"Tunnels" is not something that is at a "conceptual prototyping stage". We've built tunnels for hundreds of years. We know what the dangers are, we don't need a prototype to kill a bunch of people to find that out.
I'm not sure what down-voters are disagreeing with: electric cars have been in existence for over 100 years, there are very few unknowns there. Self-driving cars are a very recent development, and not a single developer has achieved widespread Level 5 autonomy. I thought that'd be pretty uncontroversial, but this is HN, I guess.