I-10 took over part of US 90 and I-90 took over much of US 10.
I-70 bypassed/replaced most of US 40 east of Denver and I-40 bypasses/replaced US 70 east of Little Rock
Since the Interstate and US grid are flip-flopped, you would expect this to be the case more often than not.
I-80 bypassed US 20 through Indiana and part of Ohio
I-20 replaced/bypassed US 80 from Texas to Mississippi
US 91 is erased by I-15 until a short stretch in ID.
Quote from: STLmapboy on May 14, 2020, 10:00:27 PM
US 91 is erased by I-15 until a short stretch in ID.
But I-91 didn't replace US 15.
US 22 → I-78
US 78 → I-22
(at least parts of both pairs)
US 66 (part) -> I-44
Quote from: ozarkman417 on May 14, 2020, 10:41:40 PM
US 66 (part) -> I-44
But US 44 never became part of I-66. That's the other half of the game.
Quote from: STLmapboy on May 14, 2020, 10:00:27 PM
US 91 is erased by I-15 until a short stretch in ID.
And I-91 replaced CT 15 as the primary New Haven to Hartford route in CT (15 still exists, but you wouldn't use it for the entire trip).
Bit of a stretch, but here goes:
I-55 follows part of (former) US 66.
I-66 follows much of VA 55.
I-35 follows US 69 from Kansas City to Des Moines. US 35 is concurrent with I-69 between Marion and Muncie, Indiana.
In a somewhat different vein: Manitoba 18 is a continuation of North Dakota 30, and MB 30 is a continuation of ND 18.
This is a bit of a stretch, but: I-40 and US 64, and I-64 and US 40. Only reason I call it a stretch is that US 40 only follows I 64 for 45 miles or so around the St Louis area. If I-64 replaced anything, it would be US 60 and 460.
I-40 follows US 64 from Warner, OK to Conway, AR; which isn't all that long, either.