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I-305 (cancelled) Oregon
This is the proposed but unbuilt Salem Spur, intended to connect I-5 to city streets in North Salem. I-305 would have followed the Salem Parkway (now Business Route 99E). Its official length in the federal highway log was 3.3 miles. 
In 1977, I-305 was withdrawn from the Interstate highway system. Funds were traded in for road projects in the area, including widening of the major bridge across the Willamette River to West Salem. 
I-305 still appeared in some later road atlases, including the 1985 nationwide edition by Rand McNally.
See also: Interstate 305 (Cancelled) (Mike Wiley)
I-305 (not signed as interstate) California
8.44 miles . Interstate 305 is merely a funding designation for a portion of Sacramento's Business I-80, from the real I-80 to the US 50/CA 99 interchange. Not only are there no "I-305" signs posted, the route doesn't even have a legislative (state) numbering of 305.