Are Magnetically Levitating 'Sky Pods' the Future of Travel?

September 23, 2009 by Miranda Marquit weblog

( -- As a society, we are increasingly interested in finding new ways of transportation that are cleaner for the environment. New concepts in mass transit seem to be one of the main ways to move toward this future. However, many people (especially in the U.S.) don't want to give up the privacy of individual travel. As a result, it might be that so-called "sky pods" may provide the answer.

A company in California, called Unimodal Systems, has designed a that allows individualized travel, but that is also a form of mass transit. The key lies in the use of "sky pods" that magnetically levitate from their rails. Discover Magazine reports on how the concept would work:

A passenger would enter a pod, type in where he or she wants to go, and the computer system would do the navigating (and driving). The pods would carry up to three people and travel up to 150 mph. The system would be computerized to deploy the pods to crowded areas, and smart enough to re-route to avoid .

The idea is to eventually reduce the reliance our society has on cars. The system could at first work in airports and crowded downtown urban areas. From there, Unimodal wants to expand systems that would be able to provide transportation on a wider basis.

The name of the system is SkyTran, and it does have the potential to reduce traffic and some of the problems, including , that come with it. Unimodal's web site also claims that systems are inexpensive, and can be built quickly and with only a small amount of the cost that goes into building freeways. And the kicker? The company claims that SkyTran can work using technology we already have.

Unimodal has been trying to get this project really moving over the better part of two years. Things seem to be making progress now that transportation is getting a little more focus, and now that the company has a contract with NASA's Ames Research Center. Unimodal will work on helping NASA to understand how use control software to enhance its activities in space and aeronautics. In return, SkyTran can get the resources it needs to develop into a viable form of urban transport. The vehicle is on display at the Ames Research Park.

While there is rarely anything that can be considered a truly perfect solution, Unimodal seems to think that SkyTran comes pretty close. Even if SkyTran only fulfills a portion of its promises, however, it is still worth looking into. After all, one of our biggest problems in transportation has been a reliance on outdated technology from the last century. Maybe its time to start looking into the technology of the 21st century.

© 2009

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3.8 / 5 (4) Sep 23, 2009
What's next, Futurama suction tubes?

Fun idea, but do they realize the infrastructure this thing would require? You'd have to not only build electromagnetic track over every single road there is, you'd have to do it 30ft in the air for some reason. Why suspend it? I assume since these things will go 150mph they aren't really meant for shuttling around cities, but rather to replace roads altogether. So just give it a track on the ground like mini maglev trains. It doesn't have to be exactly like a scifi movie, people.
3 / 5 (2) Sep 23, 2009

This makes a lot more sense than these things, as it uses already existing roads and cars. And to preempt the comment about these being "greener" than automated cars, where do you think the electricity to power the entire road (the track it floats on) comes from?
4.5 / 5 (2) Sep 23, 2009
Where do you think the electricity to power the entire road (the track it floats on) comes from?

At a guess, solar power, wind power, wave power, thermal power, nuclear, and space-based microwave power.

In short, any green, renewable source imaginable. The core of the system is removing the need for each vehicle to take in its own fuel and generate its own power from that.
Sep 23, 2009
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3 / 5 (2) Sep 23, 2009
Presumably when operating in the city they could run slower than 150mph. Since they have a much smaller footprint than cars, are faster, and are presumably more efficient about routing and traffic control fewer roads would be required, so the infrastructure would be substantially less expensive to build and much cheaper to maintain (in the north snow removal and pothole patching is a significant cost).

I'd suppose that the suspended depiction isn't the only possibility. However, in the city it is useful because it reduces the footprint required for transportation infrastructure, leaving the ground open for pedestrian and human-powered vehicle use. In the country the suspended design would be quite useful for eliminating the problem of the disruption of animal habitats (roads make it very difficult for a wide variety of animals to maintain their range).

I like the idea. Would love to see a proof of concept construction.
not rated yet Sep 23, 2009
The PRT concept does not call for guideway on every street. The ideal is to have stations every half mile, for a maximum station ridershed of a quarter mile. As much guideway as it would to take to link stations together is all that would be needed, at minimum.

