In the far future, cities are spreading across continents, some cities are as large as france (~1000 km across) after smaller cities have grown together - Into Super Cities.

Now Marchettis Constant states that a city's limit in size is estimated one hour commuting.

  • How would public transportation and the roadways look if you need to move at an average of 1000km/h?
  • What kind of vehicle would you need to achieve that (Vacuumtube trains?, Flying cars?, Micro stargate'ish- Teleportation?)
  • Given any imaginary techonology, how could this be achieved ?
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    $\begingroup$ Marchettis constant does not directly apply to super cities. It has the implicit assumption that the distance between major cities is larger than the constant. In the super city scenario the gaps between cities have been filled. Essentially a super city and normal city compare like a multicellular organism and an amoeba do. The super city would be composed discrete districts each capable of all basic functions and of size limited by the constant. (Not going to expand as this is not what you are asking, just assumed you'd be interested.) $\endgroup$ May 20 '15 at 15:25
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    $\begingroup$ There's a reasonable chance that instead of actually commuting, virtual reality will take over a lot of the need to commute instead. Goods can be transported at low speed by machines, and if people want to get together they just fire up a virtual space and meet there. $\endgroup$
    – Erik
    May 20 '15 at 15:37
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    $\begingroup$ Don't forget that driverless (computer-controlled) cars—a technology that is in its infancy currently but will be the norm within a generation—and the decoupling of human attention (as well as risk of injury/delays due to accidents) from commute will also have a huge effect on this question. More than an hour's commute time per day is less of a concern if you can spend the time napping, working, gaming, or using the internet. And the more cars become driverless, the fewer accidents and traffic delays will slow cars, so commuters will be able to get a lot further per given unit of commute time. $\endgroup$ May 20 '15 at 17:39
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    $\begingroup$ This is the future, so why would most people even need to commute? Even a decade ago, I worked in both Europe and Silicon Valley while living in the US Great Basin. Also, think about how & where your megacity gets its food supply. $\endgroup$
    – jamesqf
    May 20 '15 at 18:24
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    $\begingroup$ Between driverless cars, telepresence/virtual reality, and other soon-to-be-real technologies, and the fact that people can live in high-density housing right in a city, I'd say the logistics of food importation will be more important to the upper bound on a megacity than commute times. Much of the Japanese islands already qualifies as megacities by American population-density standards. $\endgroup$ May 21 '15 at 1:38

First of all, let's clear up a fundamental misunderstanding: Marchetti's Constant does not state that a city's size is limited to one hour of commuting, but rather that people will adjust their routines such that they spend, on average, one hour commuting. This means it does not impose any restrictions on city size, it only supposes that people will live up to ~30 minutes from where they work (giving an average daily commute of 1 hour). In fact that's evident today already, where numerous cities take much more than an hour to commute from one side to the other (especially if you catch traffic at the wrong time!), though on average people live much closer than "the other side of the city" from where they work.

It does have implications on urban planning, though, such as implying that a residential zone without much work available in a 30-minute commute probably won't be much lived-in.

That said, the Supercities of the future are still likely to have very interesting modes of transport for when people do want to travel further than 30 minutes, and even for extending how far 30 minutes actually gets you:

Trains and Flying Cars

AndyD273 has already addressed these in his excellent answer. I'd just point out that China's 2010 1000kph train is no doubt slower than the express trains of the future, especially if vacuum tube trains become a reality. I'd also add that flying cars, barring some sort of hand-wavium that (at least partly) negates gravity, would necessarily be much more energy-intensive than surface-driving cars, meaning they'd never fully replace the latter.


The expressways of today are pretty much just wide boulevards with limited traffic lights so that you can drive from Point A to Point B more quickly. We're already on the cusp of the next generation, though: Expressways designed expressly for self-driving cars.

This would work in a way that blends high-speed trains with taxis: You would hail a car, get in, and it would take you to where you need to go. No having to bother with all that lane and signaling nonsense, either; advanced computer algorithms would dynamically adjust the paths of each individual car (in much the same way that air traffic controllers guide airplanes) so that each one has a clear path from Point A to Point B.

With expressways closed to any other vehicles, these computer-guided cars would be free to run just as fast as we can make their engines capable of, without fear of collisions; while unlikely to beat a high-speed train in a speed challenge, they would have an extraordinary advantage: There'd be no need to get out and transfer to a local leg, because your self-driving car could simply get off the expressway and -- albeit at a slower speed -- navigate surface streets to bring you directly to your destination! [NB: You'd probably put opaque windows in these things, at least while on the expressways, because your human passengers would very likely find themselves in a heightened state of anxiety if they can see the seemingly-chaotic mass of cars driving at high speeds through laneless roads, weaving between one another as they approach at deadly speeds head-on before veering off -- very often the most expedient path is not what we're used to seeing with our static concepts of "lanes" as "safe passing zones"!]

You could even physically separate the self-driving cars from everyone else by having them suspended underneath the expressways (a la the Total Recall reboot), freeing the surface to be available for manually-operated cars (if those even still exist...) or even high-speed trains.


