Just like software never crashes?
And if you're talking about FSD, most of those instances are from exceptions eg. unexpected pedestrian, parked truck, construction works.
Its fair to imagine that these tunnels will be custom-built for self-driving cars and will be totally controlled environments.
Toyota runaway acceleration caused by a stack overflow: https://en.wikipedia.org/wiki/2009%E2%80%932011_Toyota_vehic...
Driver error or pedal misapplication was found responsible for most of the incidents. The report ended stating, "Our conclusion is Toyota's problems were mechanical, not electrical." This included sticking accelerator pedals, and pedals caught under floor mats."