Why Roller Coasters Click


Whether you’re a fan of riding roller coasters,
or you have simply played way too much Roller Coaster Tycoon, you are probably familiar
with the clacking, clicking, or clanking sound that many roller coasters make as they climb
the lift hill. What you may or may not know is that this
sound is part of a critical safety system that is designed to keep passengers safe as
they are lifted to the top of the ride. The system is known as anti-rollback, or ARB
for short, and it is used to prevent trains from rolling backwards in situations where
motion in the reverse direction would either be undesirable or dangerous. Most conventional roller coasters have stations
and tight unbanked turns located at the base of their lift hills, and these are not usually
designed to handle trains moving at high speeds. It would be quite disastrous if a train were
to fall backwards down the lift in this scenario, which is why carefully engineered anti-rollback
systems are used to ensure that this never happens. Unfortunately, this wasn’t always the case
in the early days of the roller coaster, and a number of catastrophic rollbacks have occurred
throughout history. The most notable accident occurred on the
Big Dipper at London’s Battersea Park in 1972, where the lift rope snapped and the
rollback brake failed, sending the train speeding back down the lift. 5 children were killed, and 13 others were
injured, when the train derailed on a curved section of track at the bottom of the hill. Ride failures like this one were extremely
tragic, but they have also led to a much higher standard of safety for the modern roller coasters
that we ride today. The ASTM F24 Committee was established in
1978, just 6 years after the Big Dipper accident, and they have developed a set of standardized
guidelines for the safe design and operation of amusement rides. These guidelines are revised and updated annually
by a team of more than 800 members, and they are referenced by ride manufacturers and operators
all over the world. ASTM Standard F2291 relates specifically to
the design of amusement rides, and it includes a number of requirements for anti-rollback
systems on roller coasters and other ride types. For example, it states that when anti-rollback
is required, no less than 2 independent devices must be provided for redundancy, and at least
one of these must be engaged at all times. This greatly reduces the risk of an accident
because two safety devices would have to fail simultaneously in order to cause a rollback,
and the probability of that happening is very low. Let’s say we have ARB device A with a probability
of failure of 1 in 50,000, and ARB device B with a probability of failure of 1 in 200,000. If both devices need to fail at the same time
in order to cause a rollback, then the associated probability can be calculated by taking the
product of the individual failure probabilities, which is 1 in 10 billion. The risk of an overall system failure is far
lower with 2 independent safety devices rather than just 1, and getting a rollback with a
redundant ARB system is virtually impossible. Now before we take a look at how anti-rollback
actually works, it’s worth mentioning that not all roller coasters require these systems. Vekoma boomerangs, for example, start by lifting
riders up a reverse incline before releasing them back down the same hill. It would not make sense to use ARB in this
case since the train needs to travel in both directions, and a premature failure of the
lift system would not result in any damage or injuries. Launched coasters don’t typically use ARB
either, as they are specially designed to handle rollbacks, and are often equipped with
fail-safe braking systems to bring the trains to a stop. Where you will find anti-rollback being used
is on roller coasters with conventional lift hills, where the trains are meant to travel
in the forward direction only. These rides typically use a chain or a cable
to pull the trains up the hill, and the lift mechanism itself is often the first line of
defense against a rollback. If the lift is brought to a stop for any reason,
then the drive system will engage a holding brake to prevent the chain or cable from slipping
backwards, which will keep the train stationary on the hill until the ride is started back
up again. If the holding brake were to fail, or if the
chain or cable were to snap unexpectedly, then there is a secondary anti-rollback device
that would act as a fail-safe. For chain and cable lifts, the secondary ARB
usually consists of a ratcheting system, which produces that classic clicking sound we are
all familiar with. The way it works is basically the same as
a handheld ratchet… except on a much larger scale. There’s a steel rail called a rack that
is mounted on top of the lift track, and it has asymmetric teeth that are sloped up towards
the top of the lift. Metal pawls hang down below the train which
slide over the teeth as the train is pulled up the hill, and they are pinned at one end
so they fall into the grooves under their own weight. These pawls are commonly referred to as anti-rollback
dogs, since they are designed to catch against the rack when the train moves backwards. The shape of the teeth allows them to easily
slide over the rack in the forward direction, but they will lock into the grooves in the
reverse direction to prevent the train from rolling back down the hill. This mechanism is extremely reliable because
it operates entirely under gravity, and it will always be engaged whenever a train is
present. As you head up the lift hill on a roller coaster,
