I am not familiar with the soil under LA but in many cases it gets much more expensive to "stack" tunnels. The construction of the upper tunnel relies on the st

I am not familiar with the soil under LA but in many cases it gets much more expensive to "stack" tunnels. The construction of the upper tunnel relies on the stability of the soils underneath for support. Constructing a tunnel underneath may require the lower tunnel to be much stronger to support the loads. Why not just build the tunnel larger in the first place? If Musk wants to construct these tunnels, that if fine but I feel that the City of LA would be foolish to allow him to do it without ensure that the tunnels can be used for larger vehicles if the "skate" concept proves to be inadequate. This would come at little extra expense and would still allow Musk to test his concept but have a contingency plan if it does not work.