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I-394 (proposed) Michigan
Michigan route 14, a freeway from I-94 west of Ann Arbor to the I-96/I-275 split in Livonia, is rumored to be a possible future Interstate 394. To put it more precisely (from Chris Bessert's Michigan Highways site): "...Once additional modifications have been made, one source at MDOT reportedly claims they may push for the I-394 designation..."
Even though that's four levels of indirection ("one source", "reportedly", "claims", "may"), Mr. Bessert's a trusted source for Michigan highways. (Thanks to Bobby Peacock for the referral).
See also: Michigan Highways: M-14 (Chris Bessert)
9.75 miles ; east from I-494 in Minnetonka to Washington Ave in downtown Minneapolis. Most of it is co-signed with US 12, and follows the former Wayzata Boulevard. Cost: $450 million total.
I-394 was added to the interstate system in 1968, and originally was to be called Interstate 894. In 1969, its number was changed to 394.  (It should be noted that Minnesota state documents appear never to have referred to the road as 894.) 
Construction began in 1985. The portion between I-494 and MN 100 was upgraded to freeway in pieces from 1989 to 1993.
The Federal Highway Administration (FHWA) awarded the I-394 Transit Corridor an Excellence in Design award in 1996; the award page contains an overhead photo of an interchange with HOV connections.
HOV/Toll lane scrapped
The transit corridor features a reversible "sane lane" for carpools and buses. It's sometimes open on non-commute times, such as sports events. In 1997 the idea was floated to allow solo commuters to use the lane for a charge, but public outcry caused MnDOT to drop the plan. One townsperson remarked, "You will have a lane paid for by the lower and middle class for the rich to use."  
Steve Riner (Minnesota highways)
See also: I-394 Hennepin County (Adam Froehlig)