that's an interesting question. I know under the law if under the influence of a substance it is illegal. The same can be said that you can make errors of judgment when tired which can lead to...
http://www.youtube.com/watch?v=498eP_ttP-A&feature=related this exact thing happened to a friend of mine... don't drive distracted. if you're moved by this, please press "like" on youtube to end...