A video yesterday reminded me of the Saudi Line proposal to build a brand new very linear city (or linear arcology, one long building) in western Arabia. I looked again at the numbers, and wow it is nuts.

170 km long.

500 m high.

200 m wide.

(Area 34 km2.)

It's supposed to be higher than it's long! Crazy. You could probably bring the cost down just by flipping those two numbers (though maybe ventilating a 500 m wide building would be a bit more challenging, I dunno.)

For minimizing trip lengths you would want a circular city, or something close like a diamond or grid. But I can see some appeal of a linear city: simplifying your high speed transport by needing just one backbone route, and keeping it easy to go outside the city into a greenbelt/preserve. (Not sure how much point to that there is in western Arabia, but anyway.) So I wondered what a saner proposal might look like.

1) drop the arcology and just go with a conventional city with streets and buildings.

2) Have the width be at least a 5 minute walk from edge to spine, so 400 meters, making it 800 meters (10 minutes) edge to edge, which avoids the need to have any cross transit. This is 4x the width, so could reduce the length from 170 km to 42 km. (Though the original proposal used the height to be very high density, which I'm kind of waving away.)

You could double the width, for a 20 minute edge-edge walk; 1.6 km x 21 km.

But since you're trying to avoid cars, you should go in for bicycles and other micromobility, at let's say 3x expected walking speed. 2.4 km edge to spine, and 4.8 x 7 km in shape... which is actually almost a square, whoops. And you'd probably need cross-transit again for the minority who can't use any form of wheels, or the larger group who don't always want to. Still, it's a city where every point is a 10 minute bike/fast powerchair ride to the central spine, at 15 km/hr.

San Francisco is actually bigger than this, so I've just discovered that SF could be way nicer than it is (granted SF has hills.)

To keep a line shape better, go back to the 10 minute width of 800 meters, triple it for bikes, now you have a 2.4 x 14 km city, and can get some real rail use out of your backbone, while it's still a 15 minute walk from the center to the edge.