At Zion National Park, they don't seem at all eager to forget the bad old days. In fact, around the visitors center on a stunning June morning, it's easy to find folks happy to dish about how awful a summer visit to Zion used to be.

"Oh, it could be miserable," says Tom Haraden. He's a boyish, mustachioed ranger in the Ron Howard mode, and he talks about Zion's famous peak-season gridlock with something like glee: Each day, more than 5,000 cars, buses and RVs jammed the six-mile scenic road into the heart of the park, all vying for fewer than 500 parking spaces at the trailheads and scenic spots along the way. The result was a chronic bad-tempered backup. Tailpipe haze smothered the juniper air, horn honks and muffler roars overwhelmed the whisper of the nearby Virgin River, and purple oaths echoed from ocher cliffs. In all, a summer day in Zion -- with its biblical name meaning "place of sanctuary" -- boasted all the appeal of a Manhattan rush hour.

"It wasn't the number of people, it was the number of cars," says Haraden. "Some days, it was just a giant conveyor belt of cars, out to the end and back with no place to stop or park."

Ranger Rebekka Anderson remembers the bleak effect traffic had throughout the canyon, even from 3,000 feet above. "You could hear it from Angels Landing," she says, referring to one of the park's highest outlooks, a soaring rock peak with a falcon's-eye view of the terrain below. "After a hard hike up there, you'd look down and see nothing but bumper-to-bumper cars."

And now? "You should go up and see," Anderson says, beaming.

There's still a bright line of morning sun creeping down the red cliff face as I walk out to the curb, where a big white bus waits to take me on a tour through the future of America's national parks. Day is still just shouldering aside the cool canyon shadows, but the large parking lot behind the visitors center is more than half full of cars. A steady current of visitors flows through the wide plaza of the new $2.5 million center, eddying around the handsome timber kiosks where carefully crafted displays brief them on Zion's attractions and history. Two of the kiosks are devoted to describing various half- and full-day itineraries, and by the time they reach the covered timber bus shelter on the far side, most people should have a pretty good idea how Zion works.

Zion, in southwest Utah, is one of the Four Corner parks, and tourists typically add it to their circuit visits of Grand Canyon, Bryce Canyon and Arches national parks. Like those others, Zion is defined by the dramatic landforms carved by the eons from the high desert plateau, most notably the tight and winding Zion Canyon. Its intimate grandeur -- a soaring corridor lined with homey riverside clearings and a variety of day trails -- drew almost 2.7 million folks last year. That's where the shuttle goes.

At the white bus, emblazoned with a golden eagle on the side, I step aside for an older couple to make their way up the steps -- slow but serious hikers, judging by the matching Tilley hats, the Magellan GPS unit and their Komperdell collapsible trekking poles. I follow a family of four, fragrant of sunblock and each wearing a day pack. The bus is half full, and at the back, a group of college-age women make last-minute adjustments to the bulging overnight backpacks on their laps.

"Welcome to Zion National Park and the Zion shuttle," says the driver after we pull away with a hydraulic hiss. His spiel is carried on speakers in our bus and through the attached trailer bus trundling behind us. "The Zion shuttle is the only access into the canyon and the Zion Scenic Drive. We'll be making eight stops on our way up-canyon. You're welcome to get off at any stop, stay as long as you like and get back on another shuttle. Buses run every seven minutes. If you were to stay on the bus for the entire loop, the trip up and back will take about 90 minutes. The last shuttle to the visitors center departs the Temple of Sinawava at 11 p.m.

"First stop, the Zion Human History Museum."

At first, though, we're not going anywhere. The shuttle idles quietly for a good four minutes near the park entrance, as an unyielding string of cars and RVs zips by. Nothing surprising about that. Some 2,800 cars will pour into the park on this beautiful June day in southwestern Utah, bring some of the 2 million-plus visitors that come to Zion each year. This edge of the park is completely open to traffic.

Finally we pull out and join the pack heading along Route 9. But after about a mile, something profound happens. The traffic forks right, toward the Mount Carmel Tunnel, and points east. But the shuttle bears left, into the heart of Zion on a highway that is utterly empty. It's quiet, a two-lane drive all our own. The road is open and so are all the windows; a pinyon breeze ruffles hair and bandannas all along the bus.

