Route 1 and US 101 in California - prior to 1964, Route 1 had both south and north termini at US 101 (once the former Alt US 101 was added then, this was no longer the case).
I-5 and Route 99, the southern terminus is definitively at I-5 and the northern one comes very close, while there is a concurrency in Sacramento between downtown and the suburban Natomas area.
Implied but not signed is Route 193's concurrency along Route 49 in Auburn (after Route 49 junctions with I-80), 193 makes an L shaped loop before ending at Route 49 north of Placerville.
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Outside of California, the obvious example is I-90 and I-94 (two concurrencies, with I-94 having its west terminus at I-90 in Billings).