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S400: Glass Bubbles in the Sky

2011 September 21
by Matt Gangemi

< Rio de Janeiro; photo by SEASDH via Flickr >

What if I told you that I had a transportation system that can move the person equivalent of 40 buses in each direction.  This system is elevated above traffic, and can hop over freeways with ease.  It has a vehicle frequency of well under a minute.  It requires very few operators.  It can span over waterways with supports potentially set over a mile apart.  It can climb hills almost without limitations of a maximum slope.  It has a very small footprint with very few supports required between stations, and stations can be built right into buildings.  It’s completely electric, but can continue operation in a power outage using integrated backup generators.  It can load wheelchairs easily, and bike racks can be added.  It has decades of use in thousands of locations around the world, with a high safety and low maintenance record.  Enough systems are built that even the stations themselves are off-the-shelf components.  Yet it’s so cheap that South American cities that are usually known for their Bus Rapid Transit systems can afford to set up vast networks.  And Seattle already had this technology but gave it away.  [picture:  Seattle’s Skyride, now in Puyallup]

If you haven’t guessed yet, I’m talking about gondolas.  There has been a recent trend around the world to install them not just at ski slopes and amusement parks, but as major urban transit systems.  They are ideal in built-up cities with hills, waterways, or highways, but are cost effective in any city thanks to the low cost of construction.  The only construction required is at stations and towers – there are no roads, ramps, tracks, or tunnels to build.  They are relatively slow (~14mph for the inexpensive detachable monocable, ~17mph for a 2-cable gondola, and a bit faster for the 3-cable system) so they’re not appropriate for long-distance transit, but since this speed is in a straight line over traffic and terrain and because there is no wait time between vehicles it can dramatically decrease travel times.  [picture: Station Zu of the Sentosa Island Gondola.  Built in 1974 on the 15th floor of an office building.]

< Singapore; photo by ashkyd via Flickr >

Let’s take a sample Seattle route with 3 stops.  Seattle Center to South Lake Union to Capitol Hill near light rail.  Each of these neighborhoods is separated by highways and geography to such an extent that put the peak scheduled bus time at 40 minutes for this route – and add time for waiting, since traffic makes this route unreliable.  But a gondola could make this entire trip in 7 minutes with no waiting.

The problem I’m trying to solve is connecting neighborhoods together, to make a city easy to get around in without a car.  There are many solutions to this problem, but a gondola system is the cheapest solution and would be fast and easy to install.


Matt Gangemi, PE, is a mechanical engineer, and for the last decade has been designing and analyzing efficient mechanical systems for buildings.