Also, urban speeds would only need to be 25-40 mph. This is pretty standard in the PRT field (ULTra, Vectus, 2getthere, Taxi 2000, etc.)
5 / 5 (1) Sep 23, 2009
BTW, it _does_ have to be grade separated in some way. It makes things much easier in terms of automated control, and the goal is for streets to be for peds, pets and bikes. Elevated structure is more expensive the bigger the structure being put up and objects being transported.
1 / 5 (1) Sep 23, 2009
It would also avoid disruption of service from HITTING the animals, especially in areas with large deer populations. Here in eastern Kentucky the deer don't mind the roads at all. Many of them seem to be suicidal, judging from the time they spend standing in traffic. It certainly isn't reducing their population any!

These probably wouldn't be practical for rural service, because you'd have to have a track to every farmhouse. Intercity, maybe. In town, certainly, and 150 mph wouldn't be out of line in a large city. As an example, an cross-town express line from in New York or Tokyo could easily run that fast.
5 / 5 (1) Sep 23, 2009
I wonder about terminal transportation? In the city it wouldn't usually be a big problem to walk from the drop-off to the final destination, but if one is commuting to the suburbs it seems that there could be a substantial transport gap from the terminal to one's home, particularly if any cargo is being transported.

In good weather a quarter mile or so walk isn't bad, but I'm not sure I'd be terribly interested in the same walk in the not unusual 20F winter weather here. And it would be after sunset too.

In a fully transitioned system there might be protected walkways or bicycle paths, but it would take a long time to build out such infrastructure. Such issues might greatly reduce commuter ridership in some situations.
3.7 / 5 (3) Sep 23, 2009
Aw jeez, 1965 all over again. 'Somebody threw up in this one!' These rails would obtrude into every nice vista, worse than telepoles. Only worlds fairs would want them.
1 / 5 (2) Sep 23, 2009
Uhm... why not just upgrade the sub-ways? and make them unimodal so that you don't have to sit beside someone not your own smell (no offense but different cultures do have different degrees of tolerance when it comes to smell).
It invites to take on a different technology. but the only thing different here is the structure.
1 / 5 (1) Sep 23, 2009
"These probably wouldn't be practical for rural service, because you'd have to have a track to every farmhouse" Gee, ROADS go to every farm house. Farm houses even have DRIVEWAYS sometimes half a mile long. The roads have to be maintained and snow removed. Some how people built all those roads...
2.5 / 5 (2) Sep 24, 2009
As a concept this is nice but there are a a few problems from the art provided...
- One rail means when one car is loading/unloading the traffic behind is stopped. And the people in the last car have to stop and start several times. Hint: make the loading and unloading sections longer like a train station platform. So everyone can get on and off together.
- Magnetic levitation is way too close to passengers. Your mobile phone flies out of your pocket and is stuck to the ceiling of the car. Oh, yes your laptop as well. And say goodbye to your data.
- Individual mass transportation? Still crowded because your vehicle limits the number of people who can ride. One individual traveling alone takes up 4 seats because he takes one car by himself.

Fuel efficient computer controlled road vehicles that talk to a traffic grid and the vehicles around it are still a better solution that this.
3 / 5 (2) Sep 24, 2009
Super conductors and magnets are old hat.
What would be good would be helping to save animal habitats and allow only human powered vehicles on the surface. The huge argument revolves not around the technology but where to put it.
The cheapest and nastiest solution is to use current road infrastructure.
Helps no-one except the economic hacks in Government who would rather spend the money on a ten trillion dollar bomb instead.
Above or below ground are the other two scenarios.
Well, unless they are built from titanium and placed in tubes then as the global climate gets more intense the worse tornadoes, hurricanes, etc. which would destroy it above ground. What short sightedness. Also they would be an eyesore. The argument about scenic views versus traffic jams is ludicrous.We are talking essential services. Therefore the most logical place to place the tubes would be underground.This is the best way, but the dearest.Melbourne,Australia is the best example of useless public transport
5 / 5 (1) Sep 24, 2009
Ideas like this have existed for some time. The reason we, as americans experiencing and living in a culture, are becoming astute observers of the fact that as the economy shrinks, 'capital investment' will occur only by the government as private businesses cuttoff their investment levels, lower their expenses, wages, and employment rolls, in what will be a long and painful process of cutting costs to compete what everyone expects will be an extended recesion/depression for the people who most small non-luxury businesses rely upon as customers.

