I'm still in the middle of a road trip, but so far managed to clinch (counting previous travels) US 85 and US 412, plus as reported here I-49 with its latest extension north of Shreveport LA. More US route clinches likely on my long trip back home from California.
The US 85 clinch proved costly. For me, to clinch a border-crossing highway, you need to drive the route across the border (others are less fussy than me), so that meant a short foray into Ciudad Juarez, Mexico. On the way back, my pickup truck overheated in heavy stop-and-go traffic on a one-way bridge over the Rio Grande, which drove the outside temperature to at least 130F since I was surrounded by other cars with hot engines. After shutting down my engine, I wasn't able to restart it. I was able to coast most of the way downhill from the crest of the bridge to U.S. customs (without help from power brakes or power steering), but Customs personnel had to push my truck the rest of the way to the booth, and then once I was cleared, push it out of the customs area to a place a tow truck could reach. No permanent damage, but it cost me several hundred dollars and threw me off schedule by a day.
I hope Jim's car troubles on his latest trip were less interesting and expensive.