Could be that in Chicago, some remnant of US-66 is replaced by I-80, but
> that would only be for a short stretch.
Nope. I drove the interstates that parallel Route 66 from Chicago to Flagstaff on my way to NARAM-48. Old Route 66 crosses I80, but doesn't parallel it anywhere. Most of the places we stayed just off the interstate were on what was old Route 66. And on the way back, we took a break and were "standin' on the corner in Winslow Arizona..."