A parcel without legal access is largely unusable and often unfinanceable. Several doctrines can supply access, none of them reliable enough to plan around.
Easement by necessity arises where a parcel is severed from a larger tract and the severance leaves it without access. It requires unity of title before severance and necessity at the time of severance. It ends when the necessity ends.
Easement implied from prior use requires that before severance the owner used one part to benefit another, the use was apparent and continuous, and it is reasonably necessary to enjoyment.
Prescriptive easement requires open, notorious, continuous and adverse use for the statutory period. Permissive use never ripens, which is why written permission is the standard defensive measure.
Statutory remedies. Some states provide a procedure for a private road or a way of necessity, generally on payment of compensation.
Practical steps for a buyer. Confirm access in the title commitment; require an access endorsement to the policy; verify that recorded access easements actually connect to a public road; and check whether the road is public or a private road maintained by agreement.
Private road agreements should address maintenance cost allocation, standards and enforcement, because the absence of those provisions produces a predictable dispute.