Back in the early 20th century, engineers attempting to push the limits of roller coaster thrills subjected riders to risky upside-down turns and bloody noses. A century later, coaster designers rely on computer software, physics, and psychology to push the limits of the roughly 5000 rides in operation worldwide. To get a sense of what their job entails, Mental Floss spoke with several roller coaster specialists about everything from testing rides with water-filled dummies to how something as simple as paint can influence a coaster experience. Here’s what we learned.

1. Getting strapped in might be the most exciting part of the roller coaster ride.

Known as a “thrill engineer,” UK-based Brendan Walker consults with coaster manufacturers and parks on the psychology of riding the rails. In his experience, riders getting secured into their seats are at the peak of their excitement—even more so than during the ride itself. “The moment the lap bar is being locked down and you have that feeling of things being inescapable, that you have to suffer the effects of the ride, is the highest moment of arousal,” Walker says. “The actual ride might only achieve 80 percent of that excitement.”

2. Designers test roller coasters with water-filled dummies.

Bill Kitchen, founder of U.S. Thrill Rides, says it can take anywhere from two to five years for a coaster to go from idea to execution. Part of that process is devoted to the logistics of securing patents and permits for local site construction—the rest is extensive safety testing. “We’re subject to ASTM [American Society for Testing Materials] standards,” Kitchen says. “It covers every aspect of coasters. The rides are tested with what we call water dummies, or sometimes sandbags.”

The inanimate patrons allow designers to figure out how a coaster will react to the constant use and rider weight of a highly trafficked ride. The water dummies—which look a bit like crash test dummies, but filled with water—can be emptied or filled to simulate different weight capacities. Designers also sometimes use the kind of crash-test dummies found in the auto industry to observe any potential issues prior to actual humans climbing aboard.

3. Every foot of roller coaster track costs a lot of money.

Thrill seekers go upside-down while riding on the Mind Eraser roller coaster in Agawam, MassachusettsKirkikis/iStock via Getty Images

There is absolutely nothing random about the length of a coaster’s track. In addition to designing a ride based on the topography of a park site, designers take into account exactly how much space they’ll need to terrorize you and not an inch more. When England’s Alton Towers park was preparing to build a ride named TH13TEEN for a 2010 opening, they asked Walker exactly how much of a drop was needed to scare someone in the dark. “It was a practical question,” Walker says. “For every extra foot of steelwork, it would have cost them £30,000 [roughly $40,000].”

4. Rollercoaster Tycoon brought a lot of people into the business.

The popular PC game, first released in 1999, allowed users to methodically construct their own amusement parks, including the rides. As a proving ground for aspiring engineers and designers, it worked pretty well. Jeff Pike, President of Skyline Attractions, says he’s seen several people grow passionate about the industry as a direct result of the game. “I remember when the game first got popular, I would go to trade shows and there would be kids looking to get into it using screen shots of rides they designed. The game definitely brought a lot of people into the fold.”

5. Paint makes a big difference in coaster speed.

scanrail/iStock via Getty Images

For all of their high-tech design—the software, fabrication, and precise measures of energy—a good coaster ride can often come down to whether it’s got too much paint on it. “The one thing that will slow down a steel coaster is a build-up of paint on the track rails,” Pike says. “It softens where the wheel is rolling and hitting the track, which increases the drag.” A good, worn-in track will have gray or silver streaks where the wheel has worn down the paint, making it move more quickly.

6. A roller coaster’s skyline is key.

Brian Morrow, former Corporate Vice President for Theme Park Experience at SeaWorld Parks and Entertainment, says that the looming curvature of coasters spotted as guests drive toward and enter the park is very purposeful. “It’s like a movie trailer in that we want you to see some iconic coaster elements, but not the whole thing,” he says. “You approach it with anticipation.”

7. Some coasters arrive as giant model kits.

Whether a coaster’s theme or design comes first is largely left up to the end user—the amusement park. But for some rides, manufacturers are able to offer pre-fabricated constructions that designers can treat like the world’s biggest Erector Set. “Sometimes I work on rides that have already been built,” Walker says. “They’re produced by a company and presented almost like a kit with parts, like a model train set. There’s a curve here, a straight bit here, and you can pick your own layout depending on the lay of the land.”

8. Wooden roller coasters are weather-sensitive.

If you’ve ever been on a wooden coaster that seems a little shaky from one trip to the next, check the forecast: It might be because of the weather. Pike says that humidity and other factors can shrink the wood, affecting how bolts fit and leading to a slightly shakier experience. “The structure itself can flex back and forth,” he says. It’s still perfectly safe—it just takes more maintenance to make sure the wood and fasteners are in proper operating condition. A well-cared-for wooden coaster, Pike says, can usually outlast a steel model.

9. The time of day can affect the coaster experience.

“A coaster running in the morning could run slower when cooler,” Morrow says. “The wheels are not as warm, the bearings are warming up. That could be different by 2 p.m., with a slicked-up wheel chassis.” Coasters experiencing their first-ever test runs can also be slightly unpredictable, according to Pike. "Those first trial runs [during the testing phase] can be slow because everything is just so tight," he says. "A lot of coasters don't even make it around the track. It's not a failure. It's just super-slow."

10. Roller coaster designs can come from unusual places—like Jay Leno’s chin.

The twisting, undulating tracks of coasters can often be the result of necessity: Pike says that trees, underground piping, and available real estate all inform designers when it comes to placing a ride in a specific park. But when they have more freedom, coasters can sometimes take on the distinctive shape of whatever happens to be around the designers at the time of conception. “We had a giant piece of land in Holland that just had no constraints, and we were sitting around talking," Pike says. “And we started talking about Jay Leno’s chin.” The ride was a “loose” representation of the comedian's jaw, but “it is there.”

11. Roller coaster riders double as performers.

A woman taking a ride on a rollercoaster at Oktoberfest in Munich, Germanyexithamster/iStock via Getty Images

For Walker, the best advertising for a coaster is having spectators watch riders de-board after an exhilarating experience. “It’s all about that emotion,” he says. “A spectator basically asks, ‘What’s making them so aroused? What’s giving them such pleasure?’ The line for the ride is the audience. Imagining yourself on the structure becomes a very powerful thing."

12. The future of coasters is vertical.

Biggest, fastest, longest—coasters are running out of superlatives. Because rides can only be designed with so many drips, rolls, or G forces, some companies are looking to the sky for their next big idea. Kitchen has been overseeing design of the Polercoaster for years: It’s a sprawling, skyscraper-esque ride that uses electromagnetic propulsion to carry riders upwards instead of across horizontal tracks. “We want to put it in places where land is very expensive, like the Vegas strip,” he says. “You can only do that if it takes up a lot less space.” The project is set to exceed the 456 feet of the current tallest ride, Kingda Ka at Six Flags in New Jersey. “It’ll be the world’s tallest—and hopefully the most fun.”

This list first ran in 2017.