Terminating sequence

[kurumi]

I-68 ends at I-79, which ends at I-77.

For a short time, while I-26 ended at I-81, you could follow this sequence: 68 - 79 - 77 - 26 - 81 - 40 - 15 - 8 - 10 - 95, where the route to the left ends at its neighbor to the right.

I'm wondering what the longest sequence might be (among any route class) without a cycle.

[Mapmikey]

I'll start with a US route sequence of 7

US 22 - 42 - 322 - 40 - 189 - 287 - 89 - 180