30 January 2014

Sky-borne urban transport: introducing the FlyWay and the FlyPod

In a blog-post about one year ago I wrote about how ridiculously expensive it is to build underground transport in existing high-density cities and how much better it would be to transport people and things in the airspace over existing streets and other free space. I also wrote that elevated railways (including monorails) and elevated roadways are unacceptable in people-friendly dense cities, because they create too much noise and remove precious daylight from the streets below.
I have also discussed that hovering, flying, or floating in the air are all impractical for urban transit vehicles, so we have to find some kind of support structure to hold unto, but which takes up as little airspace as possible. Obviously, the smaller and lighter that structure is, the smaller and lighter all the vehicles have to be. This brings us to the question: how light can people-transportation vehicles possibly be? Here are some numbers:
  • Bicycle: 10 to 15 kg
  • Velomobile (fully faired, recumbent bicycle): 30 kg
  • Motor Scooter (electric or combustion engine): 50 to 200 kg
  • SegWay: ca. 50 kg
  • Renault Twizy (faired two-seater, electric): 450 kg
  • Mercedes Smart (two-seater): 730 kg
  • ULTra PRT vehicles (Heathrow Aiport, 4 seats): 850 kg
  • SUV car: up to 2000 kg and more
As you can see, light vehicles like bicycles can transport up to ten times there own weight, while the heaviest ones often transport less than even a tenth of their own weight (because the usual load is much less than the permitted maximal payload).

Thinking of transit you'll probably think of large buses and train cars which weigh several tons a piece. Those will obviously be too heavy for a light-weight approach. But don't worry about getting enough transport capacity in our system: instead of big vehicles with big gaps in-between them, we'll just have to make sure that our small vehicles can draw really close and even form emergent trains without any coordination.

Using this idea we can design a vehicle, our FlyPod, to transport people together only if they really want to travel together, not (unlike buses or trains) if they just happen to travel in the same direction. The minimal payload would then be just one person with clothing and keys while other luggage could already be transported in a separate, trailing, vehicle. However, there is lots of convenience associated with having your luggage with yourself and furthermore, if the vehicle has enough space and the seating flexibility, this space could be used for either a second passenger or for some luggage! Taking this into account our design payload would be 200 to 300 kg depending on the country of usage. (People sizes and weights vary quite a bit in the different regions of the world.) The empty weight of the vehicle would then be between 50 and 150 kg depending on other factors of the design. 

Note particularly that the resulting overall loaded weight is much less than that of typical areal lift vehicles (gondolas) which usually transport between 4 to 20 people per vehicle. And there we have the solution to our problem: just hang the vehicles on cables! Cables are so slim that they are almost invisible and small pedal-powered or electric vehicles running on those cables with less than 50 km/h will not make much noise. Supports will have to be spaced closer than for areal lifts (because vehicle density is higher), and they will have to be a bit sturdier than those built for streetcar overhead-wires, but otherwise they can be customized and integrated into the urban landscape adapting to whatever style is already present. And that's the FlyWay on which our FlyPods will travel!

FlyPods bring cycling to a whole new level

I have to admit that I personally prefer the pedal-powered variant because I love bicycling myself. It actually has so many advantages compared to a regular bicycle that it becomes a whole new experience. The best thing for me is that a passenger does not need to stop at red lights and crossings, you don't even need to look out for traffic! You could be reading on your phone, playing on your tablet or just gazing out the window for the whole trip! Totally like in a taxi except that you have to pedal a bit. And the pedaling will be easier, too, since most of an ordinary urban cyclists power is used for accelerating themselves after a stop. But if you don't stop, you also never waste energy for braking and speeding up again! Also, even though the vehicle is a bit bigger than a normal bicycle the recumbent position and the fairing make for a very aerodynamic shape which doesn't need much more power than a bicycle to get moving. In fact, vehicle weight only matters when accelerating and we just need to do that one single time per trip. (And there's help for that too, as we'll see later.) The next advantage is that you are protected from rain and wind and even excess heat, since a simple yet effective cooling system could be powered by solar panels on the vehicle roof. (The sun creates the heat, so it's always available when we need energy for cooling!) Fleet management of the FlyPods is very similar to how public bicycles (like Paris' famous Velib and numerous others around the world) are managed except that empty FlyPods can be moved around in little trains along the wires itself without taking up any extra road space for maintenance vehicles. If a station has surplus empty vehicles which need to go somewhere else, these can even be just pushed onto the main FlyWay and then pushed around by other vehicles, but this leads us to the next exciting topic: emergent trains and smooth merging.

