom. The first time it works like a charm, letting them eliminate fifty-odd Mooks without breaking a sweat; the second time, unfortunately, one of their enemies turns out to own whips strong enough to hold the cars together in lieu of the steel links. And then it turns out another of their enemies can teleport.
- Soul Eater: During the runaway train arc, Kid, Liz and Patty find themselves in a Mêlée à Trois against one of the Mizunes (Working for Medusa) and Fisher King (working for Arachne) to get to the key of the train that keeps it running. Kid and Fisher King manage to make their way onboard and have to stay ahead of the Mizune who uses her whiskers to slice up the cars. Fisher King gets ahead and uncouples the car to try and shake them off...except in the confusion he didn't jump to the car that was still attached to the engine and has to use his fishing rod to reel himself to it. Kid likewise manages to get on by having Liz, Patty and him grab each other's ankles and sling themselves to the car.
- In the DOMA arc of Yu-Gi-Oh!, the part of the train that Jonoushi, Honda, and Anzu are riding on gets separated from the part of the train that Yami Yugi is on due to Dartz's magic.
- An expansion for Colt Express has an "unhook the carriage" event card, which detaches the last carriage of the train and all players in the last carriage must jump to the next carriage.
- In the graphic novel Calamity Jack (the sequel to Rapunzel's Revenge), the protagonists are aboard a train when it is attacked by massive, hostile ant-creatures. They quickly usher the passengers into the front car and disconnect it, with Jack staying behind to fight the monsters while the civilians escape.
- In The Black Island, Tintin is pursuing the bad guys on a train, but they uncouple the car between him and them, allowing them to escape.
- In Prisoners of the Sun, Tintin and Captain Haddock find themselves on a runaway coach while travelling by train on the way to find Calculus. The stationmaster at the next station then mentions it was the first accident on the line, but by that point Tintin is already convinced it wasn't an accident at all (he learned the hard way that the emergency brake had been sabotaged).
- Anastasia: Demons summoned by Rasputin separate the cars from the train where Anya, Dimitri and Vladimir are travelling, then destroy the bridge ahead in an attempt to kill them.
- This happens in Inside Out when Honesty Island collapses as a result of Riley stealing her mom's credit card, as the Train of Thought is still in motion when it happens. Only the car Joy, Bing Bong and Sadness are in doesn't fall into the memory dump like the other ones did.
- Phineas and Ferb the Movie: Across the 2nd Dimension: Second dimension Candace detaches the a minecart with the first dimension heroes inside so she, her brothers and the other resistance members can escape from the robots chasing them.
- The cold open for Suicide Squad: Hell to Pay has the team confronted by White Whale's guards while on a train. Jooley uses her laser gem to cut the car they're in in half, separating the train and letting the squad escape the mooks and proceed with their mission.
- Breakheart Pass: A train carrying U.S. Army troops is going up a mountain. Villains aboard the train detach the cars carrying the troops, which begin rolling back down the mountain. The cars crash, killing all of the troops.
- The Cassandra Crossing has the passengers onboard a European train get exposed to an artificial contagion. Rather than treat the victims, the United States military decides to dispose of their indiscretion by quarantining the train, sealing the passengers inside, and routing the train toward the Cassandra Crossing. Shots of this old iron railroad bridge show that it has turned to rust and decay, and couldn't possibly support a train anymore. The desperate passengers struggle with armed guards to uncouple their cars from the rest of the doomed train.
- The Green Hornet Serials: The gangsters in the first serial intend to uncouple the freight cars used by a shipping company to put financial pressure on that company to sell out to the gang. To boost the pressure, they intend to uncouple the cars once the train gets into the hills (rolling back with no brakes = decent chance of a derailment and destroyed instead of just late shipments) After the Hornet interferes, the caboose he and a gangster are in gets detached from the moving train to set up a Cliffhanger.
- Silver Streak: On a runaway AmRoad train, the passengers separate the locomotive from the cars in an attempt to slow it down.
- The Train, set in occupied France, has Resistance members uncouple the cars on a train full of stolen artwork while they are in motion and stage a series of crashes to prevent the Germans from simply replacing the locomotive and keep the cars stuck in one location.
- Shanghai Noon: After Chon Wang fights with Roy O'Bannon's gang, one of whom shot and killed his uncle, he uncouples the cars from the tender, leaving them stranded.
