After the Route 73 interchange, the road returns to its winding semi-rural nature, passing through Watertown and Thomaston.

After a brief suburban section through Torrington where it intersects US 202 and Route 4, it returns to a rural freeway before entering the town of Winchester.

The trunk highway from Stratford through Waterbury to the Massachusetts state line became part of the multi-state New England Route 8.

In 1951, the Ansonia–Derby–Shelton Expressway portion between Constitution Boulevard in Shelton and Pershing Drive in Derby (including the Commodore Isaac Hull Memorial Bridge) opened to traffic.

By 1957, the entire length of the Ansonia–Derby–Shelton Expressway portion was open, with the extension from Pershing Drive to Route 334 at the Ansonia/Seymour town line complete.

The last segment of freeway between Route 108 in Trumbull and Huntington Turnpike, including a new interchange with the Merritt Parkway was completed in 1982.

The Route 8 freeway was envisioned to continue beyond its present northern terminus in Winsted to either Massachusetts or southern Vermont.

In 1972, Massachusetts and Connecticut requested an interstate designation for the Route 8 corridor that included completed and yet-to-be-built sections in both states.

Newer sections between Bridgeport and Shelton, around Beacon Falls, and from the I-84 interchange in Waterbury to Winsted were designed and built from the late 1960s to the early 1980s and either meet interstate standards or require minimal spot upgrades to meet interstate standards.

Both of these segments include narrow cross-sections, tight curve radii, and closely spaced interchanges that do not meet current interstate standards.