Emergent trains are very simple to explain: since we are dealing with slow vehicles that have no obstacles on their way except other vehicles of the same sort (which in turn have no obstacles in their way...), a train simply forms by a faster vehicle bumping into a slower one! This bump is cushioned of by springs in the vehicle ends which contract as the vehicles approach and slowly expand again as the front vehicle gets pushed and the rear one consequentially slowed down. The spring also compensates for the normal small variations in pedaling power which would otherwise result in repeated bumping into each other. The nice thing about those emergent trains is that the air resistance of two closely travelling vehicles is almost the same as for a single one. In other words, not only the front vehicle profits by being pushed, but the follower also profits because they now have less resistance to overcome.

Smooth merging is also simple and it is necessary to keep vehicles from stopping at intersections. But, of course, there won't be shared intersections in the usual sense. Instead, crossing FlyWays will be on different heights such that vehicles just pass above and below each other. Just like on grade-free highway crossings turning onto another FlyWay means merging out onto a ramp and then into the other main FlyWay. Therefore, the only traffic conflict possible in this system is two vehicles merging into one lane. And this is accomplished by an automatism which uses the kinetic energy of the vehicle which enters the merging zone last to speed up the vehicle which is ahead. The second vehicle will thereby lose speed such that the first one will clear the merging point safely ahead. Note that if the vehicle being slowed down is a train, then all the vehicles behind it will also be slowed down, while the vehicle being sped up is always pulled away from the train so that the other vehicle can sneak in. If two trains meet this results in vehicles being sped up from the front of the trains in alternation while the tails of the trains get slowed down more and more.

Flying Bicycles, so what?

Of course, this great invention of mine is not going to appear in reality very soon. I found one project, called Shweep, which is very similar to what I described here (they use a very narrow metal rail instead of the cable) and which itself is still in the research stages, especially for the switching technology: how to merge in and out of lanes. I admit that my description is very fuzzy in this regard and while the rest of the system is pretty low-tech and could have been build 50 or 100 years ago, the best solution for switching might actually use quite a bit of high-tech.

While doing research into this topic I found a lot of information about "Personal Rapid Transit" (PRT) systems, a combination of mass transit and private vehicles (basically a transit system that never requires transfers and always takes you from your starting station directly to the destination station). Despite much research this never took off big and the above-mentioned ULTra system at Heathrow airport is probably the example which handles the most traffic. ULTra with its vehicles driving on normal asphalt also shows that PRT now becomes less like rail-based systems and more like ordinary cars. To me, it actually seems quite likely that self-driving cars will popularize enabling driverless taxis and thereby fulfill all of PRTs promises plus picking people up at their door without the need of any stations at all! Isn't it fun to think that SciFi also imagined flying cars which were driven by people, but now in reality we seem to be getting the boring old combustion-powered asphalt-rolling cars, but they will drive themselves?! (I know that burning fuel to drive might get out of fashion soon with electric cars, but that's not a point I want to argue here. Besides: (1) electric traction (in street-cars) was commonplace in big cities many years before cars arrived at the scene, so it's not really a new technology, and (2) there are ways to produce engine fuel from other than crude oil, so maybe combustion engines will stay with us for longer than it seems now. See XtL (sorry German), English: CtL, BtL.)

Driverless cabs might make commutes much more relaxed and save a little space on crowed streets (for example, by separating the car into two compartments and taking two passengers on the same ride, or by taking a full four or more, for a cheaper rate than a bus and still end-to-end, with a minimal detour to drop off or pick up others), but they will not make obsolete the need to create higher capacity for transport in general as in new subway construction. The FlyWay, on the other hand, can take between 10% and 30% of inner city traffic which in itself might be just enough to considerably reduce congestion on the streets as well as in subways and buses. So the FlyWay isn't just a very relaxed, comfortable, and quick way to travel for those who use it, but it's also a great service to everybody else on the road.


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