Roller coaster technology: 'Bigger! Faster! Scarier!'
Technology has transformed the theme park thrill ride, fuelling a global arms race to create the fastest, tallest, scariest roller coasters the world has ever known.
Alton Towers in Staffordshire has just opened the world's first 14-loop roller coaster, called The Smiler, while in Abu Dhabi, Ferrari World claims to have the world's fastest coaster.
But are we reaching the limits of what the human body - and theme park budgets - can stand? What will the thrill ride of the future look like?
Ferrari World's Formula Rossa ride blasts passengers from 0-149mph (240km/h) in just 4.9 seconds, with riders experiencing 4.8G during acceleration - G-forces only fighter pilots usually feel.
Its huge 25-tonne hydraulic winch and compressed nitrogen gas system produces 21,000 horsepower, 20 times that of a Formula 1 racing car.
John Wardley, designer of the Nemesis, Oblivion and Air rides at Alton Towers, said: "While we can withstand 6-8Gs for very short periods of time, if we experience 5G for more than five seconds, say, we're likely to black out.
"We can't push people any further than they can go at the moment."
On modern rides passengers experience about 3G in tight turns and loops, and zero G - the feeling of weightlessness - when upside down or flying over parabolic "bunny hills" and "camel backs".
"We reached the limit of G-forces a while ago, but there is no technological limit to how fast or how high roller coasters can go - it's all down to money," said Justin Garvanovic, founder of the European Coaster Club.
So what are the technologies that have enabled this move towards extreme rides?
The big breakthrough was the linear synchronous motor (LSM), capable of launching passengers from 0-70mph in about two seconds.
It is the same technology being developed by the US navy to propel jets from aircraft carriers as a replacement for the traditional steam piston catapult.
LSMs employ a series of electromagnets fired in sequence, with power being supplied from the latest generation of highly-efficient batteries.
They combine the launch, drive wheels and brake mechanisms all in one, allowing for blistering acceleration and equally effective braking by reversing the polarity of the electromagnets.
Crucially, this allows designers to reverse the direction of the ride, doubling the thrills without doubling the length of track.
The other major breakthrough has been 3D design engineering software from the likes of Autodesk, CATIA and Solidworks.
"Our software allows designers to create highly accurate digital prototypes and understand how a ride will behave before they build it," Carl Bass, Autodesk chief executive, told the BBC.
"It can predict the weakest point in the design; the likely fatigue rate of the materials; the speeds and G-forces."
This software, together with tubular steel tracks, innovative car and harness designs, and LSMs, have given designers the freedom to incorporate multiple launches and all sorts of vertical rolls, loops and corkscrews traditional coasters could never have managed.
For example, Projekt Helix, a 2014 coaster being developed by Mack Rides for the Liseberg amusement park in Sweden, will include two launches - Europe's first multi-launch coaster - accelerating riders to 62mph at 4.2G.
The two-minute ride will include a "pretzel loop", a twisted air-time hump, s-curves and a zero-G roll.
But insiders believe the thrill ride arms race is coming to an end because the costs are spiralling out of control.
Rides can cost from £2.5m to £25m, depending on their size and sophistication, with the likes of Disney spending even more on themed rides involving elaborate sets and animatronics.
Alton Towers' The Smiler cost £18m to build, while Projekt Helix will cost 23m euros (£19.5m).
"People were spending stupid money and had to take a step back," said Mr Garvanovic.
Steve Boney, spokesman for Maurer Soehne, a German thrill ride manufacturer, said: "There is a law of diminishing returns. As the magnets get bigger, they get heavier and much more expensive, and this pushes up the construction costs. Achieving an extra 50km/h [31mph] costs an extra three to four million euros [£2.5m-£3.5m].
"And greater speeds mean you have to increase the allowed rider heights, so fewer kids can go on the ride, reducing revenue," he added.
As a result there is move towards dark - or indoor - rides where the experience of whizzing round a track is enhanced by audiovisual technologies, like much larger versions of current simulator rides.
"The ride of the future will be an entertainment machine, as much about surprise, fun and enchantment as physical thrills," said Mr Wardley.
Mr Boney agrees, saying: "Audiovisual technology is where most of the technological innovation is happening."
For example, Dynamic Structures, the Canadian company behind the Harry Potter theme rides for Universal Studios, is currently developing a "coal mine-themed" ride for a client in Dubai that will incorporate thrill ride speeds and G-forces with 3D projection effects and robotics.
"It will be the most technically advanced ride in the world," Craig Breckenridge, senior designer at Dynamic Structures told the BBC.
"We're doing things with coasters that have never been done before, such as switching tracks, and using video and projections that will trick your brain into thinking you're really falling."
At certain sections of the ride the cars will drop vertically, laterally, and backwards on a tilting piece of track that takes them underneath where they've just been, said Mr Breckenridge.
So as the traditional thrill ride arms race comes to an end, it seems a new era of intense, multi-sensory, immersive dark rides is only just beginning.