The tunnels themselves are very unassuming I'd wager that there is a lot of hidden infrastructure in a tunnel, which carries cars compared to train tunnels.

The tunnels themselves are very unassuming I'd wager that there is a lot of hidden infrastructure in a tunnel, which carries cars compared to train tunnels. 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.