The State of Ohio finally responded to the extortion being practiced by Linndale (the village mentioned by Dead0man) and passed a law prohibiting towns with less than 1 mile of limited access highway from ticketing speeders if they had no exit within the town. (The Linndale cops had to get on the freeway in Cleveland because they had no entrance.) The Ohio Supreme Court threw out the law because it “targeted” Linndale, which was the only town that met the criteria of the ban.
Greater Los Angeles has seen some State Routes “upgraded” to Interstates. I’m guessing that this involved considerable changes in where the maintenance money came from, but I believe that was pretty much it aside from new signs.
And new numbers, so that they could conform with the interstate numbering scheme.
State Route 7 became Interstate 710. According to this site, the switch was approved in 1984. It could plausibly be regarded as a spur of I-10.
That same year, part of State Route 11 became Interstate 110 (the part south of downtown LA). The remainder (connecting LA and Pasadena) got renamed S.R. 110, presumably to maintain number continuity. Read more here. Same story on the “spur to I-10” idea.
Evidently, opinions vary on whether this constitues another example confiscation and treachery by the feds. 