I would hate to ride westbound on US 26 from Ontario to Austin Jct. - but eastbound is super.
Some killer downhills and, usually, a tailwind. It'll take 20 years off your face.
In 2015 I didn't get the prevailing tailwind, but the time before I was coasting in my big ring.
It really is one of the finest rides in eastern Oregon. And there is almost zero traffic until Vale.
There's a lodge at Austin Jct., store & cafe at Unity, nothing at Ironside, store long closed at Brogan but park with water, store at Willowcreek.
There's also a lovely back road along the bluffs from Vale to Ontario - much nicer than busy US 26.
(The TransAm section is fine - longer by 50+ miles - but Hwy 55 riding should be the minimum.)
About ID 55 - it has few shoulders and pretty heavy traffic.
As with all roads, it has different traffic levels depending on month, day, hour.
Much of the traffic is recreational - and not much commuter.http://apps.itd.idaho.gov/apps/roadwaydata/counters/184/index.htmlhttp://apps.itd.idaho.gov/apps/roadwaydata//184SouthBanks/2016/16-06jun/T184_SouthBanks_Jun16_MonthlyAverageHourlyTrafficReport.pdf
June - 8000; July 10,000 - - Neither is good.
Weekends have almost twice as much traffic as early weekdays.
Friday afternoon/eve and Sunday afternoons are the worst.
7:00a traffic is low every day (200 per hr) 7:00p traffic is low M, T, W (300 per hr)
This is why you get some people on websites saying - "That road was no problem."
While others say, "It was a death trap."
About Sage Creek Rd - How skinny will your tires be? Touring width? 32s or larger? I didn't have any problem with 1 3/8s. (35)
Of course, if there's a big storm, that's different. But the road is probably best 12 hours after a rain. Solid, not too much dust.
The scenery is muted - maybe one or two cars an hour - so you are not in trouble if something goes wrong.
And it allows you to ride the entire main road thru the park. Evening and early morning are best light.