
A company called SkyTran is making maglev passenger “cars” - ColinWright
http://secondnexus.com/technology-and-innovation/the-future-of-transportation/
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kragen
Background on skyTran is at
[https://en.wikipedia.org/wiki/SkyTran](https://en.wikipedia.org/wiki/SkyTran),
and on the general field of personal-rapid-transit systems in general at
[http://www.skytran.com/prt/](http://www.skytran.com/prt/).

Something like skyTran is going to be super important for future cities. A
regular gasoline-engine car can go 150 km/h, but in our cities they spend half
of their time stopped, and so it's common to get 15 km/h in real life. And
then you have to find a place to park it! Traditional massive subways and
elevated trains are better, but building them is too expensive to space them
closely — so unless you're lucky, you have to spend 20 minutes or more walking
to and from them. And then they still have to stop every 400 meters or so,
because you're sharing the car with other people. So you still end up
averaging something like 15 km/h.

A personal rapid transit system like skyTran can have lines spaced very
closely — as closely as streets, or more closely — and can _actually deliver_
close to its peak speed of 100 km/h. You could get from any place in San
Francisco to any other place in under ten minutes, instead of the hour-plus it
often takes at present.

How important is that? The entire benefit of a city is that you're close to
many people doing many things. It's being close to people that makes us put up
with the pollution, noise, and undesired social interaction that come with
cities. But with our current city transport systems, you're within 20 minutes
of only about 80 square kilometers, about half a million people. A system like
skyTran effectively brings you much closer: you would have 3500 square
kilometers within that same distance, about 25 million people, if density
didn't change.

That is, with skyTran or similar personal rapid transit systems, you could
live in a place that looks like San Mateo or Redwood City, except without the
cars — but enjoy _even more convenient access to_ city amenities like good
jobs, artisanal toast, live music, and offbeat special interest groups like
Postgres, than you can get today by living in the heart of San Francisco.

There's a critical mass needed to get benefits like this, and I suspect it's
close to the half-million people I mentioned above: on the order of a couple
hundred kilometers of transport line, densely covering an area of several tens
of square kilometers: an up-front investment on the order of a billion
dollars. But maybe skyTran's Tel Aviv project will surprise me and transform
Tel Aviv more than I expect.

In
[https://news.ycombinator.com/item?id=9788092](https://news.ycombinator.com/item?id=9788092)
I did the calculations to show that you could get substantial benefits by
replacing even the elevators in a single skyscraper with a skyTran-like
system. The numbers only get better as the system gets bigger. Scaling, far
from being a problem, is the solution. Eventually you will run into bisection
bandwidth problems, but only at scales far, far larger than our current
cities. A SkyTran track transports pairs of people at about 3Hz; 200 parallel
SkyTran tracks across the width of San Francisco could transport SF's entire
population from one side of the city to the other in 22 minutes (plus the
transit time of 6 minutes), or 11 minutes if they shared cars.

~~~
jakobegger
I'm not sure you're scaling logic checks out. You claim that a single track
can transport 3 cars per second. That sounds dangerous. Cars going 100km/h,
with a distance of roughly 5m... that will only be possible on long, straight
stretches. But conventional trains already work very well on long, straight
stretches.

The difficult thing about scaling something like SkyTran will be transferring
between tracks and merging at high-speed.

But even if all of that works nicely, you're still limited by the time people
take to get in and out of their cars. You'll end up with traffic jams waiting
for 20 people to get out of their cars before your car can park at the
station...

~~~
kragen
All of your criticisms seem ill-founded.

The actual number SkyTran is designed for is 3.2 cars per second, but I
rounded down for ease of calculation. That gives you 9 meters between the
fronts of cars, not 5. It turns out that when you can decelerate at human-
body-safe 6 gees, which you can do on a SkyTran track but not a regular
railroad track or street, then you can stop from 100 km/h in 6.6 meters.

As I've explained above, although conventional trains do work on long,
straight stretches, they do not in fact work very well for short-range trips,
delivering end-user speeds an order of magnitude lower than their peak speeds.
Even that they can only deliver at the cost of enormously expensive
infrastructure to support the massive cars needed to make conventional trains
cost-effective.

Long, straight stretches are not necessary for SkyTran; you can go just as
fast around curves as you can on straightaways, because the cars are suspended
from the tracks. Some other PRT systems do not have this advantage. You need
to keep acceleration loads manageable, but that's not difficult.

Merging at high speed is a trivial problem with a centralized real-time
control system. If you can ensure that cars on the same track are at given
relative positions to each other, then you can just as easily ensure that for
cars on different tracks that are going to merge to gether.

I'm not familiar enough with SkyTran's design for transferring between tracks
to know what problems you see with it. Can you elaborate?

If you had everyone going to (or from) the same station at the same time, you
_could_ have station traffic jams. (And I think SkyTran's per-car capacity of
2 passengers is probably suboptimal for this reason, among others.) But since
the stations are all on sidings, that only happens if you're going to the same
station and there isn't a siding free at that station. You can solve this
problem by going to another station nearby — I think the station spacing for
most places would ideally be around 50 meters, but if that isn't enough for
high-traffic areas, you could build stations there every 25, 10, or even 5
meters, thus further shortening the walk in the average case while removing
the bandwidth bottleneck in the overload case.

------
brudgers
Wikipedia on SkyTran:
[https://en.wikipedia.org/wiki/SkyTran](https://en.wikipedia.org/wiki/SkyTran)

~~~
biot
Not to be confused with SkyTrain:
[https://en.wikipedia.org/wiki/SkyTrain_(Vancouver)](https://en.wikipedia.org/wiki/SkyTrain_\(Vancouver\))

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nickhalfasleep
Part of the appeal of technology like this is that it capitalizes on one of
the few empty volumes of space in already crowded cities. Underground is
limited by existing infrastructure, the city streets are packed, so take from
the airspace in between buildings.

------
beautifulfreak
[http://paleofuture.com/blog/2007/5/24/closer-than-we-
think-m...](http://paleofuture.com/blog/2007/5/24/closer-than-we-think-
monoline-express-1961.html)

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jonsen
If the cabin is hinged, allowing for lateral movements caused by centrifugal
forces, it could go pretty fast through relatively short radius curves.

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3stripe
We already have "an efficient, sustainable and safe form of transportation" \-
and it's also both fun and healthy - the bicycle.

~~~
nine_k
Works well when the destination has a shower facility, or you don't mind
moving slowly.

~~~
arm
Or get an e-bike.

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jonsen
Why not use this for long distance? Wouldn't it result in cheaper "railway"
construction?

~~~
wongarsu
$8 million per kilometer is about the same price as regular railway, so this
sounds like a good alternative.

Maglev trains in general seem like great, cost efficient technology. They are
generally opted against because they require a different type of rails. Given
all the other high-speed train options, building a second rail network is
nearly never worth it.

This leaves only inner-city transportation to maglev, where there are no
shared rail tracks, and where maglev can shine with near-silent operation.

I don't really see how smaller train cars change any of this. You could build
one-person train cars on regular train tracks. You would have to upgrade all
the collision-prevention systems used by regular trains, but that's already
being worked on to allow better track utilization.

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mkj
I can't see what kind of people/hour figures they're expecting, anyone seen
that?

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toothrot
These would get so messy so fast in NYC.

