The Aiguille du Midi cable car in service with Mont Blanc in the background in Chamonix, France. (Brian Yarvin/FTWP)

There’s a metallic clang, and the door slams shut. Seconds later, the crammed cable car whisks upward, heading for La Flegere, a mountain just outside Chamonix in the French Alps.

A pit forms in my stomach as the car starts rocking. After a few moments, it’s swinging so enthusiastically that one man almost falls, and the kids on board are squealing with delight.

Most of the other passengers focus on the stupendous views. It seems as though I’m the only one who doesn’t calm down quickly and enjoy my day on the mountain. But not being a cable car regular, I find a host of unsettling questions popping up in my mind: How do these contraptions work? How did they get all this stuff up the mountain in the first place?

And the all-important query: Are these things safe?

A few days later, I took another cable car from Chamonix up to Aiguille du Midi, a far more frightening-looking ride to a much higher spot. When we reached the mountain, all the other passengers ran out to the viewing terraces. But I was stopped dead in my tracks by a diagram that explained exactly how the whole thing works. This is what I wanted to know.

I studied the diagram carefully. There’s a motor, of course, but it alone can’t simply lug the car up as dead weight, so each cabin going up is counterbalanced by one going down. This is done by mounting each one halfway around a loop of steel cable. Now, obviously, most lifts have more than two cabins, but the idea of even spacing and counterbalancing cleared things up for me in a big way.

At the top and bottom of the lift, the cable spins around large discs called bull wheels. One of those wheels is powered, and it pulls the cable along as it turns. The other wheel is known as the return, and it sends the car back the other way. Drum brakes, not unlike those in older cars, can stop the wheels that carry the cables, and emergency brakes on the bull wheels offer a backup.

There was one more piece to the puzzle: What keeps the cables on the bull wheels in the first place? Wouldn’t they just pop off when they expanded in warm weather? And what corrects for a heavily loaded car going one way and an empty one going the other?

It turns out that this is handled with huge underground counterweights that pull back on the bull wheels and keep the cables at just the right degree of tension.

All in all, a pretty nifty piece of engineering.

In fact, it was the invention of lifts that made skiing popular. Before then, people would have to hike up mountains to ski down them. The idea that you could have more than a few downhill runs a day was revolutionary.

* * *

Although skiing has existed in one form or another for thousands of years, motorized lifts have been around for only about a hundred. The first known working lift was apparently in the Black Forest town of Schonaich, Germany, where a water-powered tow rope for skiers and toboggans operated during the winter of 1908. It took a bit longer for lifts to catch on in the United States, but by the mid-1930s, tows rigged from old auto parts were fairly common in New England.

Similarly, cable cars of some sort have been used in mining for several hundred years, but it wasn’t until the turn of the 20th century that they were introduced for passenger use. In 1907, one of the earliest passenger tramways opened at Sunrise Peak, Colo., to carry tourists up the mountain. It operated for only a few years, but two others, opened in 1913, set the stage for future development. The first, at Sugarloaf Mountain in Rio de Janeiro, ascended to a legendary tourist spot; the other, at San Vigilio, Italy, climbed from a large village on a steep slope to a smaller, higher one with winter sports facilities. Although they’ve been updated with more modern equipment, both routes are still in operation.

In the United States, things took a big step forward with the opening of the first chairlift at Sun Valley, Idaho, in 1936 and Cannon Mountain Aerial Tramway near Franconia, N.H., in 1938. The chairlift was created by a company that produced aerial tramway-like conveyors to transport bananas from tropical plantations to ships for export. The simple chairs hanging from a cable made it possible to travel much greater distances than one could when being pulled along by rope. Cannon Mountain took things a step further; that lift had enclosed cabins. (Sunset Peak had tiny open cabins.) Skiers were carried up the mountain without being exposed to the elements. Building these lifts was tough. At Cannon, dozens of men carried materials such as steel cable and cement up the mountain on their backs. A daunting task.

