After more than a century of striving to propel screaming riders ever faster, higher, steeper and longer, many roller coasters now hurtle to the limits of human endurance. So where is there left for the tracks to go?
The new attraction at Thorpe Park in Surrey, Saw - The Ride, claims to offer the world's steepest freefall drop - a beyond-vertical 100-degree descent back under the ride's 100ft (30m) peak.
It takes about three seconds.
 Fasten your seatbelts |
An even steeper 112-degree descent is due to be unveiled in July on a new ride - Mumbo Jumbo - at Flamingo Land in North Yorkshire.
Roller coaster one-upmanship is something of a tradition in the amusement park industry, with rides sometimes designed seemingly with headlines as much in mind as effective frights and thrills.
Coasters now stand hundreds of feet tall, race at speeds nearing 130mph, and turn the rider upside down with multiple inversions. Predictably, the US boasts most of the world's roller coaster records.
"In America there are so many parks, there are always these coaster wars going on," says Andy Hine, founder and chairman of the Roller Coaster Club of Great Britain (RCCGB).
But he adds: "When you get into these coaster wars, you don't always end up with a good ride."
"A roller coaster represents a really well choreographed sequence of unusual stimuli," says Brendan Walker, director of Thrill Laboratory and a visiting senior research fellow at the University of Nottingham.
The farther a roller coaster can push its dual extremes of fear and pleasure, the more thrilling the ride will be, he argues.
"Thrill as an experience is actually defined as a large, rapid increase in pleasure and arousal together," he says.
"If you can manage to pull somebody towards displeasure through fear, through danger, and then provide a pleasurable release, the margin of change is larger."
Shake, rattle
Most roller coaster fanatics prefer wooden rides, despite them tending to be smaller and slower than steel ones, partly because of the more anxious experience often involved.
 | ANDY HINE'S COASTER TIPS Sit at the back of the train to whip over hills and enjoy more 'airtime' Extend your arms to stretch trunk and enhance physical sensations "Keep your eyes open no matter how scared", because the imagination only creates worse Trains go fastest just after rain and at the end of the day For shorter queues, start visit at the back of the amusement park, move round it anti-clockwise, and ride during lunchtime |
The swaying and creaking frame, the deafening rattle of the wheels on the track, and the archaic appearance can suggest that the ride - and consequently the riders too - may not be around that long.
"A wooden roller coaster has a lot more shake, rattle and roll about it," Mr Hine says.
With an estimated 35,000 rides on more than 2,000 of the world's roller coasters behind him, Mr Hine's favourite attraction is the wooden Phoenix, in Pennsylvania, US, standing at an unimposing 78ft (24m) and with a top speed of about 45mph.
Mr Hine claims that the most popular sensation offered by roller coasters is the weightlessness over a hill, when negative G-forces lift a rider out of their seat, and that this is more frequently experienced on wooden rides.
"They don't build them high, they don't build them fast. They have to compete in another way - they go for the fun factor," he says.
"They give you more 'airtime', which is an enthusiast's favourite part of the ride."
Not for no reason, Airtime is the name of the RCCGB magazine.
Adult fun
On their arrival around the turn of the 19th century, roller coasters held iconic status in a rapidly changing world, argues architectural historian Dr Josie Kane.
"Suddenly you get amusement parks that are permanent. People go by train or by car. They travel quite long distances to these sites. They are technologically interesting in a way fairgrounds weren't," she says.
"Roller coasters seemed to symbolise this massive, dramatic, radical change that people understood was happening with mechanised travel, industrialisation and technological advancement. They seemed to encapsulate that.
"They still do," she adds. "When people talk about the roller coaster of modern life, it's a metaphor for the fast pace, ups and downs and unexpected turns of living in a modern world."
A release from that metaphorical roller coaster is, of course, a fundamental part of the appeal of the real thing.
Height restrictions exclude most pre-teens from extreme coasters like Saw - The Ride, and attractions will insist children are accompanied by adults or offer warnings like: "Caution: May be a bit scary for the very young."
Mr Walker calls amusement parks "playgrounds for adults", where it is "socially acceptable to go and lose your inhibitions, and become as engaged as you want to, and scream".
"It's a bit of escapism," says Mr Hine. "When you go to a theme park you can leave all your worries at the front gate."
Downsize?
Saw - The Ride is a tie-in with the brutal horror films of the same name; from the moment people join the queue for the ride, grisly props of severed body parts and alarming sound effects aim to build tension and fear.
 The bigger they are... |
This combination of psychological and physical elements could hint at roller coasters' future.
"You can only go upside down so many times, you can only go 100mph so many times before it becomes boring," says Mr Hine.
"I think the days of really big rides are coming to an end."
Mr Walker expects theatrical elements to become increasingly significant in roller coaster design.
"We are on the borders of what the body can sustain," he says.
"Engineering could now do more to the body, but the body is a limiting factor. But the mind is as deep and as broad as you want to play with."
Having bounced the body around until it can take no more, roller coasters may start messing with the mind.
The next generation of rides could be mental.
The mind is as deep and as broad as you want to play with 
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