States that Disallow Route Number Duplication

[Kacie Jane]

by the way, are there any other examples of a US route number that continues as a state route after its terminus?  like US-3 turning into MA-3. 

Formerly US 15 and NY 15.  The NY 15 concurrencies with I-390 and I-86/NY 17 are since decommissioned, and most -- but not all -- of the signs have been taken down.

[hobsini2]

Illinois does use duplicate numbers as long as the 2 routes do not cross.  When IL 5 was changed to I-88 back in the mid 80s, there was IL 88 that had an interchange with the tollway.  When I-88 was put on the tollway, IL 88 became IL 40 so there would not be any confusion. other duplicate instances that do not cross are US 6 and IL 6 (Peoria), US 14 and IL 14 (White Co), I-24 and US 24, US 34 and IL 34 (Elizabethtown), US 40 and IL 40 (Peoria), US 41 and IL 41 (Galesburg), US 50 and IL 50 (Cicero Ave - Chicago), US 54 and IL 54 (old alignment of US 54 became IL 54), I-57 and IL 57 (Quincy), US 60 and IL 60 (Town Line Rd - Vernon Hills), US 61 and IL 61 (Macomb), US 62 and IL 62 (Algonquin Rd - Algonquin), I-64 and IL 64 (North Ave - Chicago), I-70 and IL 70 (Rockford), I-72 and IL 72 (Higgins Rd - Schaumburg), I-90 and IL 90 (Peoria Co), I-94 and IL 94 (Adams Co), US 136 and IL 136 (Whiteside Co), US 150 and IL 150 (Perry Co), I-155 and IL 155 (Randolph Co), I-172 and IL 172 (Whiteside Co), I-180 and IL 180 (Galva), and I-255 and IL 255 (I-255 continues as IL 255 north of I-270).