The problem with this idea is not with throughput of the tunnels, but with the shafts that lead to the tunnel. Lowering one car to the tunnel will take time, an

The problem with this idea is not with throughput of the tunnels, but with the shafts that lead to the tunnel. Lowering one car to the tunnel will take time, and unless there is some kind of elevator with multiple carts you will only be able to lower one car at a time. Let's say that the shaft is 20m height and let's allow 2 meters for each car. We could get ~ 10 cars "stored" in the elevator, but if it takes one minute to load and unload the car it will take ~10 minutes for the car to get to the tunnel. One shaft will be able to load only 60 cars/hour. This will not solve any traffic problems and it actually may make the traffic around the shafts worse (depending on how many cars are waiting to go into the tunnel, and how large "the Boring Station" is. There are two solutions either load/unload cars faster - possible but unlikely, or have more elevators connected to each tunnel. The problem with the second solution is that these cars have to safely join the rest of the cars that are currently in the tunnel. If you have 10 elevators, each unloading one car a minute, you would need a system that allows one car to join the traffic every 6 seconds. If the cars are traveling at 125mph the sleds would need to have a pretty good acceleration to get to that speed as quickly as possible, or you would need longer adjacent tunnels.