From what I've learned/understand, the access roads on the lines are owned by the power companies. I don't think their very legal to ride, I do wheel/dirtbike on them pretty frequently. I can see how the companies wouldn't like you rutting out the roads and such. I'd worry more about the cops catching you going in or coming out. They'll probably make a big stink about it, trespassing with a motor vehicle and such. Be respectful wherever you go, off roaders have ALOT more enemies than friends.
Theres a pit in salisbury MA I go to sometimes. Maybe this spring I can show it to you.