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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.

24 Responses leave one →
  1. Bill Bradburd permalink
    September 21, 2011

    great piece and shows some solid out of the box thinking.

    the first hill/B’way streetcar at $200M or whatever should have instead been a system of gondolas from downtown up. would have served more people for less money. a streetcar on Broadway seems silly – it’s one of the most walkable streets in the city. with all that transit investment i’d expect to hear calls for 85-125 feet building there.

    while you’re at it Matt, can you plug some counterbalanced cable car lines, say on Dexter, Queen Anne Ave, etc…

    • Matt Gangemi permalink
      September 21, 2011

      I hereby call for 85-125′ buildings there ;-)

      I could be convinced about a First Hill gondola, but streetcars have their place as well. They’re especially great in areas where you want frequent stops. A gondola line will get you to the neighborhood, and you walk from there (since all of the cost is in the stations, where in a streetcar the stations are cheap). That said, there would be value in getting you up the hill quickly, even if you had to walk once you were there.

      I’ve been pushing for a counterbalance up the Counterbalance for years. It wouldn’t be difficult or expensive once we brought s streetcar line there.

      My favorite cities use different transit tools for different jobs. In Istanbul you can take a light rail line through the city, get off to take a Funicular up a hill, then ride a streetcar on an almost pedestrian-only, very walkable street. I’m imagining the automated voice now on a future light rail line: “Capital Hill Station. Gondola connection west to South Lake Union and Seattle Center. Streetcar connection south to First Hill and the International District.”

  2. Giorgio Betteto permalink
    September 22, 2011

    Regarding the line on Harrison street , if is possible (and useful) to have even-spaced stations, you could have more than three stops and spend much less money by using a “Pulseè” gondola, that have fixed grips cabins in groups . The capacity could be near to a MGD but cost less than half, with advantage in loading .

    • Matt the Engineer permalink
      September 22, 2011

      You’re value engineering my plan before it’s even a real project! It’s certainly possible (we could put a mid-block over-the-street station in SLU if needed), but I’m not sold on fixed grips. I find frequency to be much more important than capacity, and I think Portland probably did their aerial tram wrong. Since frequency is limited by the number of vehicles, cutting back to 4 vehicles makes the frequency about every 4 minutes for this route. To keep capacity the same, this drives up the vehicle size. Driving up the vehicle size drives up the station size, and the tower size. So I would think you’d end up spending more for a system that isn’t as functional or expandable. I would guess the reason Portland’s aerial tram ended up in the 40 million dollar range is because they went to fixed grip.

      For those that are curious about technology options for gondolas, check this site out, and click the “Learn About Cable Transit” for more.

  3. Giorgio Betteto permalink
    September 22, 2011

    You have to consider that urban gondola need a “little tweaking” … for example, the acceleration usually allowed is roughly a 1/3th of that allowed in a Metro or light rail, and for this in a Gondola you practically doesn’need to have a grip to stay upright .. try this in a Metro!

    allowing slightly more acceleration you could well have a 5 m/s global speed for a pulseè , and you could have a convoy of 4 cabins of 12 places each every 2’45” – roughly 2000 p/h
    considering as stops Key Arena – Aurora av./Harrison – Cascade Patch – Broadway
    pulseè stations are very short respect detachable, since the acceleration and deceleration are done on line, not in station, so inside the current station lenghth of an MGD (more or less 25/30 metres) you could easy make stop inside even 8 15 people cabins.

    The key point is the equidistance of the stops – just one different and the system won’t perform.

    • Matt the Engineer permalink
      September 22, 2011

      I was looking more for 3 stops, the third being between Westlake and Terry (the two streets of the streetcar line).

      Checking out my route, an equidistant station would be only 1/2 block from the place I put it – though that’s only looking at the horizontal dimension and ignoring the slope up to Capital Hill.

      I’m still not convinced – a detachable gondola would offer more flexibility and frequency. But if the cost difference is substancial I could be convinced.

