If you’ve ever witnessed innocent digital thrill seekers thrown off a poorly-conceived ride on RollerCoaster Tycoon, you’ll know that the design of thrill rides is best left to the professionals. Brendan Walker is one such professional, and at New Scientist Live this weekend, he revealed some of the physics, mathematics, psychology and biology you need to have a grip on to ensure people are left scared, but not scarred.
Let’s take the loop-the-loop, for example. The first instance of this, from 1901 in Coney Island, was just that: a single loop-the-loop. And it worked well… if you didn’t mind a chance of whiplash and head trauma. That’s always a risk if you face 10Gs of force in an instant.
Over a century on, and Walker can speak fluently about what you need to achieve this feat not just with vehicles, but with people on a slide – as a TV crew once asked him to try. “Firstly we need potential energy - height at the top of the slide,” he explains. “As we go down the slide, that's converted into kinetic energy which gives us velocity and the speed we need. As we go into the loop we need centripetal force, which sticks you to corners. The centripetal force still needs to be large enough when you get to the top that the effects of gravity don't overweigh it and you drop out.”
The problem with that? You can’t throw people down a slide at 10Gs for obvious safety reasons. Ride designers get around this with something called the clothoid loop: two circles of different diameter. You hit a looser loop first with a low centripetal force, minimising g-force levels and, as velocity drops, you can safely go into a second tighter loop. That’s why you no longer have nurses station at the end of rides to treat for head trauma. Despite the warning precedents, Walker managed a single-loop vehicle-free loop-the-loop, but it never made it onto our screens as it was still viewed as too dangerous. Here it is in GIF form from another talk:
But there’s more to making an engaging thrill ride than just physics and avoiding injury, and much of it is down to psychology. Working off questionnaires, interviews and biological responses including neurological monitoring, heart-rate variability, skin sweat and pupil dilation, Walker has his own equation for this which squares arousal against pleasure:
“Our levels of arousal track quite closely the changing forces on a roller coaster, but that is only half the picture because thrill also relies on the element of pleasure which is a far more subjective part of human experience, and that's where the artistry comes into it,” Walker explains to me on the phone a few weeks before his talk.
The main thing, you see, is that optimal thrill factor comes from the contrasts inherent in ride design: you need the lows to appreciate the highs, in other words. “We experience thrill when there's a rapid and large increase of pleasure and arousal together,” he explains. “You get this rush of dopamine and adrenaline - that's starting from a base point. If you can pull them lower and make them feel fearful, create displeasure, then not only will the release from this displeasure cause thrill, but if you can give them something that's exciting, fun and cathartic and will make them laugh afterwards, then the move in that thrilling trajectory is even greater.”
To that end, there’s a theoretical maximum that the thrill level a roller coaster can physically achieve. Against this scale theme park rides routinely achieve a score of around 20% on the Walker Thrill-Factor scale, something that theme park management often find disappointing. Walker thinks they’re beating themselves up over nothing: “When you think of thermal efficiency of combustion engines, they're around 20% too. So I think theme parks aren't doing too badly turning potential energy into emotional energy.”
Interestingly, much of the psychology kicks in long before you actually sit down in the chair. “Part of the success of any ride relies on marketing. The story that is told which can go on for days and weeks in advance from buying the ticket to strapping in,” Walker explains.
“You've probably got more chance of dying from falling off a donkey at Blackpool beach than you have of falling off a roller coaster, but people perceive it to be dangerous and that's part of the marketing.”
But the very peak of thrill, according to Walker’s own research, actually comes before the ride kicks in. “The moment the restraint bar is pulled down and locked in – that's the peak moment in arousal. After that, you only achieve 80% of that.
“There's something about the fear of the unknown and what might happen to you, compared to the actual reality of what does happen to you. That's the moment that really intrigues me – when you're locked in and there's no escape.”
A thrill without spills?
This is why the restraint bar is authentically replicated in Walker’s pet project: a VR roller coaster, designed and built by a team of engineers from the University of Middlesex. A chair on a moving platform is supported by air muscles that flex and contract in time to what’s happening on the VR headset, but as graduate assistant Denis Tsvetkov tells me after I’ve tried the thing, the bar is purely a nod to realism: “It's completely not a safety thing - the platform only tilts around 20 degrees, so there's no real danger of you falling out.”