"If you look to the left, you'll see the west temple, the highest peak in Zion," intones the driver as we make our way down the lane at a stately 21 mph. "The three peaks coming into view on your left are Abraham, Isaac and Jacob, the famous Court of the Patriarchs.

"Next stop, Court of the Patriarchs. Please collect your personal belongings."

We are commuters into the wild. The schematic route map on the wall of the bus reads like an outdoors version of the Orange Line: Canyon Junction, Court of the Patriarchs, Zion Lodge, the Grotto, Weeping Rock, Big Bend. Instead of a "Got Milk" ad, there's a natural history poster: "If perched in the middle of this bus, the golden eagle's wings would stretch from wall to wall."

"What's our stop?" asks a boy in a Baltimore Orioles cap.

"This one," says his father, Gene Marquis, a Navy engineer from La Plata who's here with his wife and two sons during a two-week western park swing. They hadn't heard about Zion's unique shuttle system before showing up this morning, but so far they're loving it. "It's great. When I'm driving, I can't see anything because my wife keeps telling me to watch the road. I like that they actually tell you what you're seeing."

The Marquises scramble off along with several other families, and I follow. The shuttle is propane-powered, and it pulls away with something less than a roar -- more like a soft grumble and a whiff of outdoor grill. Not another vehicle passes, and an exquisite desert silence fills the void, broken only by the soft mariachi shake of leaves from the cottonwoods along the river.

I've visited Zion once before, in the summer of 1999, and well remember the buzz-kill crush we'd found on this same route. We had hoped to actually walk on one or more of the trails, but it would have been easier to find parking in Georgetown on New Year's Eve than in any of the small, jammed lots in this canyon. Eventually we did what everyone else was doing: double-parked on the roadside, flattening a bit of desert vegetation in the process, and walked almost a mile through traffic just to get to a trailhead. Like many national parks, Zion was being loved to death by drivers like me. And short of banning cars from the most popular road in the park, it seemed there was nothing to be done.

But, amazingly enough in this era of intractable problems, they did something. Starting the very next year, the Park Service launched a radical pilot program that has, by all accounts, transformed the visitor's experience. From April through October, the park actually does ban private cars along the six-mile scenic route, along with motorcycles, tour buses and RVs. The only way to the park's most popular sites is by foot, bicycle or one of these free shuttles that run like clockwork from 5:35 a.m. to nearly midnight.

Visitors park in one of the lots by the visitors center or in the adjacent town of Springdale, less than two miles away. A second free shuttle loop connects spots all along Springdale's main street with the park, allowing visitors to ride door-to-trail from their hotels and making this village of 500 Utah's smallest town with a full-scale mass transit system.

In spite of some initial local opposition to closing the road in summer, both Springdale and the Park Service now consider the shuttle a boffo success. Visitation hasn't declined, and the park reports that a whopping 98 percent of recorded comments are favorable. Officials from parks around the country and as far away as New Zealand have come to see how they got the cars out of Zion.

"It was just an immediate, dramatic difference in the way visitors could enjoy the park," says Ranger Haraden. "The very first evening, a mountain lion crossed the road in front of a shuttle. I took that as a good sign."

Under the gaze of the "Patriarchs," the Marquises and I stand at the silent roadside, enjoying the phenomenon of a dead-silent national park on a glorious peak-season morning.

"It would be chaos if everybody drove back in here," says Paula Marquis. "I guess this is the way all the big parks are going to go."

She might be right. Mass transit is nothing new in national parks. According to the National Parks Conservation Association (NPCA), 96 units of the park system operate some kind of alternative to the one-family/one-car model, from the ferryboats of San Francisco's Alcatraz, Michigan's Isle Royale and the Statue of Liberty to the shuttle buses, vans and trolleys in parks such as Denali and Glacier Bay in Alaska. And as more people try to wedge more cars into the most popular parks, observers say shuttle systems similar to Zion's will almost certainly become more common.

"You have to look at each park individually, but everybody thinks it's going very well at Zion," says Gerry Gaumer, a Park Service spokesman. "It could be a good model to follow."

"Absolutely," says Laura Loomis of the NPCA. "A lot of parks could benefit from a system like this."

Acadia National Park in Maine already has a voluntary shuttle, paid for in part by L.L. Bean, that brings visitors into the park from Bar Harbor. The free service has proven hugely popular, cutting summer traffic congestion and reducing park pollution by as much as shutting down one power plant would do, Loomis says. At Harpers Ferry, W.Va., visitors leave their cars at remote lots and ride buses down into the cramped little mountain town. And shuttle systems are on the planning boards of several of the biggest and most popular parks, including Yosemite, Grand Canyon, Yellowstone, Grand Teton and Great Smoky Mountains (see story on Page P4 for details).

