Also, why would you want to bike on the shoulder of an interstate? The whole definition of a limited access highway is that only highspeed cars, going the same direction are on it, for safety.
As for biking on the shoulder of an interstate, there are areas where the only paved road going between two points is an interstate highway.
And of course there are very common borderline cases where I want to get from point A to point B, and the path on the interstate is 50 miles, while the path avoiding the interstate is 150 miles. So a trip that I ordinarily need to allot one day for becomes a 2-3 day trip unless I'm willing to pedal at top speed or for more than 8 hours. I don't want to bicycle on the interstate, but most infrastructure assumes your bike is a purely recreational vehicle.