AI for 3D roads

If you mean like having something like in simcity but more complex and not a gird, you could just take all intersections and save data on what other intersections you can go to from that specific one (curves would be intersections too i guess, you could add data for how to turn and drive on intersections to make it look ok)

Then make complex AI which simulates traffic flow or something.

Hi thanks for ur reply

im stack on how to define for each city the road and connect it later with AI

i didnt find any topic on google about that, because its not like using grids ...

something like this:

Never mind grids... use nav graph nodes with edges between them. Tell the AI they can only walk from one node to the ones connected via edges. If you edges are on the roads (like in the video), the AI will look like it is staying on the roads.