[enneff]

Routing is much easier when you can basically go from point A to B directly. Coordination would be required to prevent collisions with other vehicles, but evasion in 3D just means changing to an uncontended altitude. I think the extra dimension actually makes it easier.

[benbristow]

I think you're right.

Planes have had autopilot systems for a while now where they basically fly themselves.

The big tech firms have been struggling to make a fully autonomous no-human-needed driving car for a while now. So many variables to deal with. Watch Tesla videos on YouTube and you'll see them still struggling on certain types/conditions of roads etc.

[thombat]

Large planes fly themselves on planned routes which avoid incursions by other planes by design: the function of air traffic control is to assign the routes such that incursions don't occur. In the event that the onboard collision avoidance system projects that another aircraft will come too close the warns the pilot with a recommended action. There is also a ground proximity warning system which issues warnings about collision with ground/mapped obstacles but again leaves it to the pilot to take the necessary action.

ATC relies upon surveillance radar that won't provide adequate coverage at low elevations (too many obstructions). ATC is also badly overstretched in busy airspaces coping with existing traffic. Adding a large number of new low-altitude aircraft will require new navigation technology (e.g. coordinating a swarm of vehicles in close proximity, relaying warnings about dangerous wind conditions or uncontrolled vehicles, etc)

Conditions in the air can be more treacherous than on a road: although there are more degrees of freedom the supporting air is also more variable than a road: wind shear and clear air turbulence can be perilous even for large aircraft, icing can quickly cripple aerodynamics, and in the event of failure safely halting can be problematic.

[bobthepanda]

Planes follow flight plans which must be pre-filed before the flight. That doesn't scale for personal travel.