This is already a thing today; I spent 6 years working from the office in my home for a company that would have otherwise required an 8-hour flight one way to get to their offices. That was your run-of-the-mill telecommuting though, where I'd be typing on my computer or talking on the phone all day; these days you can get yourself telepresence robots (link is just one example) to have a physical, mobile presence in an office on the other side of the globe, let alone one merely 800 km on the other side of the Supercity.

As these become more ubiquitous in office environments, commuting will become a lot less of a consideration.

In a very similar vein, MMO games have given us another option: The virtual office. After all, if you can get 25-50 people together for 8 hours to battle a pixelated dragon, certainly you could hold a 1-hour staff meeting in a similar manner? The advantage this has is that you can base your avatar on your own appearance, allowing others to still connect with you visually, and/or customize your avatar to your personal preferences (similar to the MMORPG character generators today), which has many of the same benefits (assuming you don't frequently change your appearance, that is). As VR systems improve, this is likely to become even more prevalent and more accepted.

After all, even today there's really no need for countless individuals to ever set foot in an office; as this becomes a more widely-accepted fact, and the various telepresence technologies provide comfort to the clingers-on of the "old ways", commuting will become more and more an artifact of a bygone era.

  • $\begingroup$ Hmm, I kind of forgot the self driving car thing... The (slight) problems I see with automotive transport in a mega city is that it would most likely be slowish (600mph is hard to do with a surface vehicle), and not being able to see out would probably cause motion sickness with all the weaving. Also the noise, and roads able to handle that many people take up so much space. There are probably ways to fix these problems, probably a mix of rail/automotive to cut down on the number of cars needed, and only really using cars if you need to move stuff that doesn't do well on a train. $\endgroup$
    – AndyD273
    May 20 '15 at 17:34
  • $\begingroup$ The noise is easy to handle with electric cars, or at least mitigate significantly -- I don't see it being any worse than today's highways. Good point on the motion sickness, though; perhaps replace the opaque windows with screens displaying what's outside after removing the other vehicles from the scene? $\endgroup$
    – Kromey
    May 20 '15 at 21:32
  • $\begingroup$ Just heard of this today: Honda proposes grid of accident-resistant, clean energy cars that go 180 mph. I agree that the noise wouldn't be any worse than what we have now, and probably better with electric cars. I'm just saying that what we currently have can be bad, noise wise. $\endgroup$
    – AndyD273
    May 21 '15 at 0:46
  • $\begingroup$ I never thought about the fact that an efficient network of self-driving cars would need opaque windows. More and more I'm realizing that the future is terrifying. $\endgroup$ May 21 '15 at 19:02
  • $\begingroup$ I think a mixed high-speed levitation trains adapted that can pick/drop people anywhere in the city works better...think about it you are at some street u pick your phone an call the 'taxi' and the nearest empty mini-trains come to you or you go somewhere to find them...mini-trains enter the train network and accelerate to 1500-2000km/h and drop you at home and cycle repeats... No need to wait slot no need to deal with millions of people confined in a train station's and if you design it well you can as well have a nice view above the city $\endgroup$
    – Freedo
    May 22 '15 at 1:47


Back in 2010 China was looking at making a 1000kph train. The problem with having a train like this in the mega city is the stops. You'd want to get it up to speed and then only stop when you got to the other side, but it would skip everything in the middle. If you were stopping a lot for passengers then you'd lose a lot of time/momentum. You'd have to have to have several layers of trains to make it work.

Local, to get around the neighborhoods, like a modern subway system. Maybe have a stop every couple blocks.
Short Range, to move between local groups faster than hopping from line to line.
Express, to travel from once side to the other very fast. This would be the 1000kph train.

Having the 1 hour commute be a hard limit would still keep the cities from being 1000 km across, since you'd have to travel from home --> local --> express --> local --> work... but it would be close.

Flying cars

As Frostfyre said, see Coruscant as an example of what this would look like...


This is probably the best possible way, as there would be no theoretical limit on how large your city could grow without you being able to get anywhere within a couple minutes.

An example is Niven's teleporation booths and stepping disks:

Earth uses teleportation booths to provide near instantaneous travel throughout the world, but the Puppeteers have created a series of stepping disks on their homeworld which allow them instant travel; they can walk the entirety of their homeworld in minutes, giving them "seven league boots". Unlike the booths, the stepping disks can be installed anywhere and are portable. Transfer booths, used for transport on Human worlds, are an inferior variant on the stepping disc, using technology secretly sold by the Puppeteers to one of Gregory Pelton's ancestors.


I would bet on mini-low capacity maglev trains as means of mass transportation...i was planning a story with mega cities like that so i've think about that. I'll cite my reasons.

  • In a mega city you got millions of people that want to go to different places and they want to get it here fast safely and comfortable (nobody likes the insane overcapacity trains/metros of today right?)

  • How would you concentrate insane amounts of people in a station to wait for trains or whatever? Nobody would like that and no matter how big and fast your tech are you will always have more people wanting to use it than you can provide.

