Question: how dense could a city get with SkyTran?
Science fiction views of the far future envision extremely dense cities, either built like a single giant building with dozens of levels, or with people and vehicles flying in all directions around and between enormously tall buildings. Just for interest, how could a system like SkyTran some day support such extremely dense cities?
First, consider that the number of SkyTran tracks between tall buildings can scale with their height. As long as the buildings are close together and somewhat uniform in height, you can keep adding SkyTran tracks one above another, supported by the buildings as high as you like. By contrast, current skyscraper buildings with all the transport links on the ground require you to ride elevators up and down before you can go to another one. Very tall buildings must devote a good part of their volume to elevator shafts. Fundamentally, every n people added to a building require one elevator shaft, but while the number of people in the building scales with its /volume/, elevator shafts require a constant /area/. This is a fundamental limit to the height of buildings today.
Elevator cars in tall buildings are worse than mass transit, because they only usually have one car in a shaft. If they add multiple cars, they are at best limited like subways, needing to wait for one another and do "intermodal transfers" between express and local elevators and/or different heights: you have to get off at the 50th floor and change to another car that goes the rest of the way to where you want.
Instead use SkyTran for both vertical and horizontal travel -- SkyTranEqualsElevator. Just as there are two heights for north-south and east-west travel on the ground, there could be an inner layer of tracks spiraling around the building, and the layer farther away that would be the standard horizontal tracks for long-distance travel, with accel/decel tracks joining them periodically. With this design, the available transportation scales linearly with the area of the building sides. Each time you add a floor of people, you can add the same number of tracks you added for each of the other floors -- i.e. available transportation (horizontal tracks leading away from the building) scales linearly with building population, which is what you want. If a single building is very large, so that today it would include several elevator shafts and messengers on Segways etc., it would be honeycombed with tunnels for SkyTran cars moving in all directions.
Note that it is unnecessary for cars to move straight up and down like a traditional elevator. That would require accelerations over 1 G and cars that swivel from horizontal to vertical. However this is unnecessary. We think that an elevator should move up and down within one building, because that's what 1800's technology delivered.
A large building will have many SkyTran entrances, probably several on each floor to minimize long walks between offices when you arrive. Also businesses are likely to distribute operations over many buildings. Therefore only a minority of trips will be straight up and down. SkyTran cars will go directly to your destination, whereever it is. If it happens to be straight down, it simply takes a short trip around the neighborhood, moving down a succession of accel/decel tracks until it reaches the right height.
The result is a city that can grow in density (i.e. upwards) as much as desired while near-instant transport scales linearly with the volume of people. There are plenty of other reasons why city density would be limited -- desire for open space with real sky overhead is one -- but transport essentially disappears as a limitation. Dense cities, which I argue can be the most efficient technology centers AND manufacturing ones, as well as very desirable places to live, can become as dense as makes sense for all these other reasons.