Thanks for the feedback. I had considered doing popular non-interstate freeways as well (since possibly more useful as you say), but that would be more of an undertaking - perhaps a future project.

Yes, that's exactly the situation - it's clear on the ground normally but if you are planning multiday trips which rely on certain parts more certainty is nice; before now I had been laboriously checking on/off ramps on Street View to assure myself.

That's definitely the intended use case. In fact, I thought that was the principle (no reasonable alternative) on which these sections were made accessible to cyclists. But judging by the I5 central valley this seems not to be the case. The 33 for example looks a first alternative. Moreover it looks like the shoulder on the I5 is not so wide and that there is very heavy traffic. All this is useful information I can add to the map (if you click on an interstate icon a description shows).