I-894 (numbered as another interstate)  Minnesota (link)

Interstate 894 was the original proposed number for new interstate along Wayzata Boulevard in 1968. Shortly thereafter, in 1969, the highway was renumbered to I-394. [4] Construction didn't begin until the mid-1980s, and I-394 was completed in 1993.

I-894  Wisconsin (link)

4.70 miles [2]; L-shaped west bypass of Milwaukee. The south half is now co-signed with I-43, which in 1985 was extended (renumbered) southwestward.

Between 1999 and 2002, the official mileage for I-894 was revised downward from 10.02 miles, [1] probably to reflect the overlap (even though it took effect 15 years ago).

Mayor Norquist proposes renumbering

On January 21, 2003, Milwaukee mayor John Norquist included an interesting proposal in his "State of the City" address: eliminate the I-894 designation, reroute Interstate 94 in its place, and extend I-794 westward about 5 miles to incorporate former I-94 between exits 305 and 310.

The intent: to encourage thru traffic to bypass the city center and the Marquette interchange, lessening the need for double-decking or extensive interchange work. [3] It is debatable how much effect the renumbering would have.

See also: Michael G. Koerner's I-894 page... is gone? If you find it, please send me the link.

Sources

1. Route Log and Finder List - Interstate Highways, FHWA, June 30, 1999.
2. Route Log and Finder List - Interstate Highways, FHWA, Oct. 31, 2002.
3. "Norquist gives 'State of the City' address." Journal-Sentinel (Milwaukee, Wis.), Jan. 21, 2003. Thanks to Michael G. Koerner.
4. Summers, Stephen. "Interstate Numbering aashto AASHTO & fhwa fhwa." Online posting, misc.transport.road, April 18, 2003.