Arizona
This is the only interstate that's signed entirely in metric. The exit numbers on I-19 correspond to its kilometer markers (for example, Exit 92 would be 92 kilometers from the highway's beginning at Sonora, and Exit 99 would be 7 kilometers away). It's a rather nice prelude to Mexico's road system, which is also signed in metric.
I-19 and I-17 could and should hook up, become one longer interstate and be renamed I-21.