This is a subject I have thought about before but never put much more into it besides an initial thought. But some other people/places have gone much farther with the topic. The folks over at Biking Bis had a nice post about the History of Railbiking.
This picture is from the Railbike Tours, Inc. website, where you can purchase a railbike or tour etc. Seems like a great idea doing the railbiking as another method of avoiding too much contact with automobile traffic when biking. But the mere hassle of trying to get permission from the rail owners makes this seem a bit prohibitive.