as government sponsored pork goes, i think this is appealing to me and to many other futurists as a 'cool' idea, but as a hardened cynic grounded in reality, we all know this is ridiculous. By that, i mean that there are so many things wrong with it beyond the actual practical reality of the getting the variabfor so many different reasons that this idea cannot ever be improved enough to 'ever' be made reasonably palatable for public investment
not rated yet Sep 24, 2009
This looks like a fine transitional technology and would whole-heartedly support it.

However, is it envisioned that cargo would still be shipped on roads, be on the same track, or a different track that has greater load capabilities?

It would be great to have bullet-trains for shipping mass quantities as well and only have semis for transport within a city or out to rural areas.

For travelling to areas where one of these terminals is not set up, rental electric scooters/cars could fill the gap.
1 / 5 (1) Sep 24, 2009
@LeftyTheLegend @Arikin
The proposal does not use superconductors or extraordinary strong magnets for active levitation. Instead it uses Inductrack for passive levitation. The movement of magnets arranged into Halbach arrays in the vehicle induce current into passive, unpowered wire loops in the track which creates a repulsive magnetic field. Above a threshold speed the magnetic force lifts the vehicle and allows it to coast.

The original small scale prototype had a lift-off speed of 22mph, but larger models could have much lower lift-off speeds.

Because the track does not include active components it should be reasonably inexpensive to produce.

The proposed cars carry up to 3 passengers to fit well with the normal urban transport patterns (usually 1, sometimes 2, rarely 3 or more). Also, nothing about the design precludes the addition of one and two passenger vehicles.
1 / 5 (1) Sep 24, 2009
SDMike: A farm road is much cheaper to build than a maglev guideway, and poses fewer engineering challenges. It doesn't have to worry about sharp curves, hills, etc. Many of the farm roads were originally built by the farmers and were suitable only for wagons. We've had 200 years to rebuild them for modern vehicles, and many are still barely suitable.

Trying to build a maglev track down every farm road would be prohibitively expensive, and we'd still need the roads for the freight.
2 / 5 (4) Sep 24, 2009
i was going to comment earlier...

now i have a momemnt..

it seems that their whole business model rests on their solution for the p np complete problem. :)

that is, with say 400 stops, and another 400 nodes, they could not compute routes for people and be able to reroute.

lets just say that the permutations are something like 400 times 399, times 398, etc adding nodes just adds more permutations.

this design is completely impractical

lets have a fun example ofwaht can go wrong.

child thinks its cool, throws a toy up in the air. the toy is slamed by a two ton vehicle at 150 miles an hour. like a home run baseball the toy comes off the machine, and hits people in the crowd.

birds will be creamed by these cars in the air.

and a terrorist would only need to run their car into one pole on a high speed track.

in a socialist communist world, this is not possible. in the world we were heading to before that, it might have been possibe.

5 / 5 (1) Sep 24, 2009
We've had 200 years to rebuild them for modern vehicles, and many are still barely suitable.

Trying to build a maglev track down every farm road would be prohibitively expensive, and we'd still need the roads for the freight.

We had modern vehicles 200 years ago?

As with everything else, you build the primary tracks first, then link extras in once the standards are established, slowly spiderwebbing out to smaller communities.
not rated yet Sep 24, 2009
@ pol:

Uhm... you wouldn't need PRT if there is already a subway system with the desired short intervals between stations.
not rated yet Sep 24, 2009
@ Arikin:

The concept calls for an empty pod to a) wait in the station until needed, b) reposition to empty berths in other stations, c) go to another station where there are no pods in response to a ride request, or d) do b) or when room needs to be made for arriving pods.

