Iin the future the most likely scenario is that all vehicles will be driven by tesla's FSD because nobody else's software or hardware stack is currently in a viable position to compete against it, and thus will not be approved by regulators before tesla is able to monopolize the entire market... unless those regulators are bad-faith actors trying to push dangerous inferior systems in the name of nepotism
an emergency-access route is just a straight tunnel-bore down, presumably with a stair-case and an elevator
there's no way that could ever constitute a non-negligible cost
ventilation systems are unnecessary for the majority of the tunnel distance because EVs do not produce exhaust fumes
i'm not entirely sure how accident logistics would work, but i assume that based on current FSD and autopilot statistics the probability of accidents occurring in a path that's single-lane and straight-line and also driven by software and not a human being is extremely low
given relatively straight tunnel geometry, damage to the tunnel's reinforced walls would be negligible regardless of the speed which the vehicles travel, and majority of damage would be to vehicle bodies
which means ideally you'd probably just send a cybertruck down with a giant bulldozer claw welded to its face and use that to push the wreckage to the nearest car-sized elevator
and you'd send an emergency vehicle down to pick up stranded passengers
traffic can be redirected away from the tunnel in which the accident occurred and moved via elevator to different tunnels sections or surface roads.
