I'll start with the most extreme example in North America: US 93/95.
They duplex from between Boulder City and Henderson to Las Vegas (with I-515 joining in on the fun), and again in British Columbia for a long duplex north of Cranbrook to Radium Hot Spring as BC 93/95 -- after both have a decent duplex with BC 3!
I actually started a thread in a similar vein a while back...found it after searching:
https://www.aaroads.com/forum/index.php?topic=2152.0
You're right. This can be locked!
U.S. 80 and I-20 duplex twice in Mississippi: in the Vicksburg area and in the Meridian area.