Who has ridden Rt # 2 from Libby to Kalispell and how was traffic and shoulder? We'd be doing it in 2nd week June.
And from Kalispell to West Glacier? Route? Conditions? I note that Google Map Bike has some options from Kalispell to Columbia Falls that are off #2. From Columbia Falls to West Glacier seems to be primarily on #2. Shoulder w/o rumble strip?
If you are trying to get from Libby to W. Glacier, why not simply follow Adventure Cycling's Northern Tier route? MT 37 along the shore of Lake Koocanusa if fabulous. From Eureka, the NT route avoids U.S. 93 where possible. I have done Eureka to Whitefish three times. The last time was in '09. Only heavily traffic sections were in Whitefish and Eureka, although I have heard stories to the contrary. I believe Glacier Cyclery in Whitefish can give you a nice route into Columbia Falls that uses quiet, non-highway roads.
The route into Glacier debated above is N. Fork Rd. from Columbia Falls to Blankenship Rd. to Belton Stage Rd. You can stay on Belton Stage to U.S. 2 or make a right onto Lake 5 Rd. to U.S. 2. Either way, it's only a few miles on U.S. 2 to W. Glacier. Shoulder all the way.
There is an unpaved section. I think it's about 6-7 miles. I did it east to west in late June of '09 and it wasn't bad. (Also went W-E in '99 in mid-June and it wasn't bad.) 37c tires with a full load and no suspension both times. Timing may be a factor affecting the condition of the unpaved surface. A guy who led backcountry backpack trips in Glacier told me that it gets more washboardy as the summer progresses. It's very nice and quiet back there except for maybe a few outfitter trucks pulling trailer for rafts.
I also took U.S. 2 from Columbia Falls all the way to W. Glacier and lived to tell about it. When I hit it there was not much traffic. As noted, there is a shoulderless stretch before Hunrgy Horse. I would not want to do it when there is heavy traffic. I was simply feeling lazy that day.
If you have your heart set on Kalispell, I would take U.S. 93 to Whitefish and then smaller roads (E.g., Edgewood Dr.) to the Columbia Falls area over U.S. 2 to Columbia Falls. Try to stay off U.S. 2/MT 40. Rode that stretch in '09 to get from Columbia Falls to a hotel on U.S. 93 at the end of our trip. Not fun. U.S. 2 in Columbia Falls was also not fun. Lots and lots of truck traffic.