By the ’50s, both the sport of skiing and the business of tourism had exploded. Ski areas opened or expanded across Europe and North America and brought in crowds of new visitors. Cable lift construction, however, was still handled by men and mules. According to an exhibit in a Chamonix museum, the tramway to the top of the Aiguille du Midi, finished almost 20 years after the one up Cannon Mountain, features a main cable that was hauled into position by a team of local mountain guides.

* * *

Okay, so I’d gotten the hang of how aerial tramways work. But now I found myself facing the next big question: Just how safe are they? Tales of lift and aerial tramway accidents appear to be legion, but I wanted the real story.

First, the big number: There have been 12 fatalities on U.S. ski lifts since the ski industry started keeping records in 1973. The numbers in Europe have been slightly worse, largely because of two major accidents: one in Cavalese, Italy, that killed 42 on March 9, 1976, and another in the same place that killed 20 in 1998.

Still, these numbers aren’t vast, and I felt reassured. Fatalities don’t seem to be anything to worry about excessively. But what about “lesser” incidents, such as the one at Maine’s Sugarloaf Mountain Resort last year, when a chairlift cable jumped off its track and five chairs loaded with skiers fell 25 feet to the ground. Thanks to the previous day’s 22-inch snowfall, there were only eight injuries.

Apparently there’s no national clearinghouse for such data. According to James H. Chalat, a Colorado lawyer who specializes in ski injury law, “Most states have a self- reporting system.” So I attempted to contact some state regulators, but none responded, leaving me with the feeling that things are far more dangerous than the number of incidents would indicate.

But as I studied incidents serious enough to be mentioned in even local news media, it became clear that mechanical failures such as the one at Sugarloaf are reported in the English-speaking world on average about once a year. Which means that lift and tramway riding is probably far safer than either driving on snow-covered roads or even skiing itself.

However, I was surprised to learn about a whole other category of ski lift accidents: those caused by skiers and staff members not paying attention at lift loading and unloading areas. There’s a lesson here: Follow instructions carefully and know the proper techniques for boarding and exiting lifts.

* * *

These days, cable cars and aerial tramways (actually, the terms are synonymous) are in more than just ski resorts. They’re found all over the world — crossing the harbor in Singapore and spanning a gorge to reach an ancient monastery in Armenia. Even in areas known for skiing, they’re tourist attractions in themselves and provide rides up to mountaintops for para-gliders and backcountry trail access for hikers and mountain bikers.

Armed with my new understanding of how the lifts work, I decided to test my courage on the aerial tramway between Manhattan and Roosevelt Island.

No, neither of these places is known as a destination for skiers, backpackers or mountain bikers, but besides being relatively close to home, the cable car that connects them is high enough to have been used in episodes of “Fear Factor” and was recently rebuilt by the company that refurbished the Aiguille du Midi tramway in Chamonix.

At the tram terminal on 60th Street, I was able to recognize the basics, such as the cables running around the bull wheel. But there was a big difference here: The Roosevelt Island tram is suspended from two cables, not one. Typical for cars this big, a third cable that bears no weight does the pulling.

I pondered this while boarding with a crowd of typically nonchalant New Yorkers. There was none of the fascination or wonder that I’d seen in the Alps. Yes, the tram rocked back and forth in the spitting rain, but even the elderly and the disabled seemed more interested in their newspaper crossword puzzles and e-readers than the ride.

It may not have been the Alps, but the view of the cloud-shrouded city at twilight was pretty awesome. The wind howled, but these New Yorkers didn’t even look out the window. It was the same crowd you’d find on a New York City subway train, only high in the sky, suspended from two thin steel cables.

Finally, a young boy pointed at his friends and yelled, “If this thing stopped up here, which one of you would I eat first?”

Whew, I thought. Somebody else, even if it was a little kid, was scared.

The operator cracked the smallest bit of a smile, and a moment later, we reached Roosevelt Island. The exiting riders looked as if they were getting off a bus.

Smugly joining everybody else, I walked out of the terminal wondering how a ride like this could frighten anybody.

It was no big deal at all.

Yarvin is a writer, photographer and avid backpacker from central New Jersey who has hiked in the Alps for more than 25 years.