Interesting that pretty much all of the other proposed freeways/expressways as of 1970 were cancelled with the exception of the double decker I-93 bridge connecting to the pre-existing Central artery in 1973.
I've mentioned this before in other threads, but it bears repeating here. Construction of what are now the I-93 upper and lower decks was begun in late 1969, and was completed by mid-1971. This roadway was intended to be part of the I-695 Inner Belt, but the section that was built was principally intended to serve as a direct connection between I-93 and the Central Artery. The reason this road wasn't opened at the time it was completed was not so much because of Governor's Sargent's 1970 moratorium on highway construction, but had more to do with concerns about traffic issues due to both the short weave section over the Charles River and a proposed direct connection ramp from Rutherford Avenue to the upper deck, and a similar ramp from the lower deck to Rutherford Avenue. These two ramps were never built.
The event that finally prompted MassDPW to open the upper and lower decks to traffic was the sudden closure of the Tobin Bridge due to a gravel hauler that hit one of the support bents - see
https://www.aaroads.com/forum/index.php?topic=10395.msg246301#msg246301 for more details. However, the upper and lower decks (which never sported I-695 signs or shields) did not officially get the I-93 designation until late 1974, and weren't signed as such until mid-1975.
An early episode of the show
Banacek titled
Project Phoenix, which was filmed in early 1972, has some nice aerial shots of the I-695/future I-93 upper and lower decks, completed (minus the aforementioned Rutherford Avenue access ramps) and ready to accept traffic.