The idea of designating Route 52 as an interstate highway dates to the early 1970s. In 1982, two causes spurred the idea forward in Connecticut. The first was the desire to boost the local economy; the second was the set of recent events involving plans for I-84 to Providence.
Rhode Island cancelled its portion of in 1982, but Connecticut still favored extending the highway. It was reported that the federal government would approved the extension only if the endpoint was another interstate highway. (There are plenty of counterexamples, but let that stand.) If Route 52 became an interstate, it would be a natural stopping point for I-84, a few miles short of the state line.
In August 1982, Congressman Sam Gejdenson proposed renumbering Route 52 as an extension of I-290, which already existed in Massachusetts. Gov. William O'Neill asked the U.S. Transportation Secretary to consider the interstate designation, which was approved within a year.
If the I-290 number had stuck, Connecticut would have joined a handful of states (Nebraska, Indiana, Wisconsin, New Jersey) where a 3-digit interstate enters but its 2-digit parent interstate does not. The extended I-290 would have been more than 87 miles long.
However, in May 1983, Connecticut and Massachusetts decided I-395 was more suitable, as I-290 was well-defined as is; and the state's request for a 2-digit number, if allowed at all, would result in Interstate 99, conflicting with state highways in both states.
I-395 is continuous with I-290 in Massachusetts, and changes number at the I-90 interchange.