how universal is transit’s geometry?

240px-Uranus2 Suppose that somewhere else in our universe, there’s another planet with intelligent life.  We don’t know what they look like, or what gases they breathe, or what they eat, or whether they’re inches or miles tall.  We don’t know whether they move by hopping, drifting, or slithering.  We don’t even know if their lived environment is largely two-dimensional, like the surface of the earth, or freely three dimensional, perhaps a cloud-city full of cloud-beings who drift up and down as easily as they drift left or right.  We don’t know what they call themselves, so let’s call them borts.

Let’s make just two assumptions about them.

Let’s assume (1) that the borts tend to form large assemblages, which enable trade, creativity, ritual, and whatever other activities give value to their lives.  Let’s call these places cities.  Since cities are places where borts are relatively close together, it follows that they have relatively little space per bort.  Cities, by definition, are places where space is experienced as scarce.

Assume (2) that these cities are large enough that a bort can’t easily hop, drift, or slither around the city fast enough to reach all the needs and pleasures of daily life.  Given this reality, they must have invented vehicles of some kind that carry them faster and further; if they hadn’t, their cities could not have grown so large.

Do we have to make an assumption about their communications?  If the borts had either perfect telepathy or perfect virtual reality, then they would never need to move for any of the purposes of interaction.  But in this case, why would they have cities?  Let’s assume [and I think this arises from (2)] that their communications are not so perfect, and that they do need to move around to do whatever borts do that constitutes their lives and economies.

Perhaps the borts have tried using a personal locomotion vehicle in their cities.  It gives a bort freedom to move at high speeds, but it’s much bigger than the bort’s body, so it takes a lot of space inside the city.  Given the city’s limits on space, these vehicles – which require a lot of space per bort – would have collided with those limits, causing something like congestion.

So (regardless of whether they’ve tried the personal vehicle) they must have invented a vehicle that can carry many borts at once for travel within their cities — not to mention between them.  Call it a bortmover.

But then comes the “network design” challenge: in a city where borts need to move around freely, from anywhere to anywhere else, what exactly should the bortmovers do?  In what patterns should they move?

Well, they need to move in a known pattern, so that borts can predict them.  That means some kind of routing and schedule, and a schedule implies both a frequency and a span of service.  Borts need to get places soon, so that means that these vehicles must stop close to desired points of origin and destination, they must not require too much waiting, and they must be reasonably direct and also move at an adequate average speed.

So with only two basic assumptions about bort civilization, we can infer that they have concepts of stop spacing, frequency, span, directness, and speed.

Obviously, we can’t know what bortmovers cost to operate, but like all planets, the bort world is finite, so bort society must have a concept of scarcity.  Even if bortmovers cost nothing to run, there is still that defining scarcity of all cities: the relative shortage of space per bort.  Most likely there are other costs as well, reflecting the energy required to manufacture and operate the bortmover.  So there’s some limit to the number of bortmovers, which motivates borts to use them efficiently.

Presumably, some parts of the city have a greater density of bort activity than others, so even if a bort’s likelihood of boarding a bortmover is constant regardless of location, there’s more bortmover ridership in these denser areas.  So the borts experience a relationship between transit and density: if there are more borts within slithering/hopping/drifting distance of a bortmover stop, that’s a larger potential market, which means a busier bortmover.

So bortmover companies have to decide whether to route their bortmovers to maximize their ridership – which would mean no service to some of the more sparsely populated parts of the bort city – or to spread bortmover service across the whole city even though they’ll be crowded in some areas and lightly used in others.  They’ve faced the choice between planning for ridership and planning for coverage.

They’ve also discovered that if they try to run a direct bortmover from every part of the city to every other, they get poor frequency and high complexity.  Maybe the borts are all geniuses who love keeping complex networks in their minds, but poor frequency will still be an obstacle to getting where they’re going.  So borts must have discovered the connection.  That means they’ve faced a choice between connective networks (which are simple and frequent) and direct-service networks (which are complex and infrequent).  And if they’ve tried to optimize a truly connective network, they’ve probably discovered the grid, regardless of whether their cities are grid-shaped.

Again, because space is scarce, they probably experience something like congestion.  This problem will be worst where there are the most borts coming and going, but that’s exactly where the bortmovers are needed most, in high volume and with high quality.  So perhaps some of the busiest bortmovers have been given exclusive linear spaces that they can operate in, so that they can run fast and reliably.  Call them exclusive rights-of-way.

We don’t know much about the borts or their world, but with just two basic assumptions, we can infer that if they have invented transit, they have discovered the concepts of stop spacing, frequency, span, speed, directness, travel time, connections, and even right of way.

