Saudi Crown Prince Mohammed bin Salman’s vision inspired by Miami.
Perhaps the world’s most audacious urban project is the proposed (and partly underway) 170km long city called “The Line” in the NEOM region of Saudi Arabia. They imagine a giant city, costing $1 trillion to build, holding 9 million people, and consisting of a massive structure, 200m wide and 500m high and … 170km long. The city would cut across the empty desert. It has already started.
This vision has seen a lot of criticism, some of it is valid, and it could not happen under other than an absolute ruler like Mohammed bin Salman, the controversial crown prince who is also head of this project. But rather than address those issues, the question is, “does it make sense to build a city as a line?” All other cities of course are 2-dimensional on the ground, even planned cities, and grow organically to fit their terrain in shapes that are roughly rectangular or circular.
The design is chosen because it allows their transit plan, including trains that run under the city, with a special high-speed train that will traverse the entire 170km in just 20 minutes, making it the fastest HSR in the world. To do that, that HSR will have only 4 stops. Other, lower-speed services will also run, including transport pods that run at high altitudes so people don’t have to go down to the ground level to access transit as they do in other skyscraper cities. Their plan is to build a “5-minute city” where you can get all the basics you need with just a 5-minute walk. It will also be a short walk to transit that takes you anywhere in your area or to the HSR to go to other parts of the Line.
The 5-minute city is a bold goal — most who aspire to this have settled on a 15-minute goal, as first stated in Paris. By making the city a line, they can serve it with one massive train line. In 2-dimensional cities, you often have to change trains, perhaps even twice to get between locations. Cars and bicycles can drive from A to B on a street grid but the Line will not have cars.
High-speed rail is the most difficult. The track must be extremely straight, and you can’t have too many stations. If the train has to stop often, it drops the real speed too much. This is the curse of traditional HSR, you have to put the line through the territory, disrupting the life of those who live or farm there, and those people are too far from a station to get much benefit. At least in the Line the train is underground and not disrupting life far from the stations.
The linear plan works only if you go big — large, fairly frequent trains. The distance between points is much larger than a traditional square city, so you need very high speed and few stops to provide short travel times. The line’s buildings plan to be 200m wide and facing inward — the outer walls are mirrored, though with windows for spaces on those outer walls. Those windows, onto nature, and the ability to be next to nature (though in this case a beautiful but inhospitable desert) are a virtue of this linear design.
In a square design, 10km square, it would never be more than 20km on a grid to another location in the city, and usually would be much less, with the average journey well under 10km. Spread out more, to provide more natural views and access for each section, one could still make a city with much smaller travel distances. Just not with trains. Travel in a 2D city with trains involves multiple lines, and thus changing trains unless your destination happens to be on the line you’re on. Traditional cities try to design their train lines to make that happen as much as possible, and they usually have the “downtown” as the transit hub so that at least everybody can get to and from the downtown without changes. Changes mean longer and less predictable travel times, and less convenience.
But this doesn’t have to be today. Train transit involves long multi-car trains confined to rails. One reason cars are popular is that they are not confined to lines. They travel the shortest road path available, there are no transfers. Bicycles and walking also do this, at slower speeds and on more paths.
Imagined an internal 3-dimensional space within the Line.
With modern technology, it is possible to use much smaller vehicles for transportation, instead of a giant train. With robotic driving, and the important ability to turn at will and pass other vehicles along the path, breaking a train up into individual van-sized cars allows a system where people going to the same place — even on another “line” — are grouped into the same van. As such, their vehicle does not make stops, and it changes lines. In a rail system in a 2D city, the many passengers on one big train all have different destinations along the line or on connecting lines. The train stops at every stop to let them do this. If you gather all the people going from location A to location B into one van, it can then make a non-stop trip on the optimal route, the way a private car would. If there aren’t enough people taking that trip to fill a van, you can combine routes at the cost of adding an extra stop or perhaps a minor detour, but it remains far superior to the big train alternative. You get the efficiencies of combining passengers together in a group vehicle, with the convenience of direct travel that cars offer.
In fact, you may get even more efficiency, due to the paradox of size in group transportation. The more people you group into a vehicle, the more efficient you can be, but as you group more people you increase the net inconvenience to the group as they all must compromise from their ideal direct route to help the other passengers. If you do that too much, you scare away riders, lowering the load factor and decreasing efficiency. 6 vans per hour on a route will be more efficient than 1 big bus per hour because the superior service with less compromise attracts more overall riders. This is even more true if the vans make far fewer stops because they have fewer destinations among the riders.
NEOM’s city could instead offer transport with robotic vans, still making use of the reserved right-of-way under the city, providing direct stop-to-stop service anywhere in the city with smaller distances, lower travel times, and less energy, and a better experience for the citizens. It could also provide transportation out of the city with a short, sub-5 minute trip from anywhere in the city, for those who want to access the desert. It could not give so many people a view of the unspoiled desert, however. But it would spoil less desert — NEOM’s 170km line will provide a barrier to the surprisingly large number of species in the desert unless expensive tunnels to let them pass are provided.
NEOM is also considering e-VTOL transportation for the Line, such as the Volocopter. The ability of such vehicles to travel “as the crow flies” makes the linear design even worse — travel times between points would be much better in a 3 dimensional city.
Is The Line worth its higher energy cost and longer travel times just for the views? Even there, only those who can afford an outside wall will get the views, though there certainly will be a lot of desert-view offices and condos compared to a 2-D layout. A city like The Line is only possible in a place that was previously unspoiled to the extent that a 170km long stretch of land is available with nothing adjacent — that may only be in a place like the harsh desert of Saudi Arabia with a monarchy that can declare things by fiat.
A dream or reality? We believe reality.