> Because that’s hugely inefficient compared to a subway network. I live in Paris, France. 100% of its inhabitants have at least one of the 300+ subway stations under 1 km (0.6 miles) of their home.

That's actually pretty awesome, but you may have noticed that Americans don't really care about efficiency.

Once the tunnel is built, you can put anything you want into it. But I suspect we would still choose cars over trains.