I saw the Rio de Janeiro gondola system [0] on Brazil with Michael Palin [1] a couple of days ago, and spurred on by the fact I've always enjoyed travelling on these systems, I began searching out more information about them around the world. I found a fantastic (for transport wonks :-) website called the Gondola Project [2] which has a vast amount of info (there's a link to it buried in the OP Wired article) about all the different types of systems and which circumstances they fit best. It also mentions the several aerial ropeway urban transport systems that are in successful operation around the world, such as Medellin, Colombia; Caracas, Venezuela [3]; Constantine, Algeria [4]; and Villa Nova de Gaia, Portugal [5].

To the commenters here saying "why can't they just make huge suspended buses", apart from the obvious engineering loads that entails, the problem is mostly that this means the gondolas have to stop at each "station" so that a decent amount of people can embark/disembark.

The most common modern gondola systems are built with MDG (monocable detachable gondola) technology, though the state of the art is the 3S (or TDG - tricable detachable gondola). More cables makes a 3S system more expensive, but makes the gondolas much more stable in higher winds, and allows them to travel faster along the line as well.

In these systems, many small gondolas flow in a continuous system, but are detached from the cable and slowed at stations so people can embark/disembark. This allows the main pull cable to always run at the same speed, which conserves energy and keeps all other attached gondolas moving. It also allows for corners (!) in the line (though a station must be located at the corner), as gondolas can be detached at a station, moved around by the required angle as they load/unload, and then reattached to the new cable which takes them off in a new direction. For a good example of this, see the Rio de Janeiro system mentioned above. Junctions can even be implemented this way if required (though the logistics would be interesting).

Rescue issues – most of these urban systems are designed to run over accessible areas, and no higher than 2-4 storeys from the ground, so if rescue is needed Fire Department crews can use standard equipment to reach the stranded gondolas.

Some commenters on the Wired article mention the Portland Aerial Tram system, and various disappointments around it. Aerial trams are different from gondolas in that there are normally only two cars, which move in opposite directions simultaneously, so each must be stopped at the same time, and any mid-point stations must be equidistantly located, unless you are happy having one car stopped in mid-air while the other is at a station. For examples of this with funicular railways, see the Innsbruck Hungerburgbahn [6] or the Wellington (NZ) Cable Car [7]. The main limitations on this kind of transport are slow load/unload times (hence longer passenger wait times), inflexible station layout requirements, non-detachable gondolas means no cornering etc.

Someone mentioned the "scared of heights" issue – my partner is scared of heights, but she was fine travelling on a gondola system similar to all these at Taronga Park Zoo in Sydney, as well as on the Nordkettenbahnen, the aerial tram in Innsbruck that takes off from the top of the Hungerburgbahn. Of course, YMMV. A system that probably _isn't_ good for people with a fear of heights is the new Stanserhorn Cabrio (stunning pic [8]) [9].

For (even more) info, The Gondola Project website has a big section called "Learn about cable transit" - fascinating stuff [10].

[0] http://www.wired.com/magazine/2011/02/st_riogondola/

[1] http://en.wikipedia.org/wiki/Brazil_with_Michael_Palin (Episode 3: The Road To Rio)

[2] http://gondolaproject.com/

[3] http://gondolaproject.com/2010/03/11/medellincaracas-part-1/

[4] http://gondolaproject.com/2012/07/19/constantine-telepheriqu...

[5] http://gondolaproject.com/2011/04/08/new-urban-gondola-opens...

[6] http://www.nordkette.com/en/cable-railways.html

[7] http://en.wikipedia.org/wiki/Wellington_Cable_Car

[8] http://dl.dropbox.com/u/24956/stanserhorn_cabrio-opening_day...

[9] http://www.stanserhorn.ch/en/travel/cabrio/

[10] http://gondolaproject.com/learn-the-basics-what-is-cable-pro...