I-184  Idaho (link)

3.62 miles [1]; Idaho's only 3-digit interstate; serves Boise.

On Dec. 12, 1968, the Boise West Connector was dedicated; this is now part of today's I-184 leading from I-84. [9] At the time, I-84 was known as I-80N, and the Connector was I-180N, the only 3-digit interstate that has ever had a letter suffix. (Pennsylvania's I-80S -- now I-76 -- had three 3-digit interstates, but they were known as Interstates 280, 480, and 680, without the suffix.)

The route has also been signed Business Route 84; I don't know which years each designation was in effect. Nick Webster reports that the official 1974 ITD map shows the Connector simply as ID 55. [11]

On July 1, 1980, at the direction of AASHTO, the letter suffixed I-80N was changed to I-84. [6] [10] This was part of a larger effort to phase out so-called letter-suffixed interstate numbers; I-15W, also in Idaho, became the western Interstate 86. I-180N followed the I-84 change and became I-184.

In 1990, I-184 was extended to downtown Boise. [9]

These days, I-184, the old Boise West Connector, is simply called the Connector. [5] [9]

See also:

• Interstate Guide: I-184 (AARoads)
• I-184 (Zach Maillard; broken .edu link; waiting for new one!)
• misc.transport.road FAQ: Letter-Suffixed Interstates (A list of all such routes; all but I-35E/W are gone now)

I-184 (cancelled)  Rhode Island (link)

If Interstate 84 had been completed to Providence, as was planned in the 1970s, RI 10 between present-day US 6 and I-95 would have been called Interstate 184, according to at least one planning map. [8]

I-284 (cancelled)  Connecticut (link)

I-284 would have run about 5 miles from the I-84/CT 2 interchange north to I-291 in East Hartford.

I-284 died in the mid-80s because of environmental concerns. The Governor Street "Evel Knievel" ramps (I-84 exit 56) were the planned start of the highway.

More details: see I-284 at Connecticut Roads.

I-384  Connecticut (link)

8.20 miles [1]; east from I-84 in East Hartford to US 6 and 44 in Bolton Notch. Interstate 384 was once part of Interstate 84, but became I-384 in 1984 when I-84 was rerouted. It now serves as a Manchester bypass.

More details: see I-384 at Connecticut Roads.

I-484 (cancelled)  Connecticut (link)

Never completed, I-484 would have run from I-91 exit 29A west through Hartford, underneath Bushnell park, to connect with I-84 exit 48 near the Capitol.

More details: see I-484 at Connecticut Roads.

I-684  New York; Connecticut (link)

28.47 miles [1]; from I-84 in Brewster to I-287 in White Plains. Interstate 684 was originally intended to be part of I-87. Its most notable feature is a 1.41-mile cut through a corner of Greenwich, Connecticut, with no interchange in that stretch. No other interstate highway passes through a state while providing no access in that state.

More details: see I-684 at Connecticut Roads.

Sources

1. Route Log and Finder List - Interstate Highways, FHWA, Oct. 31, 2002.
5. Portland763. "I-184 is 'the connector'." Personal email, Aug. 15, 2000.
6. Idaho Transportation Board. Supplement to the March 1979 meeting of the Idaho Transportation Board. April 10, 1979.
8. De Cesari, Shawn. "Interstate 184 and other various bits." Personal email, Oct. 24, 2001.
9. Idaho Transportation Department, "WYE Interchange Reconstuction Project." http://www2.state.id.us/wye/stage2.htm (9 Sept 2002)
10. Oregon Department of Transportation. "A chronological history of ODOT: 1899 to 1993." http://www.odot.state.or.us/ssbpublic/bss/rmds/history/~chron.htm (12 March 2004)
11. Webster, Nick. "I-184/180N." Email to Kurumi, Sept. 6, 2005.