Longest unclinched roads you've driven both ends of

[clong]

Interstate - I-44 - 647 miles - have driven Wichita Falls to OKC and I-270 to the Eastern end in St Louis (and also a small segment near Springfield, MO)

[therocket]

US-89 (1,252 miles)

I've only done the segment from Flagstaff to Page, the Bryce Canyon-area segment, and the US-2 to Canada segment.

[pderocco]

When I did my Arizona clinch trip last month, I drove the westernmost few miles of US-64, way up near Four Corners. I had driven the eastern end out to Cape Hatteras back in 1991. I didn't realize they were the same road until entering the data into TravelMapping.

[paulthemapguy]

Either I-64, US31, US45, or US51. Probably one of those.