- In Solo: A Star Wars Story, the Train Job involves decoupling the cars filled with coaxium.
- Breakheart Pass: A train carrying U.S. Army troops is going up a mountain. Villains aboard the train detach the cars carrying the troops, which begin rolling back down the mountain. The cars crash, killing all of the troops.
- Raising Steam has a train under attack by hardline Dwarfs, who try to detach several coaches so they can deal with the people inside then at leisure. Unfortunately a Troll policeman sees the danger and physically holds the severed section to the main train as the coupling is broken; he becomes a living coupling until the danger is past.
- Sherlock Holmes: The Seven-Per-Cent Solution has the wicked Baron von Leinsdorf in his "special" (a train not normally scheduled on that track) find himself pursued by another locomotive. The Baron orders the last car on his train detached, aiming to make it an obstacle to his pursuers. The engineer on the chasing locomotive is an old hand, however, and he neatly couples the stray car onto his locomotive. In fact, this newest car gets dismantled for boiler fuel by the heroes, which had been running low at that point.
- Banacek: in "Project Phoenix," a flatcar is switched out of the middle of a moving train, onto a very temporary spur, by breaking the train both ahead of and behind the car, using a cable and a winch. No word on how they prevented this double break from triggering an emergency air brake application, or how they kept the engineer from seeing the temporary spur.
- Doctor Who: In "Nikola Tesla's Night of Terror", the Doctor gets rid of a mysterious figure chasing her, her companions, Nikola Tesla and his assistant on a train after separating him from his weapon by pulling the bolt out of a coupling, leaving the attacker on the back half of the train as the rest speeds on to New York.
- Shining Time Station: In "Queen For a Day", as part of their plan to steal the Queen's jewels, a pair of thieves named Biff and Bull uncouple the Queen's coach from the train pulling it. This results in the coach with the Queen herself and her grandson, Prince Mickey ending up lost in Indian Valley.
- Discussed in The Adventure Zone: Balance in the last episode of the "Murder on the Rockport Limited" arc, as a possible way to deal with the Runaway Train; Merle asks if they couldn't just disconnect the locomotive car from the rest of the train. Graham shoots that down; yes, they could, but the locomotive would still crash, and while it wouldn't be as bad as the entire train crashing into the Neverwinter station, it would still cause a lot of damage and possibly get people killed.
Merle: Have you met us?
Taako: That's some other D&D game's problem!
Merle: Yeah! Let 'em fix—
Griffin: [cracking up] Wait a minute, wait a minute: "You have safely brought the princess back to her chambers in Neverwinter after besting the nineteen dragons of the Horrid Rim and—OH FUCK, A TRAIN!!! OH MY GOD NO A TRAIN JUST RAN INTO—oh, God, no. Oh Jesus."
Merle: We'd be safe!
Taako: I'm just living out my lifelong dream of reenacting the end of Silver Streak. It's all I've ever wanted.
- In the Animaniacs Licensed Game for the Sega Genesis, the second half of Stage Three, which takes place on the stage of a Western film has the Warner siblings board a train to escape from Ralph, who is chasing them down. When the Warners get to the engine at the end of the stage, they uncouple it from the freight cars it's pulling, leaving Ralph who is on them, behind.
- Assassin's Creed: Syndicate: Players can decouple cars while trains are in motion.
- Final Fantasy VI: When Sabin, Shadow, and Cyan are being pursued by the ghostly passengers of the Phantom Train, they decide to disconnect the car the passengers are on to lose them.
- Final Fantasy VIII: La Résistance group the Forest Owls plan to kidnap President Deling of the Galbadian Empire by disconnecting the cars of the train that's bringing him to Timber and using a train of their own to steal his private carriage. It appears to work at first, but the "president" they kidnap is actually a Body Double.
- Grandia: Justin and co escape from an enemy base by train, and then disable the engine controls, lure their pursuers into the engine, and disconnect the engine from a rear car. The car they're in slows to a stop because it's not connected to the engine, while the engine Nina, Saki and Mio are stuck in goes on for several miles before they can safely get out because there's no brakes, giving Justin time to escape on foot.
