Sam Marks climbs into the front car of Apocalypse, a 55-mile-an-hour roller coaster about to debut at Six Flags America in Largo. It’s a day before the turnstiles will open to the public on Thursday, and the Swiss-built cars are spotless, brimming with that new-coaster smell.

“They’re still painting down there,” Marks marvels as he pulls the molded harness over his tie-dyed T-shirt. Below, workers in yellow safety vests put the finishing touches on a crashed Cessna, a burned truck and other mocked-up doomsday grace notes.

A thunderous bass line of dread rattles the loading station, where a crew member checks Marks’s harness. Apocalypse is a standing ride. And Marks stands alone, the only rider on the 28-passenger train.

“I am freakin’ about this music,” Marks says, loudly. “Hey Randy, what is this great music?”

Randall Wilke, the theme park’s director of operations, shrugs his shoulders.

“I dunno,” he says. “Apocalypse music.”

Marks nods. Wilke shoots a thumbs up to the board operator, and the lone passenger rolls into the end of the world.

Six Flags is offering this preview ride because the park is trying to shake off a years-long slump with Apocalypse, its first new roller coaster in more than a decade. It wants the blessing of Marks, one of one of the area’s most noted roller coaster fanatics.

For more than three decades, Marks has led a life of the loop. He runs Coaster Zombies, an Alexandria-based club of more than 200 hard-core coaster devotees who travel the world in the thrall of thrill.

By day an unmarried mailroom supervisor at Sibley Hospital, in his off hours Marks is the master of Texas Tornados, Skull Mountains and Nitros, the fearless rider of Boomerangs, Screamin’ Eagles and Zydeco Screams.

“We live to ride, that’s the motto of the Coaster Zombies,” says Marks, who has already made his annual purchase of more than $600 worth of season passes to Six Flags, Kings Dominion, Busch Gardens Williamsburg and several other nearby theme parks.

At 54, Marks has logged hundreds of twirling hours along thousands of twisting miles, amassing a life list of more than 9,000 turns on 760 coasters.

Here at his “home park,” he reckons he has ridden the Wild One, Six Flags’ classic wooden colossus, more than 1,000 times.

“I’ve ridden it for three hours straight,” says Marks, who is especially partial to the big timber coasters. “And that’s not even a record. Some people are complete nuts. I’m borderline.”

‘I love the fire’

On this day, Marks gets four rides on Apocalypse. On the third, after some Six Flags interns and a reporter have climbed aboard, he describes what he looks for as the car clank-clank-clanks up the first hill: “floater” airtime, “ejector” airtime, some good lateral throws.

Marks rides a new coaster the way a wine connoisseur sips a new vintage, though he doesn’t swirl the glass so much as get swirled by it. But he savors the subtleties. Although “subtle” might not be the right word for a machine that hurls you at three Gs along a track shaped like a tangled shoelace.

“I love the fire,” he shouts after a plume of stage-managed flame erupts around the car. “That’s the kind of theme-ing that turns it from a ride into an experience.”

This will be Mark’s 761st coaster. Or will it? He knows that some purists will challenge his count because the coaster isn’t exactly new. Apocalypse is actually the repurposed Iron Wolf from Six Flags Great America in Illinois. The 2,900 feet of curlicue steel was trucked in and re-themed with a giant skull and end-of-time trappings.

“Someone will say: ‘Really? Didn’t you ride it in Chicago?’ ” Marks says. “That happens every time they transfer a coaster to a new park. But I say it’s a completely new experience.”

Coaster people are like birders, lighthouse buffs and train spotters. They share two loves: coasters and arguing about coasters.

“There are no rules, so we argue about everything,” Marks says. “Mostly it’s about fellowship, but some people get pretty fierce. One guy started de-friending everybody on Facebook.”

Thrill seekers unite

Coaster Zombies is one of at least three Washington area coaster clubs, and most of those thrill junkies also belong to the 5,000-member American Coaster Enthusiasts, the country’s biggest group. The clubs organize conventions, produce podcasts and converge on theme parks for special all-you-can ride events open only to members (the one at Kings Dominion each year is known as Hurlfest).

But mostly they band together for coaster pilgrimages, multi-park junkets that last a weekend or a week. Marks spends hours sweet-talking theme park managers from Canada to Mexico to get special access for his riders, often in the hours before opening or after closing.

Some groups specialize in European parks. The Zombies plan a visit to some promising coasters in Guatemala.

“I really don’t know if some of the people have jobs — you see them everywhere,” says Marks, who stays in cheap motels and lives on theme park hot dogs to stretch his coaster budget.

The parks have a mixed relationship with the coaster-heads. They welcome their intense devotion, their word-of-mouth networking and their unparalleled expertise.

“When a coaster enthusiast says, ‘This is just right,’ that is a great compliment,” says Six Flags America Director of Marketing Linda Jensen.

On the other hand, coaster nuts can — and often do — thwart parks’ plans to keep their big new rides under wraps until the big reveal.

“Yeah, some of us go to great lengths to know what’s going on,” Marks says.

He monitors Prince George’s County Web sites to see if any building permits or zoning hearings involve the Six Flags address on Central Avenue. And he once signed up for a free introductory flying lesson at a nearby airfield, then asked the instructor to fly him over the theme park.

After they landed, he said he’d changed his mind about the lessons, thanks, and hurried home to post the results of his recon mission: stacks of red and blue steel that were soon to become the Superman coaster, now visible beyond the loop of Apocalypse.

Coasters vs. the Beltway

“Awesome ride,” Marks calls out Wednesday as the car glides back along the platform. “It jolts you a bit, but who said the end of the world was going to be a cake walk?”

Marks says he’s encouraged to see signs of life at the park where he and some of his buddies went from coaster fans to Coaster Zombies back in the early 1990s.

After a 2009 bankruptcy, the directors who took over from a board led by Washington Redskins owner Daniel Snyder plan to make up for the lack of investment and the reputation for surly service that have dogged the place in recent years.

“Not only is that gentleman no longer here,” Jensen says, speaking of Snyder, “but whatever hangover there might have been from that culture is gone.”

But for Marks, it’s all about the coasters. He traces his love for them to his grandmother’s iffy driving. There was a certain dip in the road that Granny would hit on her way to the grocery store, and Marks loved the stomach-dropping sensation of it. When he was 12 and rode his first coaster, the Mine Train at Cedar Point in Ohio, he was hooked.

“It was the same cool feeling, except my head didn’t hit the ceiling,” he says. “It’s the out-of-control feeling, it’s the speed, and it’s the safety. I know roller coasters are safe, so I can enjoy the sensations.”

He sees driving to the theme parks as the riskiest part of his hobby. Three Gs on a string of inverted loops? Bring it. Seventy miles an hour on the Outer Loop? No, thanks.

“I may go five miles over the speed limit on the Beltway, but that’s it,” Marks says. “Driving is way too dangerous.”