Other ways of dealing with it: In a really large system, 'surplus' pods could be put in a storage location during low traffic periods. Some designs use pods not locked to the guideway, meaning it is possible for vehicles to pass each other when in stations.

No congestion overall because the # pods in system is set, you would not have more than could be dealt with.
not rated yet Sep 24, 2009
@ ArtflDgr:

PRT designs use some variation of 'vehicle protection.' Basically how it works: the system designates moving blocks on the guideway representing slots for pods. Slots are not allowed to overlap.

Some designs envision slots that can change in size, others not. A network's control system knows where the pods are because there are sensors in the guideway, and the vehicles keep track too. So there are multiple position reports, and they must match in order for the system to be running. If they don't match the system sends a corrective instruction.

If it didn't work, podcars wouldn't have received regulatory approval in the UK and Sweden.
5 / 5 (1) Sep 24, 2009
re rural areas and farms:

Obviously PRT is not a panacea. No technology is suitable for all applications.
not rated yet Sep 24, 2009
@ oredson:
In fact, some PRT designs envision cargo versions. ATS (the Heathrow PRT) recently unveiled a pallette carrying vehicle,

Cybercab, to be used at Masdar City,
is to have passenger PRT, and freight "FRT" for cargo and recyclables,
not rated yet Sep 24, 2009
Some designs use pods not locked to the guideway, meaning it is possible for vehicles to pass each other when in stations.
Or people could de-pod at stations and walk to the front of the podline.
not rated yet Sep 24, 2009
@ otto1923:

Ah, I see the problem. The article did not explain that all PRT stations are on sidings. Pods destined for a particular station pull off the main line onto that station's siding. Pods not needing to stop at a station go right on by.

In the second illutration in the article, if you look closely you will see the lower guideway is labeled: "Extra vehicles waiting on the off line guideway."
not rated yet Sep 24, 2009
If anyone is interested in looking into SkyTran further, has tons of information. I'm a volunteer working on it.

@ArtflDgr - I wouldn't worry about the NP-complete problem. With a few heuristics, you can get pretty optimal in a millisecond. Internet backbone routers do this all the time.

@nkalanaga - you're right that building SkyTran on every road would be extremely expensive. This isn't the plan. In fact, SkyTran's goal is *not* to replace roads and cars. SkyTrans goal is to eliminate commuter congestion. Anything that is "on the way" to that goal is just added benefit.

If anyone wants to ask me questions here, I'll monitor this thread for a bit. Or if you want you can email me at bitetrudpublic at .
not rated yet Sep 24, 2009

I didn't see any cost projections on the website. How much do various parts of the system cost (pods, a track section, etc).

Is anyone working on or are there plans for a demonstration installation?

How do track junctions work?
1 / 5 (3) Sep 25, 2009
@ArtflDgr - I wouldn't worry about the NP-complete problem. With a few heuristics, you can get pretty optimal in a millisecond. Internet backbone routers do this all the time.

actually they dont... they cut up your car, put it in pieces and throws it out there... it does NOT use routing maps and such.

again, this is an intractable problem.
ESPECIALLY when one can go point to point from any point.

@mr grant... i think you were talking to someone else as i never said you couldnt run a train system by computer. what i am saying is you cant run a point to point system where a car can go anywher within the system.

there are SOOOO many problems its not funny.
way too many... and the problems have little to do with whether some small part is functional or not.

if its like the ny subway, people may get stuck for 24 hours cause of a swtich failure. power failures would lead to what? how would people get out?
1 / 5 (1) Sep 25, 2009
@ "cant run a point to point system where a car can go anywher within the system"
I'm curious to see an explanation of this.

@ "how would people get out?"
I'll ask you: what would your contingency plan be to deal with a power failure in PRT?
3 / 5 (2) Sep 25, 2009
Actually, the "NP Complete" issue isn't a real problem. True, the computer probably couldn't find the IDEAL route for every pod, but it wouldn't take much work to find a "reasonably good" one, and the time differences would be so small that most people wouldn't notice the difference.

