Legally speaking, if two properties share a driveway, it is the responsibility of each owner to ensure that the other owner has access to and can use the driveway. If one person is trying to block or limit the other's access to the driveway, sometimes legal proceedings are required to enforce fair use of the driveway. Typically people can find ways to coexist and come up with informal agreements that govern how the driveway will be used.
No driveway stays in perfect condition forever, and if a driveway starts to crack or has water drainage problems, then it needs to be fixed. In a shared driveway, it can be unclear at times who is responsible for arranging and paying for maintenance of this type. It is a good idea to have the responsibilities for repairs specified in the legal documents that outline the joint ownership of the driveway.
Usually, a driveway is not actually owned by several parties, but one or more parties have an easement that legally entitles them to use the driveway belonging to someone else. When a property is sold, if a driveway easement exists, it is sold along with the property. Problems arise when an owner of a property wants people to stop using his driveway, because if they have legal easements, he cannot legally block their access to the shared driveway.
Another consideration with a shared driveway is the regular care that must be performed on it. For instance, in climates that receive snow, shoveling duties need to be assigned, while in other areas driveways might need sweeping or leaves removed. The shared responsibility over these types of duties should be formalized in writing to avoid conflicts when one party shirks responsibility on the chores.