[Axien]

Why would 20 cars be constantly on the road? The cars would sit in parking lots, ready for a call. The actual road traffic, will not change. 1000 people going to work is 1000 people going to work irrespective whether they own the car.

The biggest change would be the lack of a need for parking. This will allow us to build more densely.

[frumper]

You'd have more cars constantly on the road because the smaller pool of cars has to also travel to where the people are. If I go from A to B and later from B to A, a robotaxi would also need to get to A and B when I need them. It really won't matter if they're in use or drove off to a parking lot somewhere else, that is extra traffic.

[Tiktaalik]

The amount of traffic will increase because people who couldn’t drive before and would ride with other people or use public transit (eg. children and the elderly) can now hail cheap autonomous cars, inefficiently using an entire car for their trip.

Induced demand economics. Make something cheaper and people use more of it.

If Autonomous cars make ride hailing cheaper we’ll see an explosion in its use, and traffic will increase as cars are space inefficient and road size fixed.

[bluGill]

Wait, are there 1000 people going to work, and then the car parking outside of work? Or are those cars leaving where the people work to go elsewhere? the later creates more cars on the road. Sure those 1000 cars can go somewhere to park - but now we can't build much denser as we still need parking for the cars. Maybe we can move the cars out a bit for more density where people work, but then we need roads to get those cars back out.