Here are some pictures I shot this morning:
I'm standing near the pactice range at Colony Cottage (across the street from 466A) looking west.
Here's a close up with the Morse Blvd starting to cover the tunnel. We are looking west and Morse Blvd. is running over the tunnel from right to left:
Finally, here's a closeup of the tunnel. It is roughly 20 feet wide but each section is only ~ 8 feet deep so it could have been brought in on flat bed trailers without needing wide load permits.