Comment by Ekaros

On concept level they kinda make sense. But the trade-offs are just too stupid. Basically it is equivalent of building tunnel around all of the roads. The energy investment in that sort of infrastructure is unfeasible. And then partial vacuum, that needs more infra and energy to be spend.

And then the safety, on ground level open air is great, you can exit at any point to any direction. But tunnels especially small ones... That would be nightmare in best case and death trap in the worst.