Pretty amazing coincidence...
Heading west from Portland, US 26 enters the path of totality near Mt. Hood, and remains within the path for about 330 miles, all the way to the Idaho border:
(Updated 1/30/2020.) It is common for two different US routes to overlap (meaning they are concurrent along the same highway for a certain distance before splitting apart again).
It is less common for three (or even more) US routes to overlap. For example, traffic heading west from Cody, Wyoming, towards Yellowstone is on US 14, US 16, and US 20 (all at the same time).