Had to ride a couple of stretches of I-90 west of Missoula during my recent trip. The first one was about 4 miles. No other alternative. Yes. Not inherently bad, but not the most pleasant riding. Very noisy at times. And that was early on a Sunday morning. I would definitely not ride one for 117 miles if there were reasonable alternatives. It looks like there are sections of through frontage roads between Great Falls and Boulder.

As luck would have it, the westbound lanes of the other two sections of I-90 I was forced to ride were closed to cars in preparation for roadwork. (Westbound vehicle traffic was being routed in the fast lane of the eastbound side.) Having an entire Interstate Highway to one's self is fun. I just went through the barricades, took to the roadway and hoped no bridges had been torn out.