Hi Shamrock,
Unfortunately, it is illegal. Please see the link below. These are all the "rules of the road" that come under Chapter 265 of the NH Statutes. The section that is most direct to your question is section 69(I)(k), but as you look through the 159 sections you will see many others that would prohibit you. Sorry for the bad news.

The backroads would probably be ok if not designated as a highway.
http://www.gencourt.state.nh.us/rsa/...OC-XXI-265.htm