[Superman]

Red Beard is correct in both posts. Drainage is important, particularly where it's gonna freeze and thaw. Crushed rock makes the best base material. It packs more densely than gravel. It is more "structural." Concrete is the good stuff. DO NOT try to self-batch concrete for a 100-ft driveway. It would take you a month. With a good, compacted sub-base of crushed rock on top of undisturbed earth, three inches of concrete depth should work fine. Place the base, compact it, set up the forms and be sure to have a crew ready to work the concrete when the truck arrive.