- Henry Stickmin Series: In one of the options in the Little Nest Egg route, "By Land," Henry detaches the passenger car filled with Toppat members so that he can make off with the train and a car filled with their stolen goods. However, because no one was driving the train (Henry killed the conductor, Mr. Macbeth), it keeps speeding up to the Toppat Launch Site until it crashes.
- Mega Man X4: In the Military Train level, Repliforce soldiers will sometimes blow up the couplings between the train carriages in an attempt to hinder X and Zero's progress through the level.
- Professor Layton and the Diabolical Box: The train the characters ride on to investigate the titular box does a mid route reshuffling in a tunnel to swap one car onto another train. It helps that the passengers are put to sleep using special flowers.
- Resident Evil 2 (Remake): Leon, Clarie and Sherry are beset by a heavily mutated William Berkin who makes his way onto their escape train and up the cars. The character that was used in the A scenario will uncouple the train while the one that was in the B scenario (who likewise will confront Berkin personally) stabs Berkin in the eye and pulled back to where the others are as the uncoupled car falls behind into the flames of the exploding Umbrella complex, finally killing Berkin once and for all.
- In Sonic Shuffle, the fourth board is Riot Train. This board has sections where freight cars can couple up to the train, but also ones where they can uncouple from it. If your player character is unlucky enough to be on one of the freight cars as it uncouples from the train, they'll have to find a helicopter space in order to catch up to the rest of the train, where the Precioustone piece is.
- Star Fox 64: As mentioned in Train Escape, the train conductor on Macbeth will begin detaching cars from the train in order to throw off Fox's pursuit in the Landmaster. However, if Fox hits the eight switches to send the engine car careening into the fuel bunker, the train is now Too Fast to Stop without the extra weight from the other cars.
- Super Smash Bros. Ultimate (and its 3DS/ Wii U predecessor) have a Train map based off of the one seen in The Legend of Zelda: Spirit Tracks. At one point in the battle, the caboose deliberately detaches (and the player's character with it if they're not careful). Other train cars get added on/detached as well.
- Subverted in Syberia II. When Oscar's clockwork train becomes lodged in snow, Kate Walker has to detach the passenger car from the rest of the train, but Oscar waits to start the train until after the job is done.
- Team Fortress 2: In the short film "End of the Line", the RED Scout accidentally uncouples the last car of the runaway BLU train as he boards it in an attempt to stop it from crashing into their base. Even when the train itself is stopped by the Heavy with help from the Medic's ubercharge, the lagging last car nearly becomes the Spanner in the Works as it stops within inches of the explosive depot, narrowly avoiding disaster.
- Vandal Hearts has a stage battle set upon a train. After a few turns, a train car will get decoupled, and anyone still on the decoupled car will be lost for the rest of the battle.
- Madness Combat: Tricky tried to run Hank over with a train in Antipathy. When he realized that Hank not only managed to dodge the train but board it, he then attempted to disconnect the engine from the rest of the cars. It didn't work, because Hank managed to jump between the gap and reach him anyway.
- The Black trailer ends with Blake escaping Adam this way by cutting the coupling in half, with him left behind on the last cars as the rest of the train speeds away.
- In the conclusion of Volume 2, Adam's White Fang faction (who unknowingly are working for the series' Big Bad) are driving an underground train towards Vale. Each railcar contains a bomb, and on their way to Vale, the cars detach one by one, causing multiple breaches when their bombs explode, allowing Grimm to enter through these breaches and giving them a handy access route into Vale.
- At the start of Volume 6, a train on which the heroes are traveling towards Atlas, is attacked by a large group of Grimm. It turns out that the Artifact of Power that they carry with them attracts the Grimm, so any plan they could come up with to keep the passengers safe is basically doomed. In the end, they decide to split the party, with Team RWBY staying behind with the artifact on the last train car to fight the Grimm, and detaching this car so Team JNR can escort the remainder of the train and its passengers to safety.
- Animaniacs: In "Whistlestop Mindy", Mindy strays onto the mail car of a train. When Buttons chases after her, Mindy pulls out the bolt that keeps the mail car coupled to the passenger coach, causing the two cars to separate. Buttons grabs the couplings of the two cars to keep them together and lets Mindy walk across him like a bridge. When Mindy gets to the passenger car, Buttons puts the bolt back in the couplings.