Besides, humans run such systems every time they drive, and that's with less information than the computer would have.
5 / 5 (1) Sep 25, 2009
NP-complete isn't a problem in this system. While it does make it problematic to calculate the truly optimal route, it isn't necessary for the calculated routes to actually be optimal. They just have to be pretty good.

Power failure is addressed on the website. They have plans for backup system power. If that fails the pods have on-board batteries with which to propel themselves to the next off-ramp. If that fails they can be pushed to the off-ramp by the pod behind them.

I am still curious as to how cars switch tracks. I see that the pod support is intended to run inside a hollow track, but I'm curious about the details of this sort of track switching at high speed.

How much does crosswind loading on the pod affect the speed at which pods can successfully navigate a junction?

If the system power is down and pods are rolling rather than levitating do the junctions still work?

Are there mechanical lockouts on the track to prevent merge collisions?
5 / 5 (1) Sep 25, 2009

Cost estimates are something we still need to put up. Vehicles should be less than $3000 under mass production - officially we will say something on the order of between $5000 and $10k per vehicle before mass production (though I consider 10k a pretty high estimate). Guideway should be around 3 million per mile under mass production - officially we are saying $10 million per uni-directional mile and $15 million for bi-directional (again pre-mass-production). Stations I'm much less sure about, ballpark guess is $20,000. I used $10k in my paper on SkyTran in San Francisco (

By "track junctions" I assume you mean switches or places where a vehicle changes direction. Those are done magnetically, basically when a vehicle approches a fork, a magnet will push the vehicle either left or right.

As for demo and test for demo instalations, all I can say is we're working on it. I'm not sure how much else I can say (we're keeping on the down low for now).
not rated yet Sep 25, 2009
@ArtflDgr - If routing was intractable, how would a taxi driver ever be able to find your destination? I see other have addressed your question here.

"ny subway, people may get stuck for 24 hours cause of a swtich failure. power failures would lead to what? how would people get out?"

I see some of the others have answered these questions for you. To elaborate: we use magnetic switching - so failure is a few orders of magnitude less frequent than in subways; power failures would lead to vehicles coasting to the next station (electricity is not needed for levitation); vehicles have small backup batteries to power things like heating (in freezing weather), emergency brakes, and the door.


Just to clarify, back-up batteries probably won't be used to power the vehicle (since they'll coast without power and since the linear drive is in the track rather than in the vehicle).
not rated yet Sep 25, 2009

Magnets are strong, crosswinds any weaker than a hurricane shouldn't be a problem. As for junctions working during a power outage, the answer is: yes they'll have to work without track power, because it would be disastrous otherwise. However, this isn't a problem I've seen addressed, I'll bring this up with my group. My answer would be to arrange the junction so that vehicles would naturally take one of the two junctions (without any magnetic intervention). Ideally that default direction would be a turn off to a station. Alternatively, vehicles could be able to initiate changing direction (as opposed to the track).

"Are there mechanical lockouts on the track to prevent merge collisions?"

No. Vehicles have active radar and mechanical brakes to prevent such collisions.
not rated yet Sep 25, 2009
The magnets are strong, but with the mechanical advantage from the tall pods working against the narrow gauge of the track you'll have an awful lot of torque on the magnets. Large maglev trains appear to have a much wider gauge, so less mechanical advantage and less force. I'm not saying it wouldn't work, just that it's the sort of thing that requires some engineering. Gusts to 70MPH aren't uncommon where I live, and the back of the envelop says that could result in sudden wind loads of 200kg or more at the magnets, potentially when the pod is switching tracks.

The idea of a junction needing to be powered to keep pods on the main track is neat. It results in fail-safe behavior of side-tracking everyone ASAP. Busy routes would stack up and strand people on the main guideway though. Lacking on-board power to propel the pod would mean that they'd have to sit around and wait for someone to rescue them.
not rated yet Sep 25, 2009
@ switch questions:

The best mechanical PRT switch design I've seen is set up so it has to be in either left or right mode, no in-between.

