Not just that. You need telematics (you don't want cars stuck in the tunnel - if a fire breaks out, it's a death trap), you need emergency exit/access tunnels, you need ventilation tunnels, and you need all of that to run in HA mode. "Just a hole in the ground" is a very simplistic view; but perhaps this is a thought-provoking way to put it, EM is known for some radical solutions.
Ventilation, as a very critical entity, comes to mind. Also safety features are extremely critical. I live in a country with lots of tunnels and essentially every longer auto tunnel has additional tubes that are under pressure, for example. That's required if you suddenly have a burning vehicle in the middle of a narrow tube.
While car tunnels don't need to be sexy from an optical perspective there's a ton of necessary infrastructure and safety features, which aren't immediately obvious.
Maybe this changes when we all go electric, but I really don't see that happening anytime soon.