The US 59-270 duplex in Arkansas and Oklahoma is unusual because the dominant name of the highway changes at the state line. In Arkansas, the road is locally known as Highway 270. In Oklahoma, the road is locally known as Highway 59. The state highway departments seem to agree. Here's an excerpt from the Arkansas control section map of Polk County:
As you can see, the control section number is US 270, section 1. US 59 only exists in Arkansas as an overlap. Here's an excerpt from the LeFlore County control section map:
It shows the control section number as 59. Signs along the 59/270 overlap in Oklahoma point to "Old US 59" and addresses along this section are US 59 addresses. In Arkansas, addresses along US 59/270 are US 270 addresses. Is there anywhere else in the US that a US highway changes control section designations at a state line like this?