The late-70s Aerospace Corp. scale model seemed to function fine with electromagnetic switches.

5 / 5 (2) Sep 26, 2009
Oh cmon, just put GPS in cars, control them with computers on highways, switch to manual when you get to local, slower traffic. Europe will have this in a couple of years, no need for new infrastructure.
Cars will go electric, or in other way sustainable non-pollutable too, so no problem there either.
not rated yet Sep 26, 2009
@codesuidae - "an awful lot of torque on the magnets."

Vehicles have a hinged connection to the bogie in the track, so there won't be very much torque at all.

"Lacking on-board power ... they'd have to .. wait for someone to rescue them."

Yes. The situations where grid power and backup power fails and where vehicles are forced to make an emergency stop (losing their coating speed) would most likely mean there is a larger problem that can't be solved by putting a motor in the vehicles.

@EarthlingX - how will GPS and electric cars solve gridlock? I'm all for it, but reliable automated cars are decades if not centuries out, because of the unpredictability of the open road.
5 / 5 (1) Sep 26, 2009
Er, folks, there wasn't room in that pictured pod for a week's shopping, a pram, a baby-carrier, a suitcase or a non-standard sized person, never mind one of limited mobility or wielding a walking stick.

Even if I can shoe-horn arthritic Gran into a recumbent seat, where do I put the wheel-chair ??
3 / 5 (2) Sep 26, 2009
NP-complete isn't a problem in this system. While it does make it problematic to calculate the truly optimal route, it isn't necessary for the calculated routes to actually be optimal. They just have to be pretty good.

This problem is not NP-complete. It is a special case of linear programming called the assignment problem or the transportation problem. You want to assign people to destinations or cargoes to routes or whatever subject to capacity constraints. This special case can be solved in N cubed lg2(N) time for, in this case N pods in the system. But there is a special trick that allows it to be solved in N squared lg2(N) time. For say 10,000 cars the difference between 13,000,000,000,000 operations and 1,300,000,000 operations. Call it going from one quad-core CPU per pod, to one CPU to do the whole thing. But it is nastier than that. Partitioning the problem between CPUs takes N cubed ln2(N) time. So trying to distribute the solution doesn't work.
not rated yet Sep 27, 2009
I suggest a trial of this system be built to test its feasability. Some potential locations include Brockway, Ogdenville and North Haverbrook.
5 / 5 (1) Sep 27, 2009
A reference to the Simpson's monorail episode is the PRT equivalent of Godwin's Law
not rated yet Sep 27, 2009
I like to select what car a drive, and, where to park it, who to drop off and who to pickup. This SkyTran is nothing but buses on tracks, except you're alone, more like, it's a taxi on track.

Lets use the green energy to power our cars instead.

But again, it's all about money, it's never about us. We, the people, will have to pay, no matter what. They already have the technology to power our cars for months at a time, but that doesn't bring them any money does it.
not rated yet Sep 28, 2009
The computation question is a non issue. If it were, existing GPS navigation devices wouldn't work. They have many more routes with many more conditional weightings involved involved in their route planning. The proposed system is pretty uniform and would have several orders of magnitude fewer routes than existing roadways.
not rated yet Sep 28, 2009
@michaeloder - "several orders of magnitude fewer routes"

Actually, hopefully a PRT system would eventually have maybe 5 to 10 times fewer roadways (because of higher capacity). I assume you're thinking when its first built?
not rated yet Sep 28, 2009
@ Nik_2213:

You've identified one of the issues a lot of people have had with the SkyTran design -- by insisting it look irresistably cool, the ADA compliance has always been open to question. However, sources now tell me the current version at Ames looks the same, but is larger, can carry more than two people, and has a cargo compartment in the back.

Other PRT designs (see ULTra, Vectus, Cybercab, Taxi2000) are more obviously accessible, and have capacity to carry parcels and bikes.

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