The first step is not continuing to add to the problem. A good model subdivision/site plan ordinance will require a maintenance agreement for "use-in-common" drives. I concur with Mark. Absent the property owner cooperating, I would recommend an ordinance allowing the City to make repairs after a notice period and assigning the cost (plus overhead) to the property owners tax bills, payable over say, 10 years. Use-in-common drives were a longstanding problem in a previous jurisdiction where I worked. While it will make folks unhappy, doing the work and billing the property owners is the only way to sever the Gordian knot.