you can usually see the rack running parallel to the chain or cable, and the clicking sound
that you hear is the pawls falling into the grooves between the teeth. Many parks prefer to minimize the noise as
much as possible, though, and soft pads are often installed on the pawls to dampen the
sound. On rides that have heavier trains and steeper
lift hills, like B&M dive coasters for instance, you will typically see 2 racks installed on
the track instead of just 1 in order to handle the additional load. Each car has its own set of pawls to distribute
the weight across multiple teeth, which also protects the individual cars from a rollback
in case they become separated from the rest of the train. ASTM F2291 specifies that every car must be
equipped with its own secondary anti-rollback device for this very reason, unless the cars
have a redundant safety mechanism such as a cable or chain holding them together. In this photo of the Griffon dive coaster
at Busch Gardens, you can see that each car has 4 pawls with polymer sound dampers that
align with 2 racks on the lift hill. The device suspended in the middle is the
chain dog, which connects the car to the lift chain. The slotted cutouts that you see in the pawls
and chain dog all have pins running through them, and this limits how far the dogs are
able to drop below the bottom of the car. B&M dive machines have some of the heaviest
trains out there, so this is pretty much the most robust anti-rollback system that you
will see on any roller coaster. For a quick comparison, the Leviathan giga
coaster that we saw earlier was built by the same manufacturer, and it only has 1 smaller
pawl on each car. For rides that have trains positioned below
the track, such as inverted or suspended roller coasters, the secondary anti-rollback device
needs to be slightly different because the ratcheting system cannot rely on gravity. Many of them still use the same mechanism
that we have already seen, however the rack is positioned upside down above the train
instead of below, and the pawls must be spring-loaded so that they are pushed up against the teeth. Some inverted coasters such as Vekoma SLCs
use a non-ratcheting system instead, but it works in a pretty similar same way. There’s a flat steel fin that is fixed to
the track which runs parallel to the lift chain, and two spring-loaded cams are mounted
to the top of each car. As a train is pulled up the lift, the fin
pushes the cams apart freely, but if the train begins to move in the reverse direction, then
they will wedge against the fin and prevent the train from rolling backwards. The cams have small teeth that bite into the
metal to increase the frictional resistance, and they will clamp together harder and harder
as more force is applied from the train. This type of mechanism is known as a unidirectional
bake, and it is used extensively as a fail-safe in the elevator industry. One of the benefits of a non-ratcheting ARB
like this one is that it produces less noise, however some roller coaster manufacturers
have also developed clever ways to make their ratcheting systems silent. Intamin, for example, utilizes the principle
of electromagnetic induction to hold the pawls above the rack when the train is being pulled
up the lift. There’s a small wheel that runs along a
separate rail on top the track, and this spins a circular conductive plate as the train rolls
forward. A lever with a permanent magnet is positioned
just behind the plate, and it is connected to the pawl, which is able to pivot up and
down. When the wheel spins clockwise, the magnet
induces an electric current in the plate which creates an opposing magnetic field. This produces a counter-clockwise torque on
the lever, which in turn lifts the pawl away from the rack. As long as the train continues moving forward
with enough speed, the pawls will remain disengaged and the anti-rollback system will be silent. However, if the train comes to a stop and
starts to roll backwards, then the torque from the electromagnet will reverse direction
and push the pawls down into the teeth. If the ride is running on a rainy day, then
it’s also possible for the pawls to engage while moving forward because the wheel may
slip when the track is wet. Sound dampers are rarely used on these electromagnetic
systems because their primary purpose is actually to reduce wear and tear rather than noise,
and so they tend to be extremely loud when this happens. Each type of anti-rollback device has its
own advantages and disadvantages, though, and they all achieve the same goal of making
roller coasters as safe as possible. Modern ARB systems are engineered to be completely
fail-safe, and the probability of failure for any of them is extraordinarily small. With standardized design rules like those
provided by ASTM F24, the roller coasters that we ride today are safer than they have
ever been in the past. With that being said, I still prefer the simpler
anti-rollback designs with fewer moving parts because there is even less that can go wrong,
and I’m also a big fan of that iconic clicking sound. Now, before I head off to play a game of Roller
Coaster Tycoon, I’d first like to thank NordVPN for sponsoring today’s video. While theme parks make it their top priority
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100 thoughts on “Why Roller Coasters Click

  1. I decided to make a few small changes to this video last night and ended up with countless rendering issues that I had to stay up all night to fix. It probably wasn’t worth it, but that’s what I get for trying to change things at the last minute 😅

    Anyway, I hope you all enjoy!

