Interstates with No Auxiliary Routes by FlaxmanR

Question 3

Joining I-90 on the southeast side of Rockford, Illinois, it does not have its own unique roadbed again until splitting off from 90/94 south of Portage, Wisconsin, after a 29-mile stretch (following I-94’s joining at Madison) that is the longest concurrency of three interstates in the country. Which interstate otherwise runs from Normal, Illinois to a point just shy of Wausau, Wisconsin?