One idea I’ve had pretty much since the beginning is to secure the city via walls. However, goods still need to flow in and out of the city. Borrowing from Elon Musk’s tunnels/elevators idea here’s how most goods will be brought into the city.
Outside the walls will be a truck stop type area where semis and their trailers can check in with authorities. The load will get scanned and checked, if appropriate. The shipping container will be craned off of the truck and onto a platform sled. This sled sits on an elevator of sorts. Once the computer is the load has been scanned, the elevator will quickly go underground and find its destination via a dedicated tunnel. Recipients will be notified of its arrival. They have a set number of hours to unload the trailer. When it is unloaded, they scan the container and notify the system that it is ready for departure. If there are any pickups, then the container will stop at those destinations until notified that loading has been completed and finally make a return trip above ground. The truck driver is notified that his trailer is ready for departure so he rehitches it.
Off he goes. This system controls access to the city and eliminates questionable drivers from the city reducing traffic deaths.
We might also bury parking garages underground and use similar sleds to park personal cars so people won’t be driving those through our tunnels. They would drive to the city into the truck stop, find the elevator for personal cars and walk to enter the city.
I like this. It sounds futuristic to me.