    • Most of people are alone or in small groups.

That's why I think mini-low capacity maglev trains are better , they don't make any noise they don't pollute and in future they will probably go 2000km/h or more but as others have pointed the problem of centralized networks and stations are the stops you would never get to 2000km/h if you stop every 1km or less.

You could have 4 lanes of maglevs trains , one for near maximum speeds , one for 50% to 70% speed and one for low speed for short travel and one lane that is exclusively to stop and pick/drop people.

Make it connected so any maglev train can go to any lane if needed and let an AI handle the driving and optimization of the system. Make it low-capacity like 5 to 7 people so you don't gather a crowds waiting for it.

Built it so that any person can request an maglev train anywhere at anytime on city(i think suspended lanes above the ground will work the best) and if you want you can have the AI to pick people that are going very close to the end destination.

And forget cars they just don't work on big cities driverless or not they will never be a mean of fast mass transportation and they are messy chaotic and require lots of space to be built for them.


If you're happy to go more down the route of pre-planned megacity or to have a city-wide transportation upgrade programme then potentially something like a PRT network could be useful. The joy of an integrated, automated network is that you can then incorporate multiple different transport networks to efficiently route traffic across the city. This automation is the key component, as the problem with such a large city is not necessarily straight line distance, but is more likely to be traffic flow management. I spend most of my commute time waiting for trains that are late or stuck behind red lights when there are no other cars on the junction.

For example, Joe Bloggs orders a PRT pod for work. He gets in and directed the automated system to get him to work ASAP. The pod acknowledges, closes the doors and accelerates at a gentle pace. Route planning software is already tracking all other PRT modules, and decides the best way to get Joe to his workplace is to shuttle onto the nearby Heavy Rail Transit network, where a larger scale Maglev train with a dedicated PRT pod carriage (or two) is waiting. The HRT then takes Joe across the city (along with an efficiently packed number of other cars), his PRT pod completes the rest of the journey and Joe steps directly into his office.

On the journey home, however, the HRT network is not running in the same direction as Joe. The transit network analyses current traffic rates on all major thoroughfares, shunts Joe's pod onto one of the lower level, lower speed lines, handily routing him around the major blockage points caused by the evening rush. Halfway home Joe's pod unexpectedly veers into a siding station a few seconds before a medical transport rushes silently by. The medical transport continues at breakneck speed until it hits the airport, barely decelerates in time to come to rest in the cargo hold of a ramjet aircraft which immediately begins its takeoff run to deliver a still beating heart to the other side of the world for transplant. Meanwhile Joe arrives home and is greeted by his adoring LoveBot 5000

  • $\begingroup$ I just love this idea $\endgroup$ May 26 '15 at 15:00

Without getting into magical systems like teleporters, I would suggest that huge urban conglomerations like that would actually morph into more three dimensional structures similar to Arcologies.

As a three dimensional structure, everything is much closer at hand, and elaborate and expensive epress transportation systems are not really needed inside, but can be optimized to provide transportation between cities. As well, the Arcology, like a normal 2 dimensional city, would also be divided into neighbourhoods, where people would probably define their neighbourhood as the place where most of why they need day to day is available in a short walk or elevator ride (how far might be cultural or social, a "five minute walk" for a young man might be impossibly tedious for an 80 year old woman).

The resource bill for a "city" the size of France would be immense, and I suspect much of any "real" city like that would actually resemble a shantytown like those surrounding a third world megalopolis, with most of the people unable or unwilling to move very far from their cardboard and tin shacks.


What people want

People usually try to find equilibrium between two things:

  • They want to breath clean air, sleep undisturbed, have kids playing in the garden, not too expensive yet big house and with a nice view. This would be a remote countryside or a small village.

  • They want to be close to the office, facilities and social/cultural life, this would be a city centre.

Marchetti described the relation that exists between the two: 1 hour commute is the compromise. If you enhance the transportation speed, people are still going to live at 30 minutes from a place where things (work/museums/bars/shops/…) happens . So if you create a very efficient transportation system, it’s very likely that people are going to live even further to the place of work and keep commute 30 minutes.


If you go to the extreme and invent tele-transportation, or generalize remote office, people are not going to group into cities. I would go to a mountain, in an isolated woodhouse, and jump in my tele-transportation machine every time I want to go to work or to see my friends.

The territory will look like many isolated houses, small villages, isolated companies’ buildings (I have a cool company, our offices are at the north pole!). Maybe a pub street in the middle of nowhere, to go pub crawling without having to take the teleport machine between bars.

Your case

Now, your case. Even if, seen from space, your country looks like a big city, it will have many sub-systems, many “downtown” areas. These centres areas are going to be, according to Marchetti’s law, about 1hour commute time from each other (well, ok, this assumes that transportation speed is the same between centres than between suburb to centre, which is not true. It’s usually faster to go from one centre to the other than from the centre to the suburb, but let’s assume it).

So transportation is not as primordial as city planning. You can, if you want, keep the current transportation hardware and make a city of any size work fine, as long as it is well planned for this kind of transportation.


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