Com., Transp. Cabinet v. Babbitt, 172 S.W.3d 786 (KY, 2005)
The general rules as to liability for injury arising from a failure to maintain guard rails or barriers apply as to liability for damage to motor vehicles or injury to their occupants…. [T]he due care owed to motorists by the highway authorities may require the safeguarding of a dangerous place by the construction and maintenance of suitable barriers, guard rails or fences. While the failure to erect a barrier might not cause the accident, such a failure might be a substantial factor in aggravation of the injuries and, in that event, with proof of causation and negligence, the State will be liable.
The exercise of ordinary care is required, and guard rails need be erected only where their absence renders the highway unsafe for ordinary travel; the road presents an extraordinary condition or unusual hazard; the situation is inherently dangerous; a duty was voluntarily assumed; or the duty arises at common law or is specifically required by statute. Barriers need not be maintained where a dangerous or unusual condition does not exist.