Interstate 84 in Connecticut

I-84 opened in stages from the New York State Line in Danbury starting in 1961, finally connecting to Hartford in 1969. In Hartford, it crossed the Bulkeley Bridge and continued along the existing Wilbur Cross Highway to Massachusetts. This western segment was briefly redesignated I-86.[2]

A highway connecting Hartford and Providence was first brought up in 1944 as an upgrade to US 6 from Manchester to the Rhode Island state line.[3][4] The plan eventually adapted to a submission to the 1956 Interstate Highway Plan but was declined. It was resubmitted in the 1968 plan and was granted along with 1,500 other miles (2,400 km) of Interstate.[5]

The highway was firstly designated as Interstate 82 (I-82) but was changed shortly after to its well-known designation, Interstate 84 (I-84).[5] In 1970 through 1973, the first segments of the highway started construction, the segment now designated as I-384, and the Willimantic Bypass.[3] When these isolated segments were completed, they were designated for the future Interstate, starkly different from today's signs. The signs remained on the Willimantic Bypass up to a decade after the cancellation of the project.[6]

The planned I-84 was going to also incorporate a cloverleaf intersection with I-295 in Johnston, Rhode Island, and use the under-construction Dennis J. Roberts Expressway and built Huntington Expressway to Providence before the project was shelved.[7] Briefly, there was an idea to use the southern/unused portion of the highway for Interstate 184 (I-184) but was disapproved by the FHA.[8]

An environmental study by the Rhode Island Department of Transportation (RIDOT) was done in 1972; it was found the highway would cause heavy impact to Scituate Reservoir, the main drinking supply for Providence.[9][10] After conducting multiple other studies, including briefly considering an alternate southern alignment that would bypass the Scituate Reservoir to the south and connected I-84 to the Route 37 Expressway, Rhode Island ended up canceling their segment of the highway in 1982, which ended up causing Connecticut to cut the segment to I-395 in Plainfield.[11] Without Rhode Island, the highway was fully canceled in 1983, and the mileage was returned for other projects.[12][13]

After the highway was canceled, the only inland route to Providence from Hartford was either US 44 or US 6. Many projects have since happened to improve the roads, mainly in Connecticut.[14][15] One major one was improving the "Suicide 6" area of US 6 between Bolton and Columbia.[16][17] Since the cancelation, other plans to have a freeway link between the two built segments have been proposed, including one in 2001, but was short lived, only lasting to 2003 before becoming dormant.[3][18]

In the 1992 long-range transportation plan released by RIDOT, a freeway has been added along the original route of I-84 that will connect to the Route 695 freeway on the Rhode Island–Connecticut border.[19]

The section of I-84 between East Hartford, Connecticut, (at the present-day junction with I-384) and Sturbridge, Massachusetts, (I-90) was for a time signed as I-86 (unrelated to present-day I-86 in New York and Pennsylvania). Signs stating "I-84 Ends, I-86 to Boston" (eastbound) and "I-86 Ends, I-84 to Hartford" (westbound) were posted where the change took place. Exit numbering on I-86 was that of the road's predecessor, Route 15, in a sequence beginning on New York's Hutchinson River Parkway. Exits were renumbered to correspond with the rest of I-84 in Connecticut when the road was redesignated in 1984. The present I-384 as well as the present US 6 bypass near Willimantic, both of which were a part of what was then I-84's planned easterly continuation, were also numbered I-84 prior to 1984 even though they lacked any direct connection to the rest of I-84 at that time. (One had to use Silver Lane in East Hartford to travel between the two stretches of the highway.) These two sections were renumbered. The western segment became I-384, and the eastern one became part of US 6 when what was then I-86 was renumbered I-84.

Danbury Rest Area and Information Center on I-84 eastbound

Sections of I-84 in Connecticut were reconstructed and widened from the mid 1970s into the mid 1980s. Another section through Danbury was widened from four lanes to six lanes in 1985 and 1986. Widening of the highway through Danbury was funded by Union Carbide as part of building its world headquarters in Danbury.[21] From roughly 1976 to 1988 the former I-86 portion from East Hartford to the Massachusetts state line was completely rebuilt from a narrow four-lane parkway to a much wider profile ranging from six lanes at the Massachusetts state line, expanding to eight lanes in Vernon, to 12 lanes with high-occupancy vehicle lanes (HOV lanes) in East Hartford. The original route, then known as Route 15, featured pit latrines at its pull-offs or rest areas. As of 2014, planning is underway for the I-84 Hartford Project to replace and possibly redesign a two-mile (3.2 km) stretch of mostly elevated highway in Hartford. On April 22, 2015, construction began on widening the highway from exit 23 to exit 25A in Waterbury from four lanes to six lanes.

A widening project along the congested stretch of I-84 through Waterbury and Cheshire has been beset by cost overruns, delays, and construction defects involving storm drains,[22] as state and federal officials have launched criminal investigations stemming from this project. This episode has waned local enthusiasm for a proposed $2-billion reconstruction of the Mixmaster interchange in downtown Waterbury.[23] Cost estimates for the Mixmaster replacement have increased to $3 billion.[24] Connecticut Attorney-General Richard Blumenthal has begun a lawsuit against the contractor and an engineering firm in response to threats from the US Department of Transportation (USDOT) to withhold funds from the project.[25] On May 18, 2007, the Republican-American reported this area had defective light poles,[26] while Governor Jodi Rell released an audit report of the construction disaster.[27]