So bort transit must face the realities that we must face:  Closer stop spacing, for example, means slower speed.  Branching divides frequency. Straight lines are more likely to offer good travel time than winding ones, so the “be on the way” principle applies to bort communities as it does to ours.

In fact, almost all of the basic concepts of transit are realities of bort urban life, because they’re facts of  geometry.  They are true of anything we would recognize as transit, everywhere in the universe.  They are not negotiable.  So they should be the basis of our thinking about transit in cities, not a detail that can be left to the engineers.  Cities must respond to the intrinsic geometry of transit, just as suburbia has responded to the intrinsic geometry of roads.  And yes, you can use a cute, fun, or exciting transit vehicle, but that doesn’t change any of these geometric facts.  If you don’t understand transit’s geometry, technology won’t save you.

Updated 18 Nov 2011.

18 Responses to how universal is transit’s geometry?

  1. ant6n March 2, 2011 at 5:10 am #

    Lots of assumptions.
    (quot freely:)
    Take a second intelligent species on earth, the dolphins. We humans think we’re the smartest on earth, because we have digital watches, and they just play and bounce around in the water. They think they’re the smartest, for exactly the same reason.

  2. Beta Magellan March 2, 2011 at 6:41 am #

    Although I’m always tempted to go full Lem on debates about alien intelligence, Jarrett set his two axioms at the beginning, nice and clearly, which not only has the advatange of stifling our flights of fancy but also, rhetorically, reinforces the point about transit’s geometric restraints. Analogously to mathematics, if you start with a few assumption’s, you can build a system which follows certain rules. So, I’d say the basic approach—having “transit axioms” and building on them—serves your argument nicely, but I’m glad to see particular example was dropped—the borts seem a bit like a distraction, and even after stating your starting conditions I found myself wondering what a *truly* alien transit system would look like. 🙂
    Incidentally, my background’s in the earth sciences, so I try to keep up with what’s going on around the solar system as well; over the past month or so the planetary exploration blogosphere’s been discussing the possibility of sending affordable missions to the outer solar system, so imagine my surprise to see a picture of Uranus in Google Reader and then discover I’m reading Human Transit! Strange how I’m attracted to subjects with multi-decade timelines and are easily derailed by budget issues…

  3. Anon256 March 2, 2011 at 7:29 am #

    Sticking to your first two assumptions:
    – If Borts could move freely in three dimensions, I’m not convinced congestion from private vehicles would be such an issue, with the additional degrees of freedom for vehicles to move past each other.
    – Private vehicles driven by a cooperative system with faster-than-human reactions would also have far fewer congestion conflicts, and could join together to share a route rather than getting in each other’s way.
    – Borts with perfect “virtual reality”/online communication, or teleportation devices might still live together in cities in order to keep latency times as low as possible. This sort of desire leads human finance companies to build their servers relatively close together (to get the absolute most up-to-date market info), but space taken by the fiber optic cables connecting these servers is small and has almost never been a limiting factor.
    – Borts might be much less individualistic. It can take a long time for an ant to walk from one side of a large ant colony to another, but it rarely matters because another ant is already there.
    – Your dismissal of “flexible routes” seems especially weak. With a sufficient understanding of supply/demand or ant-like perception of common good, Bortmovers could be dispatched to run directly between whatever pair of points would happen to serve the most Borts at the current time. There would be no fixed schedule or route; either Borts would be able to predict where and when to catch Bortmovers by their own perception of demand, or they might be happy to wait/’walk’ while the greater number of Borts is served.
    – If for example Borts or Bortmovers propagated through electromagnetic waves rather than physical matter, they’d still have issues with congestion of the electromagnetic spectrum, requiring something like dedicated rights of way (just as we dedicate sections of spectrum to different uses). But ideas like “stop spacing” and “branching divides frequency” would seem meaningless in such a model.
    Really it seems to me that frequent transit only makes sense in a pretty narrow part of the space of all possible worlds. If moving in vehicles were a bit easier, the benefits of private vehicles would outweigh the cost, like packets on the internet or even (sometimes) bicycles. If moving in vehicles were a bit more difficult, a frequent transit network would become too congested and cities would be limited in size or heavily dependent on telecommunication. It’s hard to quantify the size/”likelihood” of the middle area of transit feasibility compared to these two extremes, but it’s definitely not universal. The above are just a few ideas of how a civilisation might satisfy your assumptions and still look very different from what you’ve imagined; I have no doubt that a real alien civilisation would seem stranger still.

