

Of Connecticut's many unique interchanges, the Route 8 / Interstate 84 connection stands out: I-84 is double-decked as it crosses Route 8 and the Naugatuck River, and Route 8 is also double-decked just south of I-84.
These are the only decked sections of freeway in the state. I-91 comes close in Hartford, but its southbound lanes remain above and to the right of the northbound lanes. Double-decking has been brought up as a means of widening I-95 in Fairfield County; but to many, the only advantage of that idea is the ability to say "sure it's ugly now, but at least it's not double-decked."
The odd configuration of the interchange is a reaction to several design constraints in the area. In 1959, a Connecticut Highway Department assistant chief engineer listed them:
An interchange between an east-west highway and north-south highway had been planned since the late 1940s here. Part of the interchange opened on October 31, 1967, completing the I-84 portion; and the rest opened in summer 1968.
It was known as one of the most complicated interchanges in the country at the time, and was featured on the cover of the 1969 Connecticut state map. Below is detail from that map cover. 84 eastbound (the upper deck) goes toward the top of the page. 8 north goes toward the left.
Next is a cartographer's view; detail from the Waterbury inset, 1969 state map. What isn't visible is that I-84's lanes were reversed for a while east of there (eastbound lanes to the left of the westbound). This was fixed when I-84 was reconstructed in the 1970s.
Next is a driver's view, from Route 8 northbound, taken by Jim K. Georges. This interchange is one of his favorites as well.
Next is a postcard (not making this up), view from the southwest.
In January 2000, Wilbur Smith and Associates started a 16-month study of I-84 operations between Southbury and Waterbury. Their early assessment of the Route 8 interchange:
Deficiencies already noted include poor geometry, above average accident rate and a projected unacceptable level of service by 2025.
The final report on this study is scheduled to be complete around March 2006.