I cut down several oak trees and a few pine trees. I was able to break up and remove the roots after about 4 years. Ity was still hard work. The alternative (if you are going to put on a driveway) is to grind the roots down to the level desired for the driveway base. If a normal base is 4 inches deep, make your 6 inches. When you are preparing for the concrete poor, add an addition two inches of crushed rock, then tamp it down flat/level and ensure that you have a good amount of steel wire mesh in the contrete to prevent breaking apart. You may want to double the amount normally used.