  4. Peter Laws March 2, 2011 at 8:10 am #

    Bortsh*t. 🙂
    We know nothing of the Bort’s feelings about things like time and personal space.
    Maybe time is not important to your average, working-class Bort so being able to predict when the next Bortmover is due isn’t a big issue and if it’s a circuitous route they don’t care because they all enjoy the ride.
    Or maybe it is and Borts are all tied to some subliminal rhythm so that they naturally prefer things to happen on a regular beat, say every Bortspan or deciBortspan.
    Likewise, we don’t know how interpersonal relations are between Borts. Maybe they like being packed into Bortmovers to get where they are going.
    Or maybe they don’t, and while they enjoy the company of their fellow Borts, they don’t actually like to be within scent range of them.
    IOW, what you’ve described sounds a lot like Terra and how Terrans react to their environment.

  5. T0wnp1ann3r March 2, 2011 at 8:34 am #

    “…odd shiny things in the discard pile…”
    While the use of mythical aliens might not be appropriate to the book, the analysis is.
    And this is a good example of what makes for a good practical book, the way that Jane Jacobs analyzed how the city really works in “Death and Life…”
    Stripping away the glitzy posters and politicians’ speeches and master theories, just dealing with how things actually work, is important. Sadly, there are way too many books stating how things “should” be according to the author, and not enough that further the depth of knowledge of actually existing sitatuations.
    So definitely keep that focus in the book.

  6. Brian March 2, 2011 at 10:49 am #

    I don’t know how universal transit is at all. Remember that in the ancient world (before railroads) cities could grow up to one million denizens or more and none of them had mass transit outside of large boats.
    London, Peking, Angkor, Paris, and Tenochititlan grew into giant metropolises utterly dependent on walking as a form of transportation. We might want to compare the just-so story in this post with the reality of horses and boats in cities before transit.
    Tenochititlan had half a million citizens in 1500, probably the largest city in the world, and didn’t even have horses, though water transit on gondolas was common. After the smallpox epidemic of 1521 it took four centuries for that city to once again be the most populous on the planet but by that time it had a world class metro.
    Anyway, it’s easy to imagine a 3-D city that has millions and millions without needing transit, so long as all the residents can float or fly. Everything could just be very close together.
    Alternatively, routes and stop spacing and the like could be irrelevent in a city with demand-based transit called to wherever a resident is waiting which delivers him wherever he is going like a fleet of taxicabs with computerized prediction and universal smart-phones to ensure availability and efficiency. With the right technology we could build that system now and everyone would get to destinations faster in medium sized cities.
    So in both the ancient world and the future, maybe we can imagine things less constrained than in this essay.

  7. EngineerScotty March 2, 2011 at 10:49 am #

    Perhaps there are two colors of Borts, red and blue; with a high percentage of Red borts holding the Blue variety in contempt, and are generally unwilling to share a confined public space with them.
    Sucks how culture always manages to mess up geometry…

  8. Morgan Wick March 2, 2011 at 1:25 pm #

    I don’t think a third dimension would change the analysis much. Borts would probably still have to move in dedicated spaces between the places where they live and work. Perhaps their cities are a “series of tubes”. 🙂
    “Private vehicles driven by a cooperative system with faster-than-human reactions would also have far fewer congestion conflicts”: Only if by “faster-than-human” you mean “instantaneous”. Any reaction time delay will have some impact on congestion.

  9. anonymouse March 2, 2011 at 1:46 pm #

    Since someone brought up packets on the internet, I’d like to point out that congestion is a potentially huge problem there, and that the internet actually only works at all because everyone connected to it, down at the individual level, has agreed to restrain themselves to avoid congestion. Back in the 1980s, once computers and local networks got reasonably fast, it became possible to send lots of data quickly, and the internet of the time suffered from “congestion collapse”, where connections became so congested that their effective capacity to deliver the data that was needed (what the networking people call “goodput”) fell by three orders of magnitude. The solution was the TCP congestion control algorithm, which relies on client machines to detect congestion and slow down their rate of transmission in response. It basically relies on everyone cooperating for the greater good, because if you don’t cooperate, everyone loses.

  10. Jarrett March 2, 2011 at 2:12 pm #

    Brian. The pre-modern “metropolises” that you cite wouldn’t seem huge to us now. Paris within the old city walls was under a 30-minute walk from one side to the other, which is on the outer edge of acceptable travel time if you’ll be making lots of trips per day. These metropolises were also hierarchical societies where a fairly small number of important people had access to the powers of others for their travel around the city.
    I should have added a third assumption, namely that bort society is relatively egalitarian, such that a large share of borts need mobility around the city. That may be necessary to arrive at the likelihood that they have significant congestion — although of course the compact medieval city was so dense that it had pedestrian congestion.

