I know we all know that Connecticut and its Turnpike has the most exits per mile than any other road in the nation. The only other contender would be I-295 in Gloucester County, NJ where concurrent with US 130, but that section is only 14 miles in length compared to the 128 miles of the Connecticut freeway.
Other than these two routes how many other freeways have interchanges in close proximity of each other?
I will say I-278 in New York would be one as it has more exits than actual miles. If New York ever converts to mile based exit numbers, I-278 would have a lot of suffixed letters exit numbers and you would find exit numbers like Exit 40 in Queens to disappear and all the numbers in the Bronx reduced. Any other contenders of several miles? No short city connectors must be a freeway of considerable length.
This might be a bit difficult, since in cities where there are a lot of interchanges, a lot of them are half-interchanges.
Anyway, the Kennedy expressway in Chicago (officially starting in O'Hare and ending at the Circle Interchange via I-190, I-90, and I-94) is 17.8 miles long with between 35 and 40 interchanges. When the exits get this dense, it's hard to determine whether a ramp or two is part of an interchange, especially if they're one or two blocks away from each other.
To put numerical values to the OP, the Connecticut Turnpike is 128.47 miles with 93 interchanges, making it 1.381 miles/interchange.
The segment of I-295 is 12 interchanges in 14 miles, so that's 1.167 miles/interchange
I-278 has 57 interchanges (including both ends) in 35.62 miles, so it has 0.625 miles/interchange.
Similarly, the Kennedy has an interchange every ~half-mile.
The Lowell Connector has 5 interchanges in 3 miles.
Rochester's Inner Loop has 0.325 miles/interchange with 8 interchanges in 2.6 miles.
The US 30 bypass loop around Lancaster is about 0.7 miles/interchange, even after reconstruction in the 90s to consolidate at least two of them.
I-295 in Gloucester County (noted above) is what immediately came to mind when I read the topic. No local road was denied an interchange in that stretch, and a couple retain their original tight ramp geometry.
The I-95 portion of MA 128 (Canton to Peabody) is roughly 1.12 miles/interchange*.
*If one treats/views Exits 32A-B (US 3 North & Middlesex Tpk.) as separate interchanges (they were numbered as 43 & 42 respectively pre-1988); the figure comes out to 1.08 miles/interchange.
Pre-Big-Dig, I-93 along the Pulaski Skyway/South Station Tunnel/Central Artery (Mass Ave. to US 1 North) is about 0.33 miles/interchange. The figure was originally lower prior to some entrance/exit ramps being removed during the mid-to-late 70s.