How would you engineer the remedy for a long dirt country driveway that has an often impassable bedrock hill with snow/ice and mud?

Had that actually. My suggestion would be to find a company that deals with road building.....take the crest of the hill down with a Jack hammer will make the hill easier to climb. Bedrock is very slick when snow and ice is present, cut washboard grooves in it to help with traction. A four wheel drive truck helps, and if nothing else park at the bottom and walk, or get a four wheeler to go back and forth.