I dont know about power lines but the Rails-to-Trails org provies maps that cover converted railroad lines. These trails are great on a mountain bike or ATV. You might get a good SUV or even a car down some in a true emergency (you do not want to practice this before hand).

Many of these trail go surprisingly deep into many large cities.

http://www.railtrails.org/

http://www.traillink.com/