  11. Alon Levy March 2, 2011 at 4:05 pm #

    Jarrett, even if the borts are relatively humanoid, there are lots of less obvious questions influencing urban development in their society:
    1. Which resources are available?
    2. What is the state of path-dependent technologies? (Surprisingly many things today depend on crazy WW2- and Cold War-era arms races). At a minimum, is metallurgy good enough for steam engines and their derivatives?
    3. How easy is it to grow and transport food for the borts?
    4. How sensitive are the borts to various forms of pollution and to various diseases?
    5. Does the bort social organization favor what we humans think are organic cities, or does it favor the clannish cul-de-sacs common in modern American suburbia and in some medieval Arab cities?
    6. How much is bort psychology affected by enclosed spaces, elevated structures, etc.? Do they have the same reactions to elevated freeways as humans?
    7. How does bort psychology construe safety? Does it have the same cultural theory of risk as humans, the same reaction to fatality rates of cars vs. planes, the same reaction to crime, etc.?
    8. Does bort society have the same urban-rural social issues as most industrial human societies?

  12. Matt T March 2, 2011 at 5:07 pm #

    I’ve met these Borts. They actually have a very efficient postal system, and their ability to fold themselves up from their amorphous blobs into something akin to an aerogramme is legendary. It costs only two Jarretts to post themselves airmail from anywhere to anywhere on their home planet, and riding in the postal tubes is fun, so life is grand and they wouldn’t have it any other way. They however are like most humans, in that they refuse to ride in buses.

  13. GMichaud March 2, 2011 at 8:23 pm #

    Or maybe the borts prefer a natural environment, with horses, coaches, keeping main cities walkable, with some electric trolleys and trains.
    The borts use the relationship of agriculture and the city to shape their transit. So like early St. Louis, (19th century)and in many traditionally designed cities they established market gardens ringing the city
    The borts made a conscious decision to avoid confinement operations for animals and emphasized local foods, which in turn influenced their physical planning as well as transportation planning,(distances, frequency, connections and so on)
    The borts had a big advantage in that they read the “The History of Earth” before they started building.

  14. Dave March 2, 2011 at 10:08 pm #

    Clever! And instructive. Maybe it should be in the book if only in the appendix so readers can use it to explain the realities of geometry to those less familiar with transit issues.

  15. Scott March 4, 2011 at 4:38 pm #

    “If the borts had either perfect telepathy or perfect virtual reality, then they would never need to move for any of the purposes of interaction. But in this case, why would they have cities?”
    One reason: Reproduction.
    I can’t think of its title at the moment, but there is an older piece of science fiction regarding the Far Far Future that addresses just this issue. In the story, most human beings live their entire lives in small, automated cells that provide for all their physical needs. They communicate through view screens. The one time they leave their pods is to travel – by dirigible, mind you! – when assigned by The Computer That Makes All Such Decisions to meet a scientifically selected partner for reproduction. Everything else is done by automation (until, of course, the automation breaks down…but that is a different topic). Now, I suppose you could also automate the transfer of reproductive material, but in any case the major question in such a society is not one of mass transportation of beings, but rather mass transportation of materials.

  16. Jarrett at March 4, 2011 at 4:45 pm #

    Scott.  Well, yes, but your scenario is close to saying that the borts are basically intelligent plants.  Even our world's dumb plants have, in the vastness of time, devised numerous clever ways to reproduce without moving.  But plants don't form cities! 

  17. Rob March 4, 2011 at 10:42 pm #

    So maybe they can slither onto a series of conveyor belts, where the outer belts move slowly for slitherers entering and existing, and the inner belts move faster for those going longer distances. Or maybe they can flow through fluid, or electricity, or they have pink tubes attached to vacuum cleaners that suck them from place to place. Or maybe they have a network of guideways that allow a personal pod vehicle to get from point to point directly (requiring some network intelligence).
    Or (and I know this is hard to imaging) maybe they have a system of exchange that allows them to set prices to balance supply and demand for space and other precious resources, and they use it to ration access of personal mobility devices to rights of way to avoid congestion.
    Probably not teleporting though. Imagine the security bureaucracy that would be needed to keep people from teleporting into your bedroom, or from teleporting your alien Tivo into their living room?

  18. Anon256 March 6, 2011 at 2:09 pm #

    @Rob: The fact that a technology would be difficult to regulate has never prevented one from being invented. (Though most scientifically conceivable teleportation technologies would require a physical device on both the sending and receiving ends.)