That Tunnel Elon used as an example (i.e. Westwood flyaway to LAX) would be the perfect first Tunnel
As everyone knows, that 10 mile stretch of "The 5" between Santa Monica and LAX is ALWAYS bummer-to-bummer
I'd pay $10 bucks all the time to use the Tunnel.
Regarding Tunnel permits and right-of-way, I believe of you go deep enough, there's nothing in the way... no sewer lines, gas lines, pipes etc. nada
So, you'd think ultimately, once proven out, there should be little objection from anyone in govt or property owners.
Think about commercial airlines flying overhead. No one cares, right?
It just happens.