Each of these parks faces its own set of traffic problems, and none is likely to get a Zionlike mandatory shuttle along with a ban on cars from the park's interior, even seasonally. (The Cades Cove area of Great Smokies, a one-way, 11-mile loop with overwhelming congestion, is one that may opt for the full Zion). But each park still faces hard opposition from local businesses and officials who fear that Americans won't visit a park that doesn't welcome their cars as well.

"They should come here and see," says Dean Cook, general manager of the Best Western Zion Park Inn in Springdale, and president of the Zion Canyon Visitors Bureau. A shuttle stop sits right in front of his motel, and a group of his guests wait there for the bus. The local opposition largely vanished, he says, once the tourists embraced this new option so heartily. "The impact of the shuttle has been terrific. The ambiance has completely changed. You can actually hear the river running."

Back inside the park, I hop on and off the shuttle system like a Gray Line tourist with an all-day pass. On a bus with a huge bat posted on the side, the driver rattles on about the surrounding geology: "The Navajo sandstone is only 89 percent solid. The rest is water that filters very slowly through. The water continuously seeping from Weeping Rock has been dated to be 4,000 years old.

"Next stop -- Weeping Rock."

I step off and climb up the short trail to the mossy overhang where old, old water drips out of the rock onto my face. By the time I get back to the road, another shuttle is pulling up, this one with a lizard on its side. It's full, and just after I squeeze into the last seat, a young family of six climbs up. The father sees the crowd and looks as if he might back down the steps. But his littlest girl, about 7, cries, "Oh boy, we get to stand!" and on they come.

They are the Arnell family, from Camarillo, Calif., and in spite of not getting seats every time, they've embraced shuttle life. "It's like a ride for the kids," says mom Liesl, 30. "It stops right by our campground [near the visitors center], and we just jump right on."

Eventually, I do follow Ranger Anderson's advice, and get off at the Grotto stop for the two-hour climb up to Angels Landing. It's a beautiful scramble (about half of it through a cool, narrow rift called Refrigerator Canyon) and a surprisingly tricky one. "This is one of our most strenuous hikes," the shuttle driver had said. "It's not for those with a fear of heights." The last few hundred yards of it are along sheer drops of the certain-death variety, with chains bolted to the rock to provide a physical handhold and some mental hand-holding, too.

But the payoff is worth it, a sweeping north-south view of a canyon that has taken the breath of human visitors since the days of the Paiute Indians. Way down below, the ribbon of highway lies along the gray-green Virgin River. It's empty except for two toy shuttles I see slowly passing each other on a bend in the road directly below. They make not a sound that travels this high.

Two hours later, with a hint of dusk in the air, I climb back on the faithful shuttle and ride one stop to the Zion Lodge, an austere but comfortable hotel spectacularly situated between high canyon walls. Guests at the lodge are given a pass to drive into Zion, but only to unload their luggage and park. Unlike my visit here six years ago, when traffic around the lodge looked like a stadium parking lot after the Super Bowl, it was now as calm as an ancient glade.

On a clear evening like this, with no backed-up traffic, the outdoor patio of the lodge's Red Rock Grill may be the most pleasant dining room in the country. After a fine (and not expensive) meal of breaded eggplant and tomatillo, I watch the sun slide up the cliffs, giving the canyon over to the night once again.

Suddenly, a white cottonwood tuft floats down in a moment of still air, dropping on a plumb line into my glass of California zinfandel. I count it as a bit of sanctified manna and drink it down, a spontaneous communion in a natural cathedral that is, once again, as silent as a church.

Zion National Park, in southwestern Utah, was once clogged with summer traffic, but a ban on cars and the addition of shuttles has freed up the six-mile scenic route. At Zion National Park, in southwestern Utah, summer traffic jams are history since the park decided to ban private cars and only allow hikers, bikers and free shuttle buses along the six-mile route that includes the Narrows (left) and Weeping Rock (right).The park shuttle offers visitors access to the canyon and Zion Scenic Drive. At Utah's Zion Canyon Visitor Center, you can leave your car for the day and explore the park by foot or shuttle.