I will be coming out of SD on US 212 into MT, over to Crow Agency (Little Bighorn Battlefield). I would like to then get on US 12 W to 89 N thru Great Falls up Glacier Park. (1) It appears that 212 ends in Crow Agency and joins I-90 for 10-15 miles to Hardin; then I could take 384 out of Hardin to Billings, then 3 N to Lavina where I could pick up 12. (2) Or, I could take 47 from Hardin N and pick up 12 in Vananda; (3) or backtrack from Crow Agency to Lame Deer then N on 39 toward Forsyth to pick up 12 there. I would prefer the Billings route, but can I ride on I-90 for a few miles? That is a big no-no here in Alabama. Other suggestions? Thanks.
About interstates -
Bicycles on interstates are legal in most Western states outside of metro areas.
Each state has limitations published online on its DOT website.
Usually there is a wide shoulder - riding is generally safe.
But the shoulder often has rumble strips, road debris, and traffic is usually heavy.
US 212 is not a particularly good choice in SE Montana - western half worse.
Although it has shoulders for most of the way, traffic is heavy - truck traffic.
Truckers use US 212 to cut off extra miles from I-90.
There are service roads and Old Highway 87 from Crow Agency to Billings.
But the Billings area is not especially easy to bike thru.
If you are headed towards Glacier NP, then
US 212, MT 39, Old US 10 East, US 12, US 89 is the best route.
US 212 has lighter traffic east of Lame Deer, but some steep climbs.
MT 39 has moderate traffic but has been recently repaved north of Colstrip.
US 12 is a nice cross-state route (have done it).
Fairly light traffic except between Lavina and Harlowton.
The section west of Forsyth is pretty remote - bar/cafe at Ingomar.
US 89 over the Belt Mtns is a lovely, quiet ride.
MT 47 north to Vanada - Huh??
Narrow, dangerous - no paved connector to US 12.
jamawani, thanks for the info, very useful, as have been your responses to other questions I have posted. I have driven 212 to Crow Agency, but it was 20+ years ago, and my memory of the road conditions is non-existent. I want to go thru Ashland as there is a school for Native American kids that I have supported for many years, and a small college in Lame Deer as well. I guess I will risk the truck/rv traffic, I've ridden US 82 and 84 across Alabama and Georgia, heavy truck traffic with no shoulder; didn't like it, but did it. I've been hit before, sideswiped by a SUV @ 75 mph; that's not much fun, but I try to be very attentive since. I like the looks of 39 on the map and 12 over to 89, thanks for the suggestion. I've driven 89 up to Glacier Park, so I look forward to that. I will not climb Going To The Sun Road, but will turn southwest toward Idaho from there, I want to follow the Lochsa River and go over Lolo Pass. I suppose you've been that route too Suggestions are welcome.