[aeternum]

1) The "attach" would likely be virtual, just meaning a tight following distance. You could have optional shock absorbers if you're really worried about collisions in the tunnels. Most likely not needed though.

2) Yes I'm surprised also. Any theories on why? Too much of an edge case for tesla's focus?

3) I think yes but very few building have heliports, far more have parking garages that could double as tunnel ingress/egress. I think both will be used but tunnels support higher density and have less dependence on weather.

[jraph]

> if you're really worried about collisions in the tunnels

Cars can fail, you have to leave enough room to allow cars behind to stop in time to avoid a (cascade) crash.

[aeternum]

This is mostly due to human attention and how the human vision system works.

[jraph]

There's also inertia, especially for cars that heavy. You can't go from 140 km/h to 0 instantaneously.

(yeah, taking 140 km/h, quite high for a car especially in tunnels like this, but anything slower would be slower than our slow trains and would be quite disappointing)