Here's a link on laws for using the Interstate:

http://www.fhwa.dot.gov/interstate/faq.htm#question15

In Kansas, bicycles are prohibited from using the Interstate. However, there are still some four-lane divided highways, U.S. highways and State highways, where bicyclists can ride. There is also a major interchange in my hometown that involves an Interstate, a Kansas highway, and a major city street which we've biked through (on the city street - which gets the least and the slowest traffic). Going through (and not using the off ramps) is scary, especially when the car traffic behind us doesn't signal, but the drivers don't usually seem to know what to expect from the bikes, either. We usually either stop on the shoulder (giving the stop signal) well back from the off ramp, or if there is a break in traffic we look over our shoulders, give a left signal, and move into the right through lane. If we're lucky, there is little or no traffic behind us and fortunately, that is often the case there. Besides the area with that interchange, I avoid that kind of riding.