How about if cities were built in such a way that you would just have buildings and podium being pedestrian and bike friendly with all transportation network being 1 level underground (or 2 levels) all as self driving EV pods. This may increase the no of possible 'roads' and does not sound as far fetched in terms of overall costs. Emergency vehicles can be given an exemption to operate on the podium
Tunneling underground is extremely expensive. Individual self driving pods aka cars are very expensive. But most importantly cars do not get more efficient in capacity just because you put them underground, plus now you have to build entrances and exits to the underground system everywhere. Traveling also becomes a lot less appealing when you're in a black tube all the time rather than seeing the city around you. It's also not possible because the underground is not just unoccupied but there is already other existing infrastructure down there.
What you are describing is just a much less efficient, worse version of a subway.
> cars do not get more efficient in capacity just because you put them underground
I don't think the entire "car tunnels" thing is reasonable either, but this one is wrong. The bottleneck for cars is the inherent interference in the 2-dimensional streets. If you shove them all in a few tunnels right until they get into a low-transit region close to the destination, it would increase their capacity by a lot.
It's also a huge amount of money that is better used some other way. But it has an effect.
Surface streets aren't inherently 2D, though - you can build overpasses and underpasses and above-grade highways. We just don't, because it's hideously expensive.
pods (i guess 2 to 4 passengers) simply do not scale. It doesn't matter whether you put them underground or not. The only solution is for people to not use them.
One part of the solution is bikes, the other is mass transit. What self-driving EV pods may be able to do is be people mover for the last mile to a mass transit hub. But for individual traffic across longer distance it simply does not scale.
Underground is expensive. Cars are heavy and need a lot of ventalation. Lets leave the cars at ground level and move humans to underground or skyway systems - thus getting them out of the weather (I live where is snows so this is a very useful feature. People who live where it doesn't snow generally report hot summers and so again want to be inside anyway)
Yes, this sounds nice in principle. Also insanely expensive, difficult to build, and basically just completely unfeasible in reality.