That’s not how it feels at the time, as I am briefly taken away from hubbub of the show floor to an authentic steel roller coaster. The only thing missing is the wind in the face. “We've been consistently been getting that as feedback,” Tsvetkov tells me when I bring this up. “The handlebars come from the top, so we're considering building something that can attach to that.”
You may feel this virtual experience isn’t really in the spirit of roller coasters, but it’s not without precedent. In his talk, Walker points to a 19th century ride called “The Haunted Swing.” Guests would enter a room and sit in a giant baby’s pram that would rock back and forth, getting faster and faster until they were actually upside down. They weren’t, of course: unbeknown to them, the room was also on an axis swinging in the opposite direction creating a powerful optical illusion. Appropriately, this ride attracted the same kind of scientific wonderment that Walker spreads now, getting this write up in the 1895 periodical Psychological Review: "The curious and interesting feature however, was, that even though the action was fully understood, as it was in my case, it was impossible to quench the sensations of 'goneness within'."
The text implies that many late 19th century American gentleman subsequently lost their lunches, but in the 123 years since The Haunted Swing debuted the world has come a long way, and VR tricks the brain without literally needing the room to spin. The drawback – and it’s a pretty major one – is the cost: the VR roller coaster chair will cost you between £8,000 and £10,000 to build. And you can if you want: the guides are all open-source, in order to encourage schools and universities to work on their own.
Despite this, Walker believes that this kind of VR experience is the future of thrill. “I'm not just interested in VR because I think it can be bolted onto roller coasters, but because it can be distributed globally,” he explains. “The concept of a theme park doesn't need to be geographically located, it can be an idea, and experiences can be created and distributed in very different ways,” he adds imagining a world where a fantastical VR scene can be projected onto skydivers or bungee jumpers. He already has a VR experience that can augment the standard playground swing to make you feel as if you’re a jellyfish under the sea, or speeding through a cityscape. He doesn’t anticipate buy-in from the big theme parks though – not at first anyway. “They won't make the giant strides that are necessary at this stage."
The here and now
Still, they have his number: he’s designed and consulted on thrill-ride design for years, and actually has a story of saving Alton Towers thousands of pounds. The ride is Thirteen, and if you’re not familiar – SPOILERS – the ‘coaster doesn’t end when it seems to. Instead, the floor gives way and you fall into a pitch black room, and proceed to accelerate backwards. “They asked me how far they needed to drop members of the public for them to be thrilled,” Walker explains. “Every foot of steelwork was going to cost them tens of thousands of pounds to produce so they needed to get it right, but they wouldn't let me build a test track.”
How do you get around that problem? As ever with Walker, the answer is by turning to science: he looked at studies examining the average human response time to unexpected stimulus. “The rule I set myself: as soon as the hands grip the side of the ride, your brain has had time to process the information and create a response... something like 500ms for the 95th percentile." That meant 1.2 seconds of freefall, or around 2.4 metres to recognise the danger, and seven metres to respond to it. In the end, he managed a workaround that only required five: there’s an initial 30cm jolt that doesn’t actually go anywhere, before the five metre drop kicks in – a cunning psychological trick to save thousands of pounds worth of steel.
Thorpe Park’s Saw. Image: Wikipedia
But perhaps Walker’s main strength is not as a designer, but as a critic. So which rides thrill the man himself? “It's not exhaustive,” he laughs. “I keep thinking I should create a Michelin Guide to all the rides.” Ultimately, he names two: the first is the Saw ride at Thorpe Park. “It may not have provided the peak highest thrilling experience - like the singular moment at Oblivion at Alton Towers – but what it did do over the graduation of three minutes was, like a well choreographed piece of music, it kept delivering a new thrilling experience,” he explains. And if you can’t get to Thorpe Park, you’ll find a family-friendly identikit version called Rage sat at Southend’s Adventure Island. Something Walker discovered when he couldn’t get the adult themes of the Saw ride onto a segment of Blue Peter.
The second is a bit of a wildcard: Spinball Whizzer at Alton Towers. “It's a coaster that doesn't invert, and because the car spins, you don't know which way you'll be facing,” Walker explains. “And because you're always looking at other riders, it doesn't fails to make people howl with laughter. It really bucks the trend when people think about what makes a successful thrill ride.”
Whether it’s screams or laughter, then, social bonding remains a key part of the thrill-ride experience. Walker’s vision for a VR-based thrill-seeking future may have the basic mechanics right, but until the medium becomes a truly social experience, family days out to Alton Towers should have a good few years left to dish out the screams.