- Dennis the Menace:
- In "Train That Boy", a Spy sneaks onboard the same train that Dennis, his parents, and Mr. Wilson are on so that he can use a bomb to destroy a power plant on the train's route. When Dennis accuses The Spy of being a spy, Mr. Wilson forces him to apologize to him, and Dennis ends up foiling The Spy's attempt to blow up the power plant as a result. The Spy tries to get away from Dennis, who is trying to return his briefcase, not knowing there's a bomb inside it. Near the end of the episode, The Spy uncouples the brake coach from the train to get away from Dennis, but unfortunately for him, Dennis tosses the briefcase at him, and the bomb explodes when The Spy catches it. It also turns out that the brake coach was full of policemen, who arrest The Spy.
- In "Menace of the Mine Shaft", Dennis, his parents, Tommy, and Margaret are on a train taking a tour of a mine shaft. When Dennis comes to a junction, he uncouples his car and he, Tommy, and Margaret go into an Abandoned Mine in search of gold. Near the end of the episode, Dennis, Tommy, and Margaret find their car and get back in it. They meet back up with the rest of the train, which the car couples back up to.
- Jonny Quest: In "Calcutta Adventure", the Quest team is taking a train trip up into a mountain range. Bad guys aboard the train detach the car the Quests are in and the car rolls down the mountain. It jumps the tracks and ends up at the edge of a cliff, but the Quests manage to get off the train car safely.
- The Legend of Korra: In "The Battle of Zaofu", Varrick, who spent the first half of the season performing his energy research aboard Kuvira's personal train (whose rail spans nearly the entire Earth Kingdom), unknowingly discovers the destructive potential of the energy within the spirit vines. When his initial protests against creating weapons utilizing such power (because even he has some standards he won't cross) end up getting him and Bolin forced to continue such research at gunpoint, he creates a bomb set to detonate at a set time (it also has a dead man's trigger in case anyone tries to defuse it, or kill him). After forcing their jailers onto the adjacent rail car, Bolin separates it and their jailers speed away on the side of the train with the engine, as Varrick's research was being performed within the rear of the train. Luckily for both of them, Bolin is an exceptional earth bender, and he and Varrick are able to escape just before the bomb explodes.
- The Looney Tunes Show: In "Ridiculous Journey", Taz, Tweety, and Sylvester are on the run from Blacque Jacque Shellacque, and at one point attempt to escape from him by boarding a freight train. Jacque catches up to them, and chases them to the caboose. Taz bites the coupling between the caboose and the hopper, causing the caboose to roll away from the train. Taz, Tweety, and Sylvester escape from Jacque, but the caboose rolls down the mountain and sinks into a river.
- Milo Murphy's Law: In "The Undergrounders" this happens to the subway car that Milo, Zack, and Melissa are travelling in to get to the museum. The rest of the class is in the previous car and know Milo well enough to be unconcerned about him and his friends.
- In the Muppet Babies (2018) episode, "Secret Agent Double-Oh-Frog", Kermit has second thoughts about donating his first banjo to someone who needs it more than he does, so he tries to get it back from Miss Nanny without her noticing. An Imagine Spot takes place where Kermit takes on the persona of Secret Agent Double-Oh-Frog and tries to get his banjo back from Fozzie and Gonzo as Oddfozz and Dr. Nose, who are on their way to deliver it to the city of Playroomopolis. At one point, they're all on a train, and Secret Agent Double-Oh-Frog wears a false mustache to avoid being recognized by Oddfozz and Dr. Nose. To get to Playroomopolis faster, Dr. Nose uncouples the coaches from the train, leaving Secret Agent Double-Oh-Frog on the uncoupled coach and needing to use Piggy as Agent Fabulous' bow-copter to catch up to them.
- Ninjago: In "The Rise of the Great Devourer", Pythor is on the Serpentine train headed to the city of Ouroboros to unleash the legendary snake creature known as the Great Devourer. After the ninja and Sensei Wu make their way to the front of the train, Wu separates the leading car from the rest so he can face Pythor alone in hope of stopping him, forcing the ninja the stay behind as Wu and Pythor continue toward Ouroboros.
- The Perils of Penelope Pitstop: In "Big Top Trap", while Penelope sleeps aboard the circus train, the Bully Brothers detach her car from the rest of the train so the Hooded Claw can set it on top of a skyscraper.
