Cable cars are a transportation system composed of a series of cars suspended from thick cables supported by large, widely spaced towers. The name can be confusing in an American context, where it generally refers to cable-drawn rail cars such as the trolleys of San Francisco; instead, such systems are often referred to as “chairlifts”, or (this is cute) “gondola lifts”.

Whatever you call them, the technology has long been used at ski lifts, and they’re a favourite attraction at amusement parks as well. But recently, they’ve found a new application: public transport.

This new wave of urban chairlift construction kicked off in Medellín, Colombia, which introduced the new system to serve underprivileged hilltop neighbourhoods. Each line was given a letter and colour, in a move which deliberately echoed the branding of the city’s existing metro system.

Construction of the new system, the Metrocable Medellín, was completed in 2004. Soon, the idea caught on across Latin America, and cable cars began hauling passengers in major cities such as Caracas, Manizales, Rio de Janeiro, and most recently La Paz, Bolivia.

The official map of Medellín’s tranpsort network, showing traditional metros, cable cars and bus rapid transit lines.

It’s easy to understand why these systems draw so much attention. Unlike buses, which grumble along at street level, and subways which are buried out of sight, cable cars soar majestically above the cityscape, offering dramatic views to riders.

But the reason they’ve taken off in Latin America, and especially in mountainous cities where informal developments tend to concentrate on hilltops, is for their ease of construction over steep terrain. Bus-based public transit is often unreliable or unavailable to slum dwellers, and in hilly neighbourhoods buses are slowed by twisting streets. Cable cars, by contrast, glide effortlessly over these areas.

Such systems have in many cases been created with the express purpose of making life better for people living in slums, while showing respect for the autonomy of such communities. Arturo Brillembourg, an architect with Urban Think Tank and one of the developers of the Caracas Metrocable, said in an interview with Architonic: “Our concept is based in architecture that has the ability to change according to the transformation of the informal city and the dynamics among its inhabitants. We only provide the framework for future adaptation.”

These noble ideas of community empowerment are echoed by the writing on the cars themselves, emblazoned with bold slogans like “social ethics”, “participation”, and “love” (also, simply “Venezuela”). Cars in Medellín aren’t so outspoken, but their human representatives are. A headline from the website El Colombiano proclaims: “The Metrocable is quality of life”.

But the cars are not without their technical drawbacks. First, their capacity is much lower than conventional mass transit: a system designed for high capacity can typically haul 3,000 people per hour in each direction, which sounds like a lot until you consider that the same number of people can be carried by just three subway trains. They’re also slower than conventional transit, ambling along at 10 mph (16 kmh), the speed of a leisurely bike ride. And then there’s the safety issue. While proponents maintain that chairlifts are statistically very safe, the idea of dangling in a car suspended hundreds of feet above the ground from a cable no thicker than your wrist is still enough to make many riders squeamish.

The public response to these systems has varied. In Medellin, it’s been one of almost unanimous support: proponents boast of sharp drops in crime and increases in investment, crediting it as one of the keys to the “Medellin miracle” in which the city turned itself around after widespread drug-related violence in the 80s and 90s. In Caracas, the cable cars have become so much a part of daily life that users angrily lashed out after an unannounced closure in late 2012. La Paz’s system seems to be doing well, too; despite initial concerns about price, a report last month found the system to be a success.

Those in Rio de Janeiro have been somewhat less successful, however. A report from the website Rio on Watch noted that ridership was lacklustre, despite the fact that the line has worked well for some residents of the Complexo do Alemão favela that it serves. It also cited transportation specialist Raul Lisboa, who claimed that system in its current state does not effectively cover all areas of the favela.

The biggest failure in the use of cable cars isn’t anywhere in Latin America: it’s in London, where the Emirates Air Line across the Thames was constructed in 2012 to much fanfare in the lead-up to the Olympics. Today, the line serves a fraction of the people who took it during the games; the Evening Standard reports that the line only gets four regular commuters per day.

Urban cable cars are relatively new – but even from their short track record, it’s clear that they excel in some situations but fail in others. Let’s hope that the planners take this into account, before the next wave arrives.

Credit for image of Metrocable cars above a Medellín street: Jorge Gobbi, via Flickr, reused under creative commons.