It seems cars do not consider congestion at all. I had a blue road on top first too, not used at all, shortest path (over highway) is only route considered?
Not everyone will check the traffic before driving somewhere, so it’s probably more realistic this way, but i did enjoy the extra depth of the calculations in mini metro based on the next train times vs connecting train times at the possible destinations. Something simple could still be done, based on a compromise between length and estimated time, and that would be cool to see. It does feel a little shallow at the moment, and leads to similar strategies from one game to the next