- Pippi Longstocking: In the season two episode "Pippi Takes a Train Ride", when the Crime Bros. get to the extra car on the train, one of them unhooks the car so they can't be followed by anyone else on the train. Pippi, Tommy, and Annika then unhook the two coaches to pursue them.
- Happens at the climax of The Simpsons episode "In Marge We Trust"; Flanders is trapped in a baboon enclosure at the zoo, so Lovejoy rescues him using the zoo's sightseeing train. When a baboon gets onto one of the cars, Lovejoy uncouples it.
- Thomas & Friends: The Troublesome Trucks will often break away from the engine that is pulling them, usually when that engine reaches the top of a hill. A few notable examples include:
Baz: Oh, dear. He's gone off on his own. One less to share with.
- "Troublesome Trucks/Foolish Freight Cars": When James gets halfway up Gordon's Hill, the Troublesome Trucks in the second half of his train break away. The conductor manages to stop the train and warn approaching engines until James goes back to re-couple the missing trucks.
- "A Close Shave/A Close Shave For Duck": The Troublesome Trucks break away from Edward after Duck helps Edward to the top of Gordon's Hill. They chase after Duck, who does his best to slow them to a halt. Though they just barely manage not to crash into James' passenger train, the trucks continue to push Duck, causing him to crash into a barber shop.
- "Busy Going Backwards": When Toad the Brake Van wishes he could go forwards instead of backwards, the Troublesome Trucks grant his wish by breaking away from Oliver when he reaches the top of Gordon's Hill. With no conductor to slow Toad down (due to having jumped clear), the signalmen take action by switching the points to avoid having Toad crash into other engines. Toad eventually comes to a stop in a muddy pond.
- Cows/A Cow on the Line: A train Edward is pulling gets uncoupled when a group of cows, disturbed by the noise he's making, break the fence separating them from the railroad tracks and run across the line. In the process, the last freight cars and brake van on Edward's train get uncoupled.
- "Duncan Gets Spooked": Early in the episode, Peter Sam stops at a water tower to refill his tank, when the Troublesome Trucks break away from him. They pass a sign that says, "Slow Steep Bends and Ravine Ahead", and fall off the Old Iron Bridge, landing in the swamp below.
- "Duck and the Slip Coaches": Duck tells the engines the story of how he used to pull Slip Coaches, special coaches that could be uncoupled at any time so that the passengers inside them can stop a specific station and the engine pulling them doesn't have to stop. When Sir Topham Hatt needs an idea on how to get the passengers to their destinations on time, James gives him the idea, but credits himself for it. However, since Duck is the only engine who knows how to properly use Slip Coaches, James ends up needing Duck's help in the end. Duck's Slip Coaches re-appear in a later episode, "Last Train For Christmas", where they are used to help Connor get all his passengers home in time for Christmas.
- "Hasty Hannah", the titular Hannah gets pulled by James after Toby leaves her on a siding. Thanks to James, Hannah is now able to go as fast as she wants, but because she didn't listen to Toby's warnings that tramway coaches like her are not built for high speeds, she begins to break apart as James goes faster. Eventually, her coupling breaks and as a result, she is diverted onto a siding as James leaves without her.
- In the "Marvelous Machinery" special, Baz and Bernie steal Ruth's plans for her flying car and attempt to escape from Sodor on Kenji. When Kenji begins to slow down, Baz tells Bernie to climb onto Kenji's coach and uncouple it. Bernie does so, and Baz abandons him as a result. Kenji's stray coach also manages to stop Thomas, who tries to catch up to Kenji with Professor Freidrich's booster rocket.
- Wallace & Gromit: Spoofed in The Wrong Trousers, with Feathers McGraw separating the engine of a toy train to get away from Gromit. Gromit quickly improvises a new track to catch up.
- Batman: The Animated Series: When the Joker blows up a railroad bridge in "Christmas with the Joker", the Batmobile pulls up alongside the train. Batman rescues the conductor from the engine while Robin detaches the passenger cars and puts on the brakes.
- This used to be Truth in Television in 19th century British railways: instead of the train stopping at every station, the car for that station would be detached and allowed to coast to the station so as not to slow the train down. As trains became faster, the practice died out due to the increasing danger of uncoupling a car at high speed (as well as the need for one guard per car and keeping passengers in the right car at all times).