When was the Mashapaug Rd./Exit 74 eastbound on-ramp onto I-84 closed? It is on the 1971 photo but not the 1991 photo on Historicaerials.com
The ramp was probably relocated when I-86 (now I-84) was reconstructed in the area c. 1976.
The Wilbur Cross Highway (CT 15, I-86) at the time was 6 lanes from East Hartford to US 6/44, and 4 lanes to the east. That highway dated back to 1954 and earlier. Widening and reconstruction started at Union in the mid-1970s and worked its way westward, finishing around 1989 at the 84/15 split. The new profile, disregarding operational and C/D lanes, is 6+2 HOV to Vernon, and 6 lanes to the Mass. state line.
I would call this the most dramatic highway reconstruction project in CT history. I-91 north of Hartford comes close; it also had HOV lanes added, and the CT 20 interchange completely redone. But I-84 saw interchanges removed (Forbes St), moved (Buckland St. used to be at Tolland Tpke.), upgraded (flyover at 30/83); C/D roads (Manchester) and two interstates connected (291 and 384).
I doubt we'll see any project of this scale in CT ever again. There may be more expensive projects (84/8; Aetna Viaduct; 95/34/91 and Q-Bridge; Malloy's I-95 widening proposal), but nothing like a complete modernization (apparent doubling of ROW, etc.) of 30 miles of freeway.