  2. -makes a video about the mechanics of clicking on rollercoasters chairlift
    -puts Skyrush in the thumbnail

    Great video, as always !

  3. You missed arrows solution on their suspended coasters where they found a way to use just gravity on its anti rollbacks. The anti rollback dogs are on the lift itself and the ratchet system is on the train.

  4. More on the probability for a rollback, not only do those safety system have to fail, the chain also has to malfunction; further lowering the chances of a rollback

  5. Thought I was going into this video with nothing left to learn. But you pleasently surprised me. Didnt know about the Intamin system or the SLC system.

  6. Don’t ask me what the engineers were thinking on Big Dipper. Using a normal rope that can wear out to lift a heavy train is a terrible idea

  7. This is just out of curiosity, but you did use alot of stuff from Canada's Wonderland so are you Canadian or do you just really like Canada's Wonderland?

  8. As a ride operator for millennium force thank you so much for explaining how the cable lift ARB works. Great explanation for the least known ARB system

  9. So, in the case of inverted coaters, why don’t they put the moving piece repeating on the top while the still parts are on the cars?

  10. As usual incredible work! You talked about all the technologies we use and cited 2291 😍 I will be using these videos to help educate engineering students going into this industry. As always if you want help researching a video I work with ASTM F24 and have worked with every ARB system in this video so feel free to reach out to me on linkedin. Keep it up!

  11. The whole "vpns keep you internet traffic safe" is complete bs. Watch this video from tom scott and you'll understand why: https://youtu.be/WVDQEoe6ZWY

  12. Rollback is not the cause of the clicking. It is a system that can possibly cause it, but there are other antiroll back systems. The only system that makes this noise that also functions as an antiroll system is the dog tooth lift system. Nice video overall though.

  13. Definitely the best video I have seen on this topic. I thought I knew most things in this topic, but you really cleared up some extra stuff, especially with those electromagnetic systems. I reckon most people underestimate the amount of engineering that goes into building Rollercoaster.

  14. Good video! I wish someone had a video of archive footage of Canada’s wonderland original roller coaster construction, like original minebuster track layout, ect.

  15. You don’t talk about Wodan Timburcoaster Chain failure at Europapark ? That could be a good intro ! But anyway you vids are howesome, and I improve my English skills in the same Time !
    Hi from France 🙂

  16. I work at crush"s coaster at disney land paris , on the maurer sohne spinning coaster , there is a system who raises the pawl when the vehicle go forward on the lift , and drop down when the vehicle go backwards

  17. Having worked as a tech on multiple coasters previously, I appreciate the level of accuracy your videos always have. As a fun fact, the first safety in the lift mechanism is called a sprag clutch, which prevents the sprocket holding the chain from rotating in the reverse direction when the sprags engage with the clutch's outer race (a circular version of the Vekoma SLC rollback mechanism). As long as the sprocket is held, the chain cannot reverse its direction, preventing the chain from rolling backwards.

  18. Would it be an issue if both arbs failed but the train was at the start like halfway bent upwards would it still be an issue then

  19. In 2017, a ride at Six Flags New England called The Great Chase put its brakes on to soon, and when the dispatcher tried letting us ride again, the train rolled backwards. It was also a kid roller coaster. But it didn’t get destroyed.

  20. I knew the second that coster sped in that it was el toro ive been to six flags way to much

  21. The big dipper is not in London or in Battersea park it is in balckpool in Blackpool plaeasyre beach

    Unless I’m mistaken and there was another one in history but the crash turn thing did look quite similar to the Blackpool coaster

  22. I have a serious question if I want to be a roller coaster designer would I have to master engineering in college? I’m pretty sure I do but if you know that you for reading this.

  23. I'm not going to watch this but as someone who knows the answer, 12 minutes is a disgusting length for this video.

  24. I never thought that it is a Problem when a Train move backwards. I thought all Tacks can handle the Train on High Speed O.o

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