  4. Eric L permalink
    September 23, 2011

    Considering that it is 3 minutes (projected) by rail from Capitol Hill to Westlake Center and 4 minutes by monorail from there to Seattle Center, and both run pretty frequently, I guess I’d wonder 1. How does the cost of this compare to the cost of buying the monorail and integrating it into our transit system? 2. Is it justified by the mobility benefits for SLU alone? 3. If it’s justified by mobility for SLU primarily, perhaps there should be more stops in the SLU area? 4. Given the steepness of the hill at I-5 and how much it obstructs pedestrian mobility, perhaps there should be a station on each side of I-5 to create a new way to cross it and to make sure people only need to walk downhill to get to/from stations?

    • Matt the Engineer permalink
      September 26, 2011

      More stations are certainly possible, but I was minimizing stations to minimize costs and maximize speed. Add another minute travel time and a few million dollars per station. My general strategy was to pick a point in each neighborhood that’s easily walkable from high density areas. If this ever becomes a real project, we’d need a good potential ridership study to decide if we need more stations.

      Regarding Link/Monorail, add wait time in there – your average wait for Link will be 3.5 minutes, and another 5 minutes on the Monorail. But you’re right – the main benefit is connecting SLU to, well, anywhere.

  5. September 24, 2011

    Matt – Great idea. I wish gondolas were considered in the Transit Master Plan. The costs are similar to streetcars, but they can provide routings that are not possible with any other transit method.

    Two thoughts about this routing:
    1. Is the middle of the Seattle center the best place for the line to begin? The monorail’s location in the center of the center renders it almost useless for actual mobility from surrounding neighborhoods. Its quicker and easier to catch a 1, 2, or 13 bus (along the west side) or a 3, 4 or 16 (along the east side) than to walk to the monorail station in the center and wait around to buy a ticket. I would consider extending the gondola two blocks further west to Queen Anne Ave., or shortening it to end at 5th Av N. Center-goers still have convenient access, but Uptown residents and/or Gates Foundation employees will find it convenient also.

    2. On the east end of the line, would it be worth it to have a turning station and travel two blocks south to directly meet the Link subway station? It should be considered in planning, but I am not sure the benefit would exceed the additional cost.

    • Matt the Engineer permalink
      September 26, 2011

      1. I could bring it to 1st or QA Ave, but I was afraid of going over Key Arena. It wouldn’t be too tough to have the towers tall enough, but I assume at some point they’ll replace the Key Arena, and I didn’t want to limit the future building’s height. I suppose we also could route the wires around the Arena.

      I will mention that this location is only a block from a major bus stop on 1st, and makes an enjoyable walk from both the Monorail and the Gates Foundation buildings.

      2. Yes. I wanted to keep it simple, and the walk is very short and enjoyable to the light rail station, but we could certainly put in a turning station and connect directly to rail.

  6. Rob K permalink
    September 26, 2011

    You’ll enjoy this site,

  7. Giorgio Betteto permalink
    September 27, 2011

    @Matt : at this link you could download a program to calculate approx. costs of gondola and ropeways .

    Its in Italian, but should’nt too difficult to understand with a dictionary. Its based on Bolzano Province official data (2006 -08 based, so need to be correctd)

    • Matt Gangemi permalink
      September 27, 2011

      Great resource Giorgio! Time to practice my Italian.

    • Matt Gangemi permalink
      September 27, 2011

      Ok, I had to translate most everything (it’s been an entire decade since the language CDs).

      € 4,982,916 = $6.8M. Includes: electromechanical works, construction works strictly indispensable to cableway, transportation, installation, utility connections, electrical measurements, stakeout, construction management, architectural design, testing, other.

      • Giorgio Betteto permalink
        September 27, 2011

        Correct : add a 25-35% general price increase from 2006.
        Architecture is considered the usual “slim line” of most gondola or chairlifts, with an underground/base floor in reinforced concrete and up the ropeway machinery enclosed in streamlined covers.
        “Real” station building cost may increase a lot.

  8. Shea Kauffman permalink
    April 27, 2012

    I’d really like to see one of these planned for the U-villiage, U-district, Wallingford, Phinney, Ballard . 45th is the worst street to drive on during rush hour

  9. February 20, 2013

    Wow, not a bad idea. At first, I thought gondolas were those floating hot-air balloons, so I was skeptical, but now I see.

  10. clew permalink
    February 21, 2013

    Surely these *ought* to be little dirigibles tethered to lines between lightweight stanchions. I don’t think any other city has those, no? We could be truly World Class.

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