Can you imagine the mess, both financially and logistically, Connecticut would make of such an endeavor?
Tunnel projects are fun. The big dig in Boston was 350% over the original starting cost numbers and it leaks like a colander. I spent my whole life in construction with the last twenty years in bigger stuff.
A tunnel like this in variable problematic sub terrain would be a change order dream for a